[PATCH] D48095: [ELF][X86_64] Use R_GOTREL_FROM_END instead of R_GOTREL for R_X86_64_GOTOFF64

[Fangrui Song via Phabricator via llvm-commits]

MaskRay updated this revision to Diff 151064.
MaskRay added a comment.

.


Repository:
  rLLD LLVM Linker

https://reviews.llvm.org/D48095

Files:
  ELF/Arch/X86_64.cpp
  test/ELF/x86-64-reloc-got.s
  test/ELF/x86-64-reloc-gotoff64.s


Index: test/ELF/x86-64-reloc-gotoff64.s
===================================================================
--- test/ELF/x86-64-reloc-gotoff64.s
+++ /dev/null
@@ -1,17 +0,0 @@
-// 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
-
-// CHECK: .dynamic DYNAMIC  0000000000002000 002000
-// CHECK: .got     PROGBITS 0000000000002070 002070
-
-// DISASM: 1000: 48 ba 90 ff ff ff ff ff ff ff   movabsq $-112, %rdx
-
-.global _start
-.weak _DYNAMIC
-.hidden _DYNAMIC
-_start:
-  movabsq $_DYNAMIC at GOTOFF, %rdx
Index: test/ELF/x86-64-reloc-got.s
===================================================================
--- test/ELF/x86-64-reloc-got.s
+++ test/ELF/x86-64-reloc-got.s
@@ -4,17 +4,34 @@
 // 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
 
-// 0x3070 (.got end) - 0x1007 = 8297
-// CHECK: gotpc32:
-// CHECK-NEXT: 1000: {{.*}} leaq 8297(%rip), %r15
-.global gotpc32
-gotpc32:
-  leaq _GLOBAL_OFFSET_TABLE_(%rip), %r15
+// FIXME: All the _GLOBAL_OFFSET_TABLE_ occurrences below refer to the address
+// of GOT base, not the address of the symbol _GLOBAL_OFFSET_TABLE_, as these
+// instructions are special and they produce GOT base relative relocations. We
+// currently use .got end as the GOT base, which is not equal to
+// _GLOBAL_OFFSET_TABLE_.
 
+// 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
+
+// The assembly is generated by
+// clang++ -S -mcmodel=medium -fPIC a.c
+// extern long _DYNAMIC[] __attribute__((visibility("hidden")));
+// long* dynamic() { return _DYNAMIC; }
+
+// 0x3070 (.got end) - 0x100a = 8287
+// 0x3000 (_DYNAMIC) - 0x3070 (.got end) = -112
+// CHECK:      100a: {{.*}} leaq 8287(%rip), %rdx
+// CHECK-NEXT: 1011: {{.*}} movabsq $-112, %rax
+.global dynamic
+dynamic:
+  leaq _GLOBAL_OFFSET_TABLE_(%rip), %rdx
+  movabsq $_DYNAMIC at GOTOFF, %rax
+  addq %rdx, %rax
+  ret
Index: ELF/Arch/X86_64.cpp
===================================================================
--- ELF/Arch/X86_64.cpp
+++ ELF/Arch/X86_64.cpp
@@ -106,7 +106,7 @@
   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;


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