From 6bf4da02c13673bfd34f447a4b8a68905e05dea7 Mon Sep 17 00:00:00 2001 From: Adhemerval Zanella Date: Mon, 27 Apr 2015 13:55:14 +0000 Subject: ELF/ARM: Ignore R_ARM_V4BX for ARMv4 but allow linking This patch allow the ARM relocation R_ARM_V4BX to be processed by lld, although it is not really handled in the static relocation code. The relocation is in the form: Relocation section '.rel.text' at offset 0x428 contains 4 entries: Offset Info Type Sym.Value Sym. Name 00000014 00000028 R_ARM_V4BX Meaning it does have a direct target, but rather references to an absolute section *ABS* (in this exemple to the .text segment itself). It makes the target Atom after file parse to not have a associated pointer and thus generating a derrefence NULL point in ELFFile::findAtom. Current approach is just ignore and return nullptr in such cases. The problem relies that default GCC configuration for arm-linux-gnueabi{hf} emits the relocation for the asm: -- .syntax unified .arm .p2align 2 .type fn, %function fn: ldr r3, .LGOT ldr r2, .LGOT+4 .LPIC: add r3, pc, r3 ldr r2, [r3, r2] cmp r2, #0 bxeq lr b __start__ .LGOT: .word _GLOBAL_OFFSET_TABLE_-(.LPIC+8) .word __start__(GOT) -- But only with the option -march=armv4 (which is the default GCC configuration). For arm5 and forward the relocation is not created. This a special relocation (defined miscellaneous for ARM) that instruct the linker to replace the bx instruction into a mov. GNU linker has some options related to which substitution it can create for such cases. With this patch I can dynamically link an application against a GLIBC arm-linux-gnueabi system configured with default GCC. llvm-svn: 235880 --- lld/lib/ReaderWriter/ELF/ELFFile.cpp | 5 +++++ 1 file changed, 5 insertions(+) (limited to 'lld/lib/ReaderWriter/ELF/ELFFile.cpp') diff --git a/lld/lib/ReaderWriter/ELF/ELFFile.cpp b/lld/lib/ReaderWriter/ELF/ELFFile.cpp index ab2ec605687..57c25038eda 100644 --- a/lld/lib/ReaderWriter/ELF/ELFFile.cpp +++ b/lld/lib/ReaderWriter/ELF/ELFFile.cpp @@ -38,6 +38,11 @@ Atom *ELFFile::findAtom(const Elf_Sym *sourceSym, const Elf_Sym *targetSym) { // Return the atom for targetSym if we can do so. Atom *target = _symbolToAtomMapping.lookup(targetSym); + if (!target) + // Some realocations (R_ARM_V4BX) do not have a defined + // target. For this cases make it points to itself. + target = _symbolToAtomMapping.lookup(sourceSym); + if (target->definition() != Atom::definitionRegular) return target; Atom::Scope scope = llvm::cast(target)->scope(); -- cgit v1.2.3