replica
/
hanchenye-llvm-project
2
0
Fork 0
Code Issues Pull Requests Projects Releases Wiki Activity

[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

llvm-svn: 299528
This commit is contained in:
George Rimar 2017-04-05 10:03:25 +00:00
parent d5be88ecf8
commit e6c5d3862d
4 changed files with 26 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
lld/ELF/Symbols.cpp
View File

@ -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;

3
lld/ELF/Symbols.h
View File

@ -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;

7
lld/ELF/Writer.cpp
View File

@ -846,6 +846,10 @@ template <class ELFT> void Writer<ELFT>::addReservedSymbols() {
// __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>::fixPredefinedSymbols() {
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) {

15
lld/test/ELF/bss-start-common.s Normal file
View File

@ -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