[ELF2] - fix for using PLT/GOT for X86TargetInfo

[grimar]

Summary

I noticed that functions from DSO looks to be always called via PLT+GOT on elf32-i386 linked with modern ld. I think the same approach as was used in X86_64TargetInfo::relocNeedsPlt() should be applied here.

I took the object file and dso from relocation-i686.s test and linked them to executable:

ld --emit-relocs -melf_i386 tmain.o tshared.so -o tmain

And found that .dynamic_reloc section has calls to PLT.

Disassembly of section .dynamic_reloc:
08048199 <.dynamic_reloc>:
8048199: e8 d6 ff ff ff call 8048174 <bar@plt+0x4>

So this fix makes the behavior to be consistent with ld.

[ruiu]

LGTM with a nit.

ELF/Target.cpp

59–66 ↗

(On Diff #36768)

return Type == R_386_PLT32 || (Type == R_386_PC32 && S.isShared());

lld/trunk/ELF/Target.cpp

bool X86TargetInfo::relocNeedsGot(uint32_t Type, const SymbolBody &S) const {
   return Type == R_386_GOT32 || relocNeedsPlt(Type, S);
 }
 
 bool X86TargetInfo::relocPointsToGot(uint32_t Type) const {
   return Type == R_386_GOTPC;
 }
 
 bool X86TargetInfo::relocNeedsPlt(uint32_t Type, const SymbolBody &S) const {
-  return Type == R_386_PLT32;
+  return Type == R_386_PLT32 || (Type == R_386_PC32 && S.isShared());
 }
 
 static void add32le(uint8_t *L, int32_t V) { write32le(L, read32le(L) + V); }
 static void or16le(uint8_t *L, int16_t V) { write16le(L, read16le(L) | V); }
 static void or32le(uint8_t *L, int32_t V) { write32le(L, read32le(L) | V); }
 static void or64le(uint8_t *L, int64_t V) { write64le(L, read64le(L) | V); }
 
 void X86TargetInfo::relocateOne(uint8_t *Buf, const void *RelP, uint32_t Type,

lld/trunk/test/elf2/relocation-i686.s

 // CHECK:      Disassembly of section .R_386_GOTPC:
 // CHECK-NEXT: R_386_GOTPC:
 // CHECK-NEXT:   12014:  {{.*}} movl  $4156, %eax
 
 .section .dynamic_reloc, "ax",@progbits
         call bar+4
 // CHECK:      Disassembly of section .dynamic_reloc:
 // CHECK-NEXT: .dynamic_reloc:
-// CHECK-NEXT:   12019:  e8 00 00 00 00  calll  0
+// CHECK-NEXT:   12019:  e8 16 00 00 00 calll 22
 
 .section .R_386_GOT32,"ax",@progbits
 .global R_386_GOT32
 R_386_GOT32:
         movl zed@GOT, %eax
 // This is the second symbol in the got, so the offset is 4.
 // CHECK:      Disassembly of section .R_386_GOT32:
 // CHECK-NEXT: R_386_GOT32:
 // CHECK-NEXT:   1201e:  {{.*}} movl 4, %eax