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Lots of blocks had "llvm" or "nasm" syntax types but either weren't following the syntax, or the syntax has changed (and sphinx hasn't keep up) or the type doesn't even exist (nasm?). Other documents had :options: what were invalid. I only removed those that had warnings, and left the ones that didn't, in order to follow the principle of least surprise. This is like this for ages, but the buildbot is now failing on errors. It may take a while to upgrade the buildbot's sphinx, if that's even possible, but that shouldn't stop us from getting docs updates (which seem down for quite a while). Also, we're not losing any syntax highlight, since when it doesn't parse, it doesn't colour. Ie. those blocks are not being highlighted anyway. I'm trying to get all docs in one go, so that it's easy to revert later if we do fix, or at least easy to know what's to fix. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@276109 91177308-0d34-0410-b5e6-96231b3b80d8
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===============
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LLVM Extensions
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===============
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.. contents::
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:local:
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.. toctree::
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:hidden:
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Introduction
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============
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This document describes extensions to tools and formats LLVM seeks compatibility
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with.
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General Assembly Syntax
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===========================
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C99-style Hexadecimal Floating-point Constants
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----------------------------------------------
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LLVM's assemblers allow floating-point constants to be written in C99's
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hexadecimal format instead of decimal if desired.
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.. code-block:: gas
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.section .data
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.float 0x1c2.2ap3
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Machine-specific Assembly Syntax
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================================
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X86/COFF-Dependent
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------------------
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Relocations
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^^^^^^^^^^^
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The following additional relocation types are supported:
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**@IMGREL** (AT&T syntax only) generates an image-relative relocation that
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corresponds to the COFF relocation types ``IMAGE_REL_I386_DIR32NB`` (32-bit) or
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``IMAGE_REL_AMD64_ADDR32NB`` (64-bit).
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.. code-block:: text
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.text
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fun:
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mov foo@IMGREL(%ebx, %ecx, 4), %eax
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.section .pdata
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.long fun@IMGREL
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.long (fun@imgrel + 0x3F)
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.long $unwind$fun@imgrel
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**.secrel32** generates a relocation that corresponds to the COFF relocation
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types ``IMAGE_REL_I386_SECREL`` (32-bit) or ``IMAGE_REL_AMD64_SECREL`` (64-bit).
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**.secidx** relocation generates an index of the section that contains
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the target. It corresponds to the COFF relocation types
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``IMAGE_REL_I386_SECTION`` (32-bit) or ``IMAGE_REL_AMD64_SECTION`` (64-bit).
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.. code-block:: gas
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.section .debug$S,"rn"
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.long 4
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.long 242
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.long 40
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.secrel32 _function_name
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.secidx _function_name
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...
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``.linkonce`` Directive
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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Syntax:
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``.linkonce [ comdat type ]``
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Supported COMDAT types:
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``discard``
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Discards duplicate sections with the same COMDAT symbol. This is the default
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if no type is specified.
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``one_only``
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If the symbol is defined multiple times, the linker issues an error.
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``same_size``
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Duplicates are discarded, but the linker issues an error if any have
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different sizes.
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``same_contents``
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Duplicates are discarded, but the linker issues an error if any duplicates
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do not have exactly the same content.
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``largest``
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Links the largest section from among the duplicates.
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``newest``
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Links the newest section from among the duplicates.
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.. code-block:: gas
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.section .text$foo
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.linkonce
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...
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``.section`` Directive
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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MC supports passing the information in ``.linkonce`` at the end of
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``.section``. For example, these two codes are equivalent
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.. code-block:: gas
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.section secName, "dr", discard, "Symbol1"
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.globl Symbol1
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Symbol1:
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.long 1
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.. code-block:: gas
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.section secName, "dr"
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.linkonce discard
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.globl Symbol1
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Symbol1:
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.long 1
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Note that in the combined form the COMDAT symbol is explicit. This
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extension exists to support multiple sections with the same name in
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different COMDATs:
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.. code-block:: gas
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.section secName, "dr", discard, "Symbol1"
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.globl Symbol1
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Symbol1:
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.long 1
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.section secName, "dr", discard, "Symbol2"
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.globl Symbol2
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Symbol2:
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.long 1
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In addition to the types allowed with ``.linkonce``, ``.section`` also accepts
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``associative``. The meaning is that the section is linked if a certain other
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COMDAT section is linked. This other section is indicated by the comdat symbol
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in this directive. It can be any symbol defined in the associated section, but
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is usually the associated section's comdat.
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The following restrictions apply to the associated section:
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1. It must be a COMDAT section.
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2. It cannot be another associative COMDAT section.
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In the following example the symobl ``sym`` is the comdat symbol of ``.foo``
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and ``.bar`` is associated to ``.foo``.
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.. code-block:: gas
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.section .foo,"bw",discard, "sym"
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.section .bar,"rd",associative, "sym"
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ELF-Dependent
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-------------
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``.section`` Directive
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^^^^^^^^^^^^^^^^^^^^^^
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In order to support creating multiple sections with the same name and comdat,
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it is possible to add an unique number at the end of the ``.seciton`` directive.
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For example, the following code creates two sections named ``.text``.
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.. code-block:: gas
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.section .text,"ax",@progbits,unique,1
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nop
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.section .text,"ax",@progbits,unique,2
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nop
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The unique number is not present in the resulting object at all. It is just used
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in the assembler to differentiate the sections.
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Target Specific Behaviour
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=========================
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Windows on ARM
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--------------
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Stack Probe Emission
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^^^^^^^^^^^^^^^^^^^^
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The reference implementation (Microsoft Visual Studio 2012) emits stack probes
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in the following fashion:
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.. code-block:: gas
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movw r4, #constant
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bl __chkstk
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sub.w sp, sp, r4
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However, this has the limitation of 32 MiB (±16MiB). In order to accommodate
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larger binaries, LLVM supports the use of ``-mcode-model=large`` to allow a 4GiB
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range via a slight deviation. It will generate an indirect jump as follows:
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.. code-block:: gas
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movw r4, #constant
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movw r12, :lower16:__chkstk
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movt r12, :upper16:__chkstk
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blx r12
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sub.w sp, sp, r4
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Variable Length Arrays
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^^^^^^^^^^^^^^^^^^^^^^
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The reference implementation (Microsoft Visual Studio 2012) does not permit the
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emission of Variable Length Arrays (VLAs).
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The Windows ARM Itanium ABI extends the base ABI by adding support for emitting
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a dynamic stack allocation. When emitting a variable stack allocation, a call
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to ``__chkstk`` is emitted unconditionally to ensure that guard pages are setup
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properly. The emission of this stack probe emission is handled similar to the
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standard stack probe emission.
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The MSVC environment does not emit code for VLAs currently.
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