[PATCH] D46319: [MC][ARM] Emit R_ARM_BASE_PREL for _GLOBAL_OFFSET_TABLE_ expressions

[Peter Smith via Phabricator via llvm-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rG31c8e1189619: [MC][ARM] Emit R_ARM_BASE_PREL for _GLOBAL_OFFSET_TABLE_ expressions (authored by psmith).
Herald added a subscriber: hiraditya.
Herald added a project: LLVM.

Changed prior to commit:
  https://reviews.llvm.org/D46319?vs=144732&id=257257#toc

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D46319/new/

https://reviews.llvm.org/D46319

Files:
  llvm/lib/Target/ARM/MCTargetDesc/ARMELFObjectWriter.cpp
  llvm/test/MC/ARM/symbol-variants.s


Index: llvm/test/MC/ARM/symbol-variants.s
===================================================================
--- llvm/test/MC/ARM/symbol-variants.s
+++ llvm/test/MC/ARM/symbol-variants.s
@@ -96,8 +96,16 @@
 @CHECK: 70 R_ARM_TLS_LDM32 f28
 @CHECK: 74 R_ARM_TLS_LDM32 f29
 
+@ relative
+.word f30 - (.Lsym+8)
+ at CHECK: 78 R_ARM_REL32 f30
+
+@ _GLOBAL_OFFSET_TABLE_ relative
+.word _GLOBAL_OFFSET_TABLE_ - (.Lsym+8)
+ at CHECK: 7c R_ARM_BASE_PREL _GLOBAL_OFFSET_TABLE_
+
 @ got_prel
-.word	f30(GOT_PREL) + (. - .Lsym)
-	ldr r3, =f31(GOT_PREL)
-@ CHECK: 78 R_ARM_GOT_PREL f30
-@ CHECK: 80 R_ARM_GOT_PREL f31
+.word   f31(GOT_PREL) + (. - .Lsym)
+        ldr r3, =f32(GOT_PREL)
+ at CHECK: 80 R_ARM_GOT_PREL f31
+ at CHECK: 88 R_ARM_GOT_PREL f32
Index: llvm/lib/Target/ARM/MCTargetDesc/ARMELFObjectWriter.cpp
===================================================================
--- llvm/lib/Target/ARM/MCTargetDesc/ARMELFObjectWriter.cpp
+++ llvm/lib/Target/ARM/MCTargetDesc/ARMELFObjectWriter.cpp
@@ -93,8 +93,15 @@
       switch (Modifier) {
       default:
         llvm_unreachable("Unsupported Modifier");
-      case MCSymbolRefExpr::VK_None:
+      case MCSymbolRefExpr::VK_None: {
+        if (const MCSymbolRefExpr *SymRef = Target.getSymA()) {
+          // For GNU AS compatibility expressions such as
+          // _GLOBAL_OFFSET_TABLE_ - label emit a R_ARM_BASE_PREL relocation.
+          if (SymRef->getSymbol().getName() == "_GLOBAL_OFFSET_TABLE_")
+            return ELF::R_ARM_BASE_PREL;
+        }
         return ELF::R_ARM_REL32;
+      }
       case MCSymbolRefExpr::VK_GOTTPOFF:
         return ELF::R_ARM_TLS_IE32;
       case MCSymbolRefExpr::VK_ARM_GOT_PREL:


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