1===============
2LLVM Extensions
3===============
4
5.. contents::
6   :local:
7
8.. toctree::
9   :hidden:
10
11Introduction
12============
13
14This document describes extensions to tools and formats LLVM seeks compatibility
15with.
16
17Machine-specific Assembly Syntax
18================================
19
20X86/COFF-Dependent
21------------------
22
23Relocations
24^^^^^^^^^^^
25
26The following additional relocation type is supported:
27
28**@IMGREL** (AT&T syntax only) generates an image-relative relocation that
29corresponds to the COFF relocation types ``IMAGE_REL_I386_DIR32NB`` (32-bit) or
30``IMAGE_REL_AMD64_ADDR32NB`` (64-bit).
31
32.. code-block:: gas
33
34  .text
35  fun:
36    mov foo@IMGREL(%ebx, %ecx, 4), %eax
37
38  .section .pdata
39    .long fun@IMGREL
40    .long (fun@imgrel + 0x3F)
41    .long $unwind$fun@imgrel
42
43
44``.linkonce`` Directive
45^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
46
47Syntax:
48
49   ``.linkonce [ comdat type [ section identifier ] ]``
50
51Supported COMDAT types:
52
53``discard``
54   Discards duplicate sections with the same COMDAT symbol. This is the default
55   if no type is specified.
56
57``one_only``
58   If the symbol is defined multiple times, the linker issues an error.
59
60``same_size``
61   Duplicates are discarded, but the linker issues an error if any have
62   different sizes.
63
64``same_contents``
65   Duplicates are discarded, but the linker issues an error if any duplicates
66   do not have exactly the same content.
67
68``associative``
69   Links the section if a certain other COMDAT section is linked. This other
70   section is indicated by its section identifier following the comdat type.
71   The following restrictions apply to the associated section:
72
73   1. It must be the name of a section already defined.
74   2. It must differ from the current section.
75   3. It must be a COMDAT section.
76   4. It cannot be another associative COMDAT section.
77
78``largest``
79   Links the largest section from among the duplicates.
80
81``newest``
82   Links the newest section from among the duplicates.
83
84
85.. code-block:: gas
86
87  .section .text$foo
88  .linkonce
89    ...
90
91  .section .xdata$foo
92  .linkonce associative .text$foo
93    ...
94