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72935dd909
This is the first step to fix pr17918. It extends the .section directive a bit, inspired by what the ELF one looks like. The problem with using linkonce is that given .section foo .linkonce.... .section foo .linkonce we would already have switched sections when getting to .linkonce. The cleanest solution seems to be to add the comdat information in the .section itself. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@195148 91177308-0d34-0410-b5e6-96231b3b80d8
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3.1 KiB
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146 lines
3.1 KiB
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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 type is 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:: gas
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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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``.linkonce`` Directive
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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Syntax:
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``.linkonce [ comdat type [ section identifier ] ]``
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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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``associative``
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Links the section if a certain other COMDAT section is linked. This other
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section is indicated by its section identifier following the comdat type.
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The following restrictions apply to the associated section:
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1. It must be the name of a section already defined.
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2. It must differ from the current section.
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3. It must be a COMDAT section.
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4. It cannot be another associative COMDAT section.
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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$foo
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.linkonce
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...
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.section .xdata$foo
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.linkonce associative .text$foo
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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 explict. This
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extension exits 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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