[lld] r265784 - [lld] [ELF/AARCH64] Fix dynamic relocation from PIC GOT access

[Adhemerval Zanella via llvm-commits]

Author: azanella
Date: Fri Apr  8 09:10:41 2016
New Revision: 265784

URL: http://llvm.org/viewvc/llvm-project?rev=265784&view=rev
Log:
[lld] [ELF/AARCH64] Fix dynamic relocation from PIC GOT access

This patch fixes dynamic relocation creation from GOT access in dynamic
objects on aarch64. Current code creates a plt relative one
(R_AARCH64_JUMP_SLOT) instead of a got relative (R_AARCH64_GLOB_DAT).

It leads the programs fails with:

$ cat t.cc

std::string test = "hello...\n";

int main ()
{
  printf ("%s\n", test.c_str());
  return 0;
}
$ clang++ t.cc -fpic -o t
$ ./t
hello...

Segmentation fault (core dumped)

Due the fact it will try to access the plt instead of the got for
__cxa_atexit registration for the std::string destruction.  It will
lead in a bogus function address in atexit.

Added:
    lld/trunk/test/ELF/aarch64-fpic-got.s
Modified:
    lld/trunk/ELF/Target.cpp

Modified: lld/trunk/ELF/Target.cpp
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/ELF/Target.cpp?rev=265784&r1=265783&r2=265784&view=diff
==============================================================================
--- lld/trunk/ELF/Target.cpp (original)
+++ lld/trunk/ELF/Target.cpp Fri Apr  8 09:10:41 2016
@@ -170,6 +170,7 @@ public:
   bool isRelRelative(uint32_t Type) const override;
   bool needsCopyRelImpl(uint32_t Type) const override;
   bool needsGot(uint32_t Type, const SymbolBody &S) const override;
+  bool refersToGotEntry(uint32_t Type) const override;
   bool needsPltImpl(uint32_t Type) const override;
   void relocateOne(uint8_t *Loc, uint8_t *BufEnd, uint32_t Type, uint64_t P,
                    uint64_t SA) const override;
@@ -1381,6 +1382,10 @@ bool AArch64TargetInfo::needsGot(uint32_
   }
 }
 
+bool AArch64TargetInfo::refersToGotEntry(uint32_t Type) const {
+  return Type == R_AARCH64_ADR_GOT_PAGE || Type == R_AARCH64_LD64_GOT_LO12_NC;
+}
+
 bool AArch64TargetInfo::needsPltImpl(uint32_t Type) const {
   switch (Type) {
   default:

Added: lld/trunk/test/ELF/aarch64-fpic-got.s
URL: http://llvm.org/viewvc/llvm-project/lld/trunk/test/ELF/aarch64-fpic-got.s?rev=265784&view=auto
==============================================================================
--- lld/trunk/test/ELF/aarch64-fpic-got.s (added)
+++ lld/trunk/test/ELF/aarch64-fpic-got.s Fri Apr  8 09:10:41 2016
@@ -0,0 +1,18 @@
+# REQUIRES: aarch64
+
+# RUN: llvm-mc -filetype=obj -triple=aarch64-none-linux %s -o %t.o
+# RUN: llvm-mc -filetype=obj -triple=aarch64-none-linux %p/Inputs/shared.s -o %t-lib.o
+# RUN: ld.lld -shared %t-lib.o -o %t-lib.so
+# RUN: ld.lld %t-lib.so %t.o -o %t.exe
+# RUN: llvm-readobj -dyn-relocations %t.exe | FileCheck %s
+
+## Checks if got access to dynamic objects is done through a got relative
+## dynamic relocation and not using plt relative (R_AARCH64_JUMP_SLOT).
+# CHECK:       Dynamic Relocations {
+# CHECK-NEXT:    0x{{[0-9A-F]+}}  R_AARCH64_GLOB_DAT bar 0x0
+# CHECK-NEXT:  }
+
+.globl _start
+_start:
+  adrp x0, :got:bar
+  ldr  x0, [x0, :got_lo12:bar]