[ELF][X86_64] Use R_GOTREL_FROM_END instead of R_GOTREL for R_X86_64_GOTOFF64

Summary:
R_X86_64_GOTOFF64: S + A - GOT
R_X86_64_GOTPC{32,64}: GOT + A - P (R_GOTONLY_PC_FROM_END)

R_X86_64_GOTOFF64 should use R_GOTREL_FROM_END so that in conjunction with
R_X86_64_GOTPC{32,64}, the `GOT` term is neutralized. This also matches
the handling of R_386_GOTOFF (S + A - GOT).

Reviewers: ruiu, espindola

Subscribers: emaste, arichardson, llvm-commits

Differential Revision: https://reviews.llvm.org/D48095

llvm-svn: 334672

3 files changed, 30 insertions, 21 deletions

diff --git a/lld/ELF/Arch/X86_64.cpp b/lld/ELF/Arch/X86_64.cpp
index 2a6d22a3015..52771c401b4 100644
--- a/lld/ELF/Arch/X86_64.cpp
+++ b/lld/ELF/Arch/X86_64.cpp
@@ -106,7 +106,7 @@ RelExpr X86_64<ELFT>::getRelExpr(RelType Type, const Symbol &S,
   case R_X86_64_GOTTPOFF:
     return R_GOT_PC;
   case R_X86_64_GOTOFF64:
-    return R_GOTREL;
+    return R_GOTREL_FROM_END;
   case R_X86_64_GOTPC32:
   case R_X86_64_GOTPC64:
     return R_GOTONLY_PC_FROM_END;
diff --git a/lld/test/ELF/x86-64-reloc-gotoff64.s b/lld/test/ELF/x86-64-reloc-gotoff64.s
index 91df28af642..697ac17917a 100644
--- a/lld/test/ELF/x86-64-reloc-gotoff64.s
+++ b/lld/test/ELF/x86-64-reloc-gotoff64.s
@@ -1,17 +1,32 @@
 // REQUIRES: x86
-
 // RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t.o
-// RUN: ld.lld -shared -o %t.so %t.o
-// RUN: llvm-readelf -sections %t.so | FileCheck %s
-// RUN: llvm-objdump -d %t.so | FileCheck -check-prefix=DISASM %s
+// RUN: ld.lld %t.o -shared -o %t.so
+// RUN: llvm-readelf -s %t.so | FileCheck %s -check-prefix=SECTION
+// RUN: llvm-objdump -d %t.so | FileCheck %s
+
+// SECTION: .dynamic DYNAMIC 0000000000003000
+// SECTION: .got PROGBITS 0000000000003070 003070 000000
 
-// CHECK: .dynamic DYNAMIC  0000000000002000 002000
-// CHECK: .got     PROGBITS 0000000000002070 002070
+// All the _GLOBAL_OFFSET_TABLE_ occurrences below refer to the address
+// of GOT base, not the address of the symbol _GLOBAL_OFFSET_TABLE_. These
+// instructions are special and produce GOT base relative relocations. We
+// currently use .got end as the GOT base, which is not equal to
+// the address of the special symbol _GLOBAL_OFFSET_TABLE_.
 
-// DISASM: 1000: 48 ba 90 ff ff ff ff ff ff ff   movabsq $-112, %rdx
+// The assembly is generated by
+// gcc -O2 -S -mcmodel=medium -fPIC a.c
+// This computes the pc-relative address (runtime address) of _DYNAMIC.
+//
+// extern long _DYNAMIC[] __attribute__((visibility("hidden")));
+// long* dynamic() { return _DYNAMIC; }
 
-.global _start
-.weak _DYNAMIC
-.hidden _DYNAMIC
-_start:
-  movabsq $_DYNAMIC@GOTOFF, %rdx
+// 0x3070 (.got end) - 0x1007 = 8297
+// 0x3000 (_DYNAMIC) - 0x3070 (.got end) = -112
+// CHECK:      1000: {{.*}} leaq 8297(%rip), %rdx
+// CHECK-NEXT: 1007: {{.*}} movabsq $-112, %rax
+.global dynamic
+dynamic:
+  leaq _GLOBAL_OFFSET_TABLE_(%rip), %rdx
+  movabsq $_DYNAMIC@GOTOFF, %rax
+  addq %rdx, %rax
+  ret
diff --git a/lld/test/ELF/x86-64-reloc-got.s b/lld/test/ELF/x86-64-reloc-gotpc64.s
index fd95b1feac8..f07376f4121 100644
--- a/lld/test/ELF/x86-64-reloc-got.s
+++ b/lld/test/ELF/x86-64-reloc-gotpc64.s
@@ -6,15 +6,9 @@
 
 // SECTION: .got PROGBITS 0000000000003070 003070 000000
 
-// 0x3070 (.got end) - 0x1007 = 8297
-// CHECK: gotpc32:
-// CHECK-NEXT: 1000: {{.*}} leaq 8297(%rip), %r15
-.global gotpc32
-gotpc32:
-  leaq _GLOBAL_OFFSET_TABLE_(%rip), %r15
-
+// 0x3070 (.got end) - 0x1000 = 8304
 // CHECK: gotpc64:
-// CHECK-NEXT: 1007: {{.*}} movabsq $8297, %r11
+// CHECK-NEXT: 1000: {{.*}} movabsq $8304, %r11
 .global gotpc64
 gotpc64:
   movabsq $_GLOBAL_OFFSET_TABLE_-., %r11