Members/tobaru/cbc/CbC_llvm: docs/ExceptionHandling.rst annotate

annotate docs/ExceptionHandling.rst @ 16:d405342cecb1

can eliminate tail call regardless of optimize level

author	Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp>
date	Tue, 24 Sep 2013 19:04:26 +0900
parents	9ad51c7bc036
children	54457678186b

rev	line source
3 9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	1 ==========================
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	2 Exception Handling in LLVM
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	3 ==========================
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	4
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	5 .. contents::
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	6 :local:
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	7
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	8 Introduction
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	9 ============
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	10
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	11 This document is the central repository for all information pertaining to
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	12 exception handling in LLVM. It describes the format that LLVM exception
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	13 handling information takes, which is useful for those interested in creating
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	14 front-ends or dealing directly with the information. Further, this document
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	15 provides specific examples of what exception handling information is used for in
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	16 C and C++.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	17
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	18 Itanium ABI Zero-cost Exception Handling
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	19 ----------------------------------------
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	20
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	21 Exception handling for most programming languages is designed to recover from
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	22 conditions that rarely occur during general use of an application. To that end,
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	23 exception handling should not interfere with the main flow of an application's
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	24 algorithm by performing checkpointing tasks, such as saving the current pc or
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	25 register state.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	26
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	27 The Itanium ABI Exception Handling Specification defines a methodology for
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	28 providing outlying data in the form of exception tables without inlining
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	29 speculative exception handling code in the flow of an application's main
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	30 algorithm. Thus, the specification is said to add "zero-cost" to the normal
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	31 execution of an application.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	32
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	33 A more complete description of the Itanium ABI exception handling runtime
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	34 support of can be found at `Itanium C++ ABI: Exception Handling
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	35 <http://mentorembedded.github.com/cxx-abi/abi-eh.html>`_. A description of the
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	36 exception frame format can be found at `Exception Frames
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	37 <http://refspecs.linuxfoundation.org/LSB_3.0.0/LSB-Core-generic/LSB-Core-generic/ehframechpt.html>`_,
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	38 with details of the DWARF 4 specification at `DWARF 4 Standard
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	39 <http://dwarfstd.org/Dwarf4Std.php>`_. A description for the C++ exception
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	40 table formats can be found at `Exception Handling Tables
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	41 <http://mentorembedded.github.com/cxx-abi/exceptions.pdf>`_.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	42
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	43 Setjmp/Longjmp Exception Handling
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	44 ---------------------------------
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	45
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	46 Setjmp/Longjmp (SJLJ) based exception handling uses LLVM intrinsics
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	47 `llvm.eh.sjlj.setjmp`_ and `llvm.eh.sjlj.longjmp`_ to handle control flow for
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	48 exception handling.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	49
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	50 For each function which does exception processing --- be it ``try``/``catch``
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	51 blocks or cleanups --- that function registers itself on a global frame
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	52 list. When exceptions are unwinding, the runtime uses this list to identify
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	53 which functions need processing.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	54
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	55 Landing pad selection is encoded in the call site entry of the function
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	56 context. The runtime returns to the function via `llvm.eh.sjlj.longjmp`_, where
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	57 a switch table transfers control to the appropriate landing pad based on the
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	58 index stored in the function context.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	59
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	60 In contrast to DWARF exception handling, which encodes exception regions and
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	61 frame information in out-of-line tables, SJLJ exception handling builds and
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	62 removes the unwind frame context at runtime. This results in faster exception
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	63 handling at the expense of slower execution when no exceptions are thrown. As
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	64 exceptions are, by their nature, intended for uncommon code paths, DWARF
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	65 exception handling is generally preferred to SJLJ.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	66
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	67 Overview
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	68 --------
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	69
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	70 When an exception is thrown in LLVM code, the runtime does its best to find a
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	71 handler suited to processing the circumstance.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	72
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	73 The runtime first attempts to find an exception frame corresponding to the
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	74 function where the exception was thrown. If the programming language supports
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	75 exception handling (e.g. C++), the exception frame contains a reference to an
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	76 exception table describing how to process the exception. If the language does
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	77 not support exception handling (e.g. C), or if the exception needs to be
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	78 forwarded to a prior activation, the exception frame contains information about
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	79 how to unwind the current activation and restore the state of the prior
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	80 activation. This process is repeated until the exception is handled. If the
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	81 exception is not handled and no activations remain, then the application is
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	82 terminated with an appropriate error message.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	83
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	84 Because different programming languages have different behaviors when handling
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	85 exceptions, the exception handling ABI provides a mechanism for
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	86 supplying personalities. An exception handling personality is defined by
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	87 way of a personality function (e.g. ``__gxx_personality_v0`` in C++),
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	88 which receives the context of the exception, an exception structure
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	89 containing the exception object type and value, and a reference to the exception
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	90 table for the current function. The personality function for the current
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	91 compile unit is specified in a common exception frame.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	92
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	93 The organization of an exception table is language dependent. For C++, an
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	94 exception table is organized as a series of code ranges defining what to do if
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	95 an exception occurs in that range. Typically, the information associated with a
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	96 range defines which types of exception objects (using C++ type info) that are
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	97 handled in that range, and an associated action that should take place. Actions
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	98 typically pass control to a landing pad.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	99
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	100 A landing pad corresponds roughly to the code found in the ``catch`` portion of
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	101 a ``try``/``catch`` sequence. When execution resumes at a landing pad, it
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	102 receives an exception structure and a selector value corresponding to the
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	103 type of exception thrown. The selector is then used to determine which catch
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	104 should actually process the exception.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	105
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	106 LLVM Code Generation
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	107 ====================
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	108
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	109 From a C++ developer's perspective, exceptions are defined in terms of the
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	110 ``throw`` and ``try``/``catch`` statements. In this section we will describe the
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	111 implementation of LLVM exception handling in terms of C++ examples.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	112
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	113 Throw
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	114 -----
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	115
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	116 Languages that support exception handling typically provide a ``throw``
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	117 operation to initiate the exception process. Internally, a ``throw`` operation
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	118 breaks down into two steps.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	119
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	120 #. A request is made to allocate exception space for an exception structure.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	121 This structure needs to survive beyond the current activation. This structure
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	122 will contain the type and value of the object being thrown.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	123
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	124 #. A call is made to the runtime to raise the exception, passing the exception
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	125 structure as an argument.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	126
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	127 In C++, the allocation of the exception structure is done by the
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	128 ``__cxa_allocate_exception`` runtime function. The exception raising is handled
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	129 by ``__cxa_throw``. The type of the exception is represented using a C++ RTTI
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	130 structure.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	131
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	132 Try/Catch
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	133 ---------
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	134
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	135 A call within the scope of a try statement can potentially raise an
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	136 exception. In those circumstances, the LLVM C++ front-end replaces the call with
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	137 an ``invoke`` instruction. Unlike a call, the ``invoke`` has two potential
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	138 continuation points:
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	139
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	140 #. where to continue when the call succeeds as per normal, and
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	141
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	142 #. where to continue if the call raises an exception, either by a throw or the
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	143 unwinding of a throw
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	144
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	145 The term used to define a the place where an ``invoke`` continues after an
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	146 exception is called a landing pad. LLVM landing pads are conceptually
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	147 alternative function entry points where an exception structure reference and a
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	148 type info index are passed in as arguments. The landing pad saves the exception
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	149 structure reference and then proceeds to select the catch block that corresponds
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	150 to the type info of the exception object.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	151
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	152 The LLVM :ref:`i_landingpad` is used to convey information about the landing
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	153 pad to the back end. For C++, the ``landingpad`` instruction returns a pointer
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	154 and integer pair corresponding to the pointer to the exception structure and
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	155 the selector value respectively.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	156
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	157 The ``landingpad`` instruction takes a reference to the personality function to
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	158 be used for this ``try``/``catch`` sequence. The remainder of the instruction is
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	159 a list of cleanup, catch, and filter clauses. The exception is tested
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	160 against the clauses sequentially from first to last. The selector value is a
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	161 positive number if the exception matched a type info, a negative number if it
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	162 matched a filter, and zero if it matched a cleanup. If nothing is matched, the
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	163 behavior of the program is `undefined`_. If a type info matched, then the
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	164 selector value is the index of the type info in the exception table, which can
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	165 be obtained using the `llvm.eh.typeid.for`_ intrinsic.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	166
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	167 Once the landing pad has the type info selector, the code branches to the code
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	168 for the first catch. The catch then checks the value of the type info selector
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	169 against the index of type info for that catch. Since the type info index is not
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	170 known until all the type infos have been gathered in the backend, the catch code
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	171 must call the `llvm.eh.typeid.for`_ intrinsic to determine the index for a given
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	172 type info. If the catch fails to match the selector then control is passed on to
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	173 the next catch.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	174
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	175 Finally, the entry and exit of catch code is bracketed with calls to
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	176 ``__cxa_begin_catch`` and ``__cxa_end_catch``.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	177
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	178 * ``__cxa_begin_catch`` takes an exception structure reference as an argument
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	179 and returns the value of the exception object.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	180
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	181 * ``__cxa_end_catch`` takes no arguments. This function:
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	182
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	183 #. Locates the most recently caught exception and decrements its handler
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	184 count,
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	185
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	186 #. Removes the exception from the caught stack if the handler count goes to
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	187 zero, and
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	188
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	189 #. Destroys the exception if the handler count goes to zero and the exception
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	190 was not re-thrown by throw.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	191
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	192 .. note::
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	193
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	194 a rethrow from within the catch may replace this call with a
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	195 ``__cxa_rethrow``.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	196
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	197 Cleanups
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	198 --------
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	199
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	200 A cleanup is extra code which needs to be run as part of unwinding a scope. C++
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	201 destructors are a typical example, but other languages and language extensions
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	202 provide a variety of different kinds of cleanups. In general, a landing pad may
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	203 need to run arbitrary amounts of cleanup code before actually entering a catch
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	204 block. To indicate the presence of cleanups, a :ref:`i_landingpad` should have
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	205 a cleanup clause. Otherwise, the unwinder will not stop at the landing pad if
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	206 there are no catches or filters that require it to.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	207
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	208 .. note::
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	209
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	210 Do not allow a new exception to propagate out of the execution of a
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	211 cleanup. This can corrupt the internal state of the unwinder. Different
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	212 languages describe different high-level semantics for these situations: for
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	213 example, C++ requires that the process be terminated, whereas Ada cancels both
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	214 exceptions and throws a third.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	215
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	216 When all cleanups are finished, if the exception is not handled by the current
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	217 function, resume unwinding by calling the `resume
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	218 instruction <LangRef.html#i_resume>`_, passing in the result of the
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	219 ``landingpad`` instruction for the original landing pad.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	220
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	221 Throw Filters
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	222 -------------
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	223
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	224 C++ allows the specification of which exception types may be thrown from a
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	225 function. To represent this, a top level landing pad may exist to filter out
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	226 invalid types. To express this in LLVM code the :ref:`i_landingpad` will have a
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	227 filter clause. The clause consists of an array of type infos.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	228 ``landingpad`` will return a negative value
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	229 if the exception does not match any of the type infos. If no match is found then
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	230 a call to ``__cxa_call_unexpected`` should be made, otherwise
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	231 ``_Unwind_Resume``. Each of these functions requires a reference to the
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	232 exception structure. Note that the most general form of a ``landingpad``
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	233 instruction can have any number of catch, cleanup, and filter clauses (though
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	234 having more than one cleanup is pointless). The LLVM C++ front-end can generate
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	235 such ``landingpad`` instructions due to inlining creating nested exception
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	236 handling scopes.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	237
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	238 .. _undefined:
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	239
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	240 Restrictions
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	241 ------------
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	242
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	243 The unwinder delegates the decision of whether to stop in a call frame to that
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	244 call frame's language-specific personality function. Not all unwinders guarantee
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	245 that they will stop to perform cleanups. For example, the GNU C++ unwinder
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	246 doesn't do so unless the exception is actually caught somewhere further up the
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	247 stack.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	248
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	249 In order for inlining to behave correctly, landing pads must be prepared to
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	250 handle selector results that they did not originally advertise. Suppose that a
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	251 function catches exceptions of type ``A``, and it's inlined into a function that
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	252 catches exceptions of type ``B``. The inliner will update the ``landingpad``
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	253 instruction for the inlined landing pad to include the fact that ``B`` is also
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	254 caught. If that landing pad assumes that it will only be entered to catch an
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	255 ``A``, it's in for a rude awakening. Consequently, landing pads must test for
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	256 the selector results they understand and then resume exception propagation with
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	257 the `resume instruction <LangRef.html#i_resume>`_ if none of the conditions
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	258 match.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	259
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	260 Exception Handling Intrinsics
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	261 =============================
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	262
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	263 In addition to the ``landingpad`` and ``resume`` instructions, LLVM uses several
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	264 intrinsic functions (name prefixed with ``llvm.eh``) to provide exception
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	265 handling information at various points in generated code.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	266
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	267 .. _llvm.eh.typeid.for:
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	268
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	269 ``llvm.eh.typeid.for``
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	270 ----------------------
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	271
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	272 .. code-block:: llvm
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	273
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	274 i32 @llvm.eh.typeid.for(i8* %type_info)
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	275
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	276
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	277 This intrinsic returns the type info index in the exception table of the current
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	278 function. This value can be used to compare against the result of
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	279 ``landingpad`` instruction. The single argument is a reference to a type info.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	280
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	281 .. _llvm.eh.sjlj.setjmp:
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	282
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	283 ``llvm.eh.sjlj.setjmp``
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	284 -----------------------
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	285
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	286 .. code-block:: llvm
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	287
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	288 i32 @llvm.eh.sjlj.setjmp(i8* %setjmp_buf)
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	289
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	290 For SJLJ based exception handling, this intrinsic forces register saving for the
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	291 current function and stores the address of the following instruction for use as
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	292 a destination address by `llvm.eh.sjlj.longjmp`_. The buffer format and the
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	293 overall functioning of this intrinsic is compatible with the GCC
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	294 ``__builtin_setjmp`` implementation allowing code built with the clang and GCC
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	295 to interoperate.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	296
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	297 The single parameter is a pointer to a five word buffer in which the calling
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	298 context is saved. The front end places the frame pointer in the first word, and
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	299 the target implementation of this intrinsic should place the destination address
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	300 for a `llvm.eh.sjlj.longjmp`_ in the second word. The following three words are
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	301 available for use in a target-specific manner.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	302
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	303 .. _llvm.eh.sjlj.longjmp:
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	304
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	305 ``llvm.eh.sjlj.longjmp``
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	306 ------------------------
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	307
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	308 .. code-block:: llvm
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	309
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	310 void @llvm.eh.sjlj.longjmp(i8* %setjmp_buf)
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	311
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	312 For SJLJ based exception handling, the ``llvm.eh.sjlj.longjmp`` intrinsic is
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	313 used to implement ``__builtin_longjmp()``. The single parameter is a pointer to
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	314 a buffer populated by `llvm.eh.sjlj.setjmp`_. The frame pointer and stack
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	315 pointer are restored from the buffer, then control is transferred to the
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	316 destination address.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	317
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	318 ``llvm.eh.sjlj.lsda``
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	319 ---------------------
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	320
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	321 .. code-block:: llvm
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	322
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	323 i8* @llvm.eh.sjlj.lsda()
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	324
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	325 For SJLJ based exception handling, the ``llvm.eh.sjlj.lsda`` intrinsic returns
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	326 the address of the Language Specific Data Area (LSDA) for the current
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	327 function. The SJLJ front-end code stores this address in the exception handling
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	328 function context for use by the runtime.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	329
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	330 ``llvm.eh.sjlj.callsite``
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	331 -------------------------
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	332
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	333 .. code-block:: llvm
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	334
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	335 void @llvm.eh.sjlj.callsite(i32 %call_site_num)
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	336
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	337 For SJLJ based exception handling, the ``llvm.eh.sjlj.callsite`` intrinsic
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	338 identifies the callsite value associated with the following ``invoke``
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	339 instruction. This is used to ensure that landing pad entries in the LSDA are
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	340 generated in matching order.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	341
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	342 Asm Table Formats
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	343 =================
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	344
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	345 There are two tables that are used by the exception handling runtime to
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	346 determine which actions should be taken when an exception is thrown.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	347
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	348 Exception Handling Frame
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	349 ------------------------
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	350
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	351 An exception handling frame ``eh_frame`` is very similar to the unwind frame
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	352 used by DWARF debug info. The frame contains all the information necessary to
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	353 tear down the current frame and restore the state of the prior frame. There is
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	354 an exception handling frame for each function in a compile unit, plus a common
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	355 exception handling frame that defines information common to all functions in the
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	356 unit.
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	357
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	358 Exception Tables
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	359 ----------------
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	360
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	361 An exception table contains information about what actions to take when an
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	362 exception is thrown in a particular part of a function's code. There is one
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	363 exception table per function, except leaf functions and functions that have
9ad51c7bc036 1st commit. remove git dir and add all files. Kaito Tokumori <e105711@ie.u-ryukyu.ac.jp> parents: diff changeset	364 calls only to non-throwing functions. They do not need an exception table.

Mercurial > hg > Members > tobaru > cbc > CbC_llvm

annotate docs/ExceptionHandling.rst @ 16:d405342cecb1