[ELF] - R_386_GOT32 relocation calculation fix.

[grimar]

Summary

R_386_GOT32 has multiple descriptions:

1. "System V Application Binary Interface Intel386 Architecture Processor Supplement Version 1.1" (https://github.com/hjl-tools/x86-psABI/wiki/intel386-psABI-1.1.pdf), p36 contains next calculation for R_386_GOT32: G + A - GOT.
2. SYSTEM V APPLICATION BINARY INTERFACE 4 (https://refspecs.linuxfoundation.org/elf/abi386-4.pdf, p78) tolds us its G + A - P.
3. Oracle docs (https://docs.oracle.com/cd/E19455-01/816-0559/chapter6-26/index.html) says its should be G + A.
4. gold/bfd calculates it as (gotentryaddr - gotsize + A), so it is some negative offset.

Patch implements gold/bfs behavior to be consistent with.

[• rafael]

LGTM

ELF/Target.cpp

392 ↗

(On Diff #43537)

In other words, it is "G + A - GOT", but GOT means the end of the GOT section.

[grimar]

In D15750#329381, @rafael wrote:

LGTM

Thanks for review !

lld/trunk/ELF/Target.cpp

 
 void X86TargetInfo::relocateOne(uint8_t *Loc, uint8_t *BufEnd, uint32_t Type,
                                 uint64_t P, uint64_t SA, uint64_t ZA,
                                 uint8_t *PairedLoc) const {
   switch (Type) {
   case R_386_32:
     add32le(Loc, SA);
     break;
-  case R_386_GOT32:
+  case R_386_GOT32: {
+    uint64_t V = SA - Out<ELF32LE>::Got->getVA() -
+                 Out<ELF32LE>::Got->getNumEntries() * 4;
+    checkInt<32>(V, Type);
+    add32le(Loc, V);
+    break;
+  }
   case R_386_GOTOFF:
     add32le(Loc, SA - Out<ELF32LE>::Got->getVA());
     break;
   case R_386_GOTPC:
     add32le(Loc, SA + Out<ELF32LE>::Got->getVA() - P);
     break;
   case R_386_PC32:
   case R_386_PLT32:

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

 movl bar@GOT, %eax
 
 // ADDR:      Name: .plt
 // ADDR-NEXT: Type: SHT_PROGBITS
 // ADDR-NEXT: Flags [
 // ADDR-NEXT:   SHF_ALLOC
 // ADDR-NEXT:   SHF_EXECINSTR
 // ADDR-NEXT: ]
-// ADDR-NEXT: Address: 0x11030
-// ADDR-NEXT: Offset: 0x1030
+// ADDR-NEXT: Address: 0x11040
+// ADDR-NEXT: Offset: 0x1040
 // ADDR-NEXT: Size: 32
 
 // ADDR:      Name: .got
 // ADDR-NEXT: Type: SHT_PROGBITS
 // ADDR-NEXT: Flags [
 // ADDR-NEXT:   SHF_ALLOC
 // ADDR-NEXT:   SHF_WRITE
 // ADDR-NEXT: ]
 // ADDR-NEXT: Address: 0x12078
 
 .section .R_386_GOTPC,"ax",@progbits
 R_386_GOTPC:
  movl $_GLOBAL_OFFSET_TABLE_, %eax
 
 // 0x12050 - 0x11014 = 4156
 
 // CHECK:      Disassembly of section .R_386_GOTPC:
 // CHECK-NEXT: R_386_GOTPC:
 // CHECK-NEXT:   11014:  {{.*}} movl  $4196, %eax
 
 .section .dynamic_reloc, "ax",@progbits
  call bar
-// 0x11030 - (0x11019 + 5) = 18
+// addr(.plt) + 16 - (0x11019 + 5) = 50
 // CHECK:      Disassembly of section .dynamic_reloc:
 // CHECK-NEXT: .dynamic_reloc:
-// CHECK-NEXT:   11019:  e8 22 00 00 00 calll 34
+// CHECK-NEXT:   11019:  e8 32 00 00 00 calll 50
 
 .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.
+ movl bar@GOT, %eax
+ movl bar+8@GOT, %eax
+ movl zed+4@GOT, %eax
+
+// 4294967288 = 0xFFFFFFF8 = got[0](0x12070) - .got(0x12070) - sizeof(.got)(8)
+// 4294967292 = 0xFFFFFFFC = got[1](0x12074) - .got(0x12070) - sizeof(.got)(8)
+// 0xFFFFFFF8 + 8 = 0
+// 0xFFFFFFFC + 4 = 0
 // CHECK:      Disassembly of section .R_386_GOT32:
 // CHECK-NEXT: R_386_GOT32:
-// CHECK-NEXT:   1101e:  {{.*}} movl 4, %eax
+// CHECK-NEXT: 1101e: a1 f8 ff ff ff movl 4294967288, %eax
+// CHECK-NEXT: 11023: a1 fc ff ff ff movl 4294967292, %eax
+// CHECK-NEXT: 11028: a1 00 00 00 00 movl 0, %eax
+// CHECK-NEXT: 1102d: a1 00 00 00 00 movl 0, %eax