1 =============== 2 LLVM Extensions 3 =============== 4 5 .. contents:: 6 :local: 7 8 .. toctree:: 9 :hidden: 10 11 Introduction 12 ============ 13 14 This document describes extensions to tools and formats LLVM seeks compatibility 15 with. 16 17 Machine-specific Assembly Syntax 18 ================================ 19 20 X86/COFF-Dependent 21 ------------------ 22 23 Relocations 24 ^^^^^^^^^^^ 25 26 The following additional relocation type is supported: 27 28 **@IMGREL** (AT&T syntax only) generates an image-relative relocation that 29 corresponds 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 47 Syntax: 48 49 ``.linkonce [ comdat type [ section identifier ] ]`` 50 51 Supported 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
