[PATCH] D30419: [ELF] - Define __bss_start symbol.

[George Rimar via Phabricator via llvm-commits]

grimar updated this revision to Diff 94054.
grimar added a comment.

- Addressed review comments.


https://reviews.llvm.org/D30419

Files:
  ELF/Symbols.cpp
  ELF/Symbols.h
  ELF/Writer.cpp
  test/ELF/bss-start-common.s


Index: test/ELF/bss-start-common.s
===================================================================
--- test/ELF/bss-start-common.s
+++ test/ELF/bss-start-common.s
@@ -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
Index: ELF/Writer.cpp
===================================================================
--- ELF/Writer.cpp
+++ ELF/Writer.cpp
@@ -846,6 +846,10 @@
   // __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.* sections.
+  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 @@
   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) {
Index: ELF/Symbols.h
===================================================================
--- ELF/Symbols.h
+++ ELF/Symbols.h
@@ -302,6 +302,9 @@
 // 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;
Index: ELF/Symbols.cpp
===================================================================
--- ELF/Symbols.cpp
+++ ELF/Symbols.cpp
@@ -28,6 +28,7 @@
 using namespace lld;
 using namespace lld::elf;
 
+DefinedRegular *ElfSym::Bss;
 DefinedRegular *ElfSym::Etext;
 DefinedRegular *ElfSym::Etext2;
 DefinedRegular *ElfSym::Edata;


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