[lld] r259781 - [ELF][MIPS] Add handling for __gnu_local_gp symbol

[Simon Atanasyan via llvm-commits]

Author: atanasyan
Date: Thu Feb  4 06:09:49 2016
New Revision: 259781

URL: http://llvm.org/viewvc/llvm-project?rev=259781&view=rev
Log:
[ELF][MIPS] Add handling for __gnu_local_gp symbol

This symbol is a "fake" symbol like "_gp_disp" and denotes
the GOT + 0x7FF0 value.

Added:
    lld/trunk/test/ELF/mips-gp-local.s
Modified:
    lld/trunk/ELF/Config.h
    lld/trunk/ELF/Driver.cpp
    lld/trunk/ELF/InputSection.cpp
    lld/trunk/ELF/Writer.cpp

Modified: lld/trunk/ELF/Config.h
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Config.h?rev=259781&r1=259780&r2=259781&view=diff
==============================================================================
--- lld/trunk/ELF/Config.h (original)
+++ lld/trunk/ELF/Config.h Thu Feb  4 06:09:49 2016
@@ -37,6 +37,7 @@ enum ELFKind {
 struct Configuration {
   SymbolBody *EntrySym = nullptr;
   SymbolBody *MipsGpDisp = nullptr;
+  SymbolBody *MipsLocalGp = nullptr;
   InputFile *FirstElf = nullptr;
   llvm::StringRef DynamicLinker;
   llvm::StringRef Entry;

Modified: lld/trunk/ELF/Driver.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Driver.cpp?rev=259781&r1=259780&r2=259781&view=diff
==============================================================================
--- lld/trunk/ELF/Driver.cpp (original)
+++ lld/trunk/ELF/Driver.cpp Thu Feb  4 06:09:49 2016
@@ -328,6 +328,7 @@ template <class ELFT> void LinkerDriver:
     // start of function and gp pointer into GOT. Use 'strong' variant of
     // the addIgnored to prevent '_gp_disp' substitution.
     Config->MipsGpDisp = Symtab.addIgnored("_gp_disp");
+    Config->MipsLocalGp = Symtab.addIgnored("__gnu_local_gp");
 
     // Define _gp for MIPS. st_value of _gp symbol will be updated by Writer
     // so that it points to an absolute address which is relative to GOT.

Modified: lld/trunk/ELF/InputSection.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/InputSection.cpp?rev=259781&r1=259780&r2=259781&view=diff
==============================================================================
--- lld/trunk/ELF/InputSection.cpp (original)
+++ lld/trunk/ELF/InputSection.cpp Thu Feb  4 06:09:49 2016
@@ -234,6 +234,8 @@ void InputSectionBase<ELFT>::relocate(ui
         SymVA = getMipsGpAddr<ELFT>() - AddrLoc;
       else if (Type == R_MIPS_LO16 && Body == Config->MipsGpDisp)
         SymVA = getMipsGpAddr<ELFT>() - AddrLoc + 4;
+      else if (Body == Config->MipsLocalGp)
+        SymVA = getMipsGpAddr<ELFT>();
     }
     uintX_t Size = Body->getSize<ELFT>();
     Target->relocateOne(BufLoc, BufEnd, Type, AddrLoc, SymVA + A, Size + A,

Modified: lld/trunk/ELF/Writer.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Writer.cpp?rev=259781&r1=259780&r2=259781&view=diff
==============================================================================
--- lld/trunk/ELF/Writer.cpp (original)
+++ lld/trunk/ELF/Writer.cpp Thu Feb  4 06:09:49 2016
@@ -388,7 +388,7 @@ void Writer<ELFT>::scanRelocs(
         // relocation too because that case is possible for executable file
         // linking only.
         continue;
-      if (Body == Config->MipsGpDisp)
+      if (Body == Config->MipsGpDisp || Body == Config->MipsLocalGp)
         // MIPS _gp_disp designates offset between start of function and gp
         // pointer into GOT therefore any relocations against it do not require
         // dynamic relocation.

Added: lld/trunk/test/ELF/mips-gp-local.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/mips-gp-local.s?rev=259781&view=auto
==============================================================================
--- lld/trunk/test/ELF/mips-gp-local.s (added)
+++ lld/trunk/test/ELF/mips-gp-local.s Thu Feb  4 06:09:49 2016
@@ -0,0 +1,20 @@
+# Check handling of relocations against __gnu_local_gp symbol.
+
+# RUN: llvm-mc -filetype=obj -triple=mips-unknown-linux %s -o %t.o
+# RUN: ld.lld -o %t.exe %t.o
+# RUN: llvm-objdump -d -t %t.exe | FileCheck %s
+
+# REQUIRES: mips
+
+# CHECK:      Disassembly of section .text:
+# CHECK-NEXT: __start:
+# CHECK-NEXT:    20000:  3c 08 00 00  lui   $8, 0
+# CHECK-NEXT:    20004:  21 08 00 00  addi  $8, $8, 0
+
+# CHECK: 00000000  *ABS*  00000000 _gp
+
+  .text
+  .globl  __start
+__start:
+  lui    $t0,%hi(__gnu_local_gp)
+  addi   $t0,$t0,%lo(__gnu_local_gp)