[lld] r299528 - [ELF] - Define __bss_start symbol.
George Rimar via llvm-commits
llvm-commits at lists.llvm.org
Wed Apr 5 03:03:26 PDT 2017
Author: grimar
Date: Wed Apr 5 05:03:25 2017
New Revision: 299528
URL: http://llvm.org/viewvc/llvm-project?rev=299528&view=rev
Log:
[ELF] - Define __bss_start symbol.
GNU linkers define __bss_start symbol.
Patch teaches LLD to do that. This is PR32051.
Below is part of standart ld.bfd script:
.data1 : { *(.data1) }
_edata = .; PROVIDE (edata = .);
. = .;
__bss_start = .;
.bss :
{
Currently LLD can emit up to 3 .bss* sections as one of testcase shows.
Implementation inserts this symbol before first .bss* output section.
Differential revision: https://reviews.llvm.org/D30419
Added:
lld/trunk/test/ELF/bss-start-common.s
Modified:
lld/trunk/ELF/Symbols.cpp
lld/trunk/ELF/Symbols.h
lld/trunk/ELF/Writer.cpp
Modified: lld/trunk/ELF/Symbols.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Symbols.cpp?rev=299528&r1=299527&r2=299528&view=diff
==============================================================================
--- lld/trunk/ELF/Symbols.cpp (original)
+++ lld/trunk/ELF/Symbols.cpp Wed Apr 5 05:03:25 2017
@@ -28,6 +28,7 @@ using namespace llvm::ELF;
using namespace lld;
using namespace lld::elf;
+DefinedRegular *ElfSym::Bss;
DefinedRegular *ElfSym::Etext;
DefinedRegular *ElfSym::Etext2;
DefinedRegular *ElfSym::Edata;
Modified: lld/trunk/ELF/Symbols.h
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Symbols.h?rev=299528&r1=299527&r2=299528&view=diff
==============================================================================
--- lld/trunk/ELF/Symbols.h (original)
+++ lld/trunk/ELF/Symbols.h Wed Apr 5 05:03:25 2017
@@ -302,6 +302,9 @@ public:
// Some linker-generated symbols need to be created as
// DefinedRegular symbols.
struct ElfSym {
+ // The content for __bss_start symbol.
+ static DefinedRegular *Bss;
+
// The content for _etext and etext symbols.
static DefinedRegular *Etext;
static DefinedRegular *Etext2;
Modified: lld/trunk/ELF/Writer.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Writer.cpp?rev=299528&r1=299527&r2=299528&view=diff
==============================================================================
--- lld/trunk/ELF/Writer.cpp (original)
+++ lld/trunk/ELF/Writer.cpp Wed Apr 5 05:03:25 2017
@@ -846,6 +846,10 @@ template <class ELFT> void Writer<ELFT>:
// __ehdr_start is the location of ELF file headers.
addOptionalRegular<ELFT>("__ehdr_start", Out::ElfHeader, 0, STV_HIDDEN);
+ // __bss_start is the location of .bss section.
+ ElfSym::Bss =
+ addOptionalRegular<ELFT>("__bss_start", Out::ElfHeader, 0, STV_DEFAULT);
+
auto Define = [](StringRef S, DefinedRegular *&Sym1, DefinedRegular *&Sym2) {
Sym1 = addOptionalRegular<ELFT>(S, Out::ElfHeader, 0, STV_DEFAULT);
assert(S.startswith("_"));
@@ -1675,6 +1679,9 @@ template <class ELFT> void Writer<ELFT>:
if (LastRW)
Set(ElfSym::Edata, ElfSym::Edata2, LastRW->First, LastRW->p_filesz);
+ if (ElfSym::Bss)
+ ElfSym::Bss->Section = findSection(".bss");
+
// Setup MIPS _gp_disp/__gnu_local_gp symbols which should
// be equal to the _gp symbol's value.
if (Config->EMachine == EM_MIPS) {
Added: lld/trunk/test/ELF/bss-start-common.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/bss-start-common.s?rev=299528&view=auto
==============================================================================
--- lld/trunk/test/ELF/bss-start-common.s (added)
+++ lld/trunk/test/ELF/bss-start-common.s Wed Apr 5 05:03:25 2017
@@ -0,0 +1,15 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
+# RUN: ld.lld %t -o %t2
+# RUN: llvm-objdump -t -section-headers %t2 | FileCheck %s
+
+# CHECK: Sections:
+# CHECK: Idx Name Size Address Type
+# CHECK: 2 .bss 00000004 0000000000201000 BSS
+# CHECK: SYMBOL TABLE:
+# CHECK: 0000000000201000 .bss 00000000 __bss_start
+
+.global __bss_start
+.text
+_start:
+.comm sym1,4,4
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