[DebugInfo][ARM] Fix incorrect debug information for RWPI accessed globals

When compiling for the RWPI relocation model the debug information is wrong:

* the debug location is described as { DW_OP_addr Var }
  instead of { DW_OP_constNu Var DW_OP_bregX 0 DW_OP_plus }
* the relocation type is R_ARM_ABS32 instead of R_ARM_SBREL32

Differential Revision: https://reviews.llvm.org/D111404

llvm/include/llvm/Target/TargetLoweringObjectFile.h

@@ -15,6 +15,7 @@
 #define LLVM_TARGET_TARGETLOWERINGOBJECTFILE_H
 
 #include "llvm/MC/MCObjectFileInfo.h"
+#include "llvm/MC/MCRegister.h"
 #include <cstdint>
 
 namespace llvm {
@@ -219,6 +220,14 @@ public:
     return SupportDebugThreadLocalLocation;
   }
 
+  /// Returns the register used as static base in RWPI variants.
+  virtual const MCRegister getStaticBase() const { return MCRegister::NoRegister; }
+
+  /// Get the target specific RWPI relocation.
+  virtual const MCExpr *getIndirectSymViaRWPI(const MCSymbol *Sym) const {
+    return nullptr;
+  }
+
   /// Get the target specific PC relative GOT entry relocation
   virtual const MCExpr *getIndirectSymViaGOTPCRel(const GlobalValue *GV,
                                                   const MCSymbol *Sym,

llvm/lib/CodeGen/AsmPrinter/DwarfCompileUnit.cpp

@@ -262,14 +262,14 @@ void DwarfCompileUnit::addLocationAttribute(
 
     if (Global) {
       const MCSymbol *Sym = Asm->getSymbol(Global);
+      unsigned PointerSize = Asm->getDataLayout().getPointerSize();
+      assert((PointerSize == 4 || PointerSize == 8) &&
+             "Add support for other sizes if necessary");
       if (Global->isThreadLocal()) {
         if (Asm->TM.useEmulatedTLS()) {
           // TODO: add debug info for emulated thread local mode.
         } else {
           // FIXME: Make this work with -gsplit-dwarf.
-          unsigned PointerSize = Asm->getDataLayout().getPointerSize();
-          assert((PointerSize == 4 || PointerSize == 8) &&
-                 "Add support for other sizes if necessary");
           // Based on GCC's support for TLS:
           if (!DD->useSplitDwarf()) {
             // 1) Start with a constNu of the appropriate pointer size
@@ -292,6 +292,24 @@ void DwarfCompileUnit::addLocationAttribute(
                   DD->useGNUTLSOpcode() ? dwarf::DW_OP_GNU_push_tls_address
                                         : dwarf::DW_OP_form_tls_address);
         }
+      } else if (Asm->TM.getRelocationModel() == Reloc::RWPI ||
+                 Asm->TM.getRelocationModel() == Reloc::ROPI_RWPI) {
+        // Constant
+        addUInt(*Loc, dwarf::DW_FORM_data1,
+                PointerSize == 4 ? dwarf::DW_OP_const4u
+                                 : dwarf::DW_OP_const8u);
+        // Relocation offset
+        addExpr(*Loc, PointerSize == 4 ? dwarf::DW_FORM_data4
+                                       : dwarf::DW_FORM_data8,
+                Asm->getObjFileLowering().getIndirectSymViaRWPI(Sym));
+        // Base register
+        Register BaseReg = Asm->getObjFileLowering().getStaticBase();
+        BaseReg = Asm->TM.getMCRegisterInfo()->getDwarfRegNum(BaseReg, false);
+        addUInt(*Loc, dwarf::DW_FORM_data1, dwarf::DW_OP_breg0 + BaseReg);
+        // Offset from base register
+        addSInt(*Loc, dwarf::DW_FORM_sdata, 0);
+        // Operation
+        addUInt(*Loc, dwarf::DW_FORM_data1, dwarf::DW_OP_plus);
       } else {
         DD->addArangeLabel(SymbolCU(this, Sym));
         addOpAddress(*Loc, Sym);

llvm/lib/Target/ARM/ARMTargetObjectFile.cpp

@@ -54,6 +54,16 @@ void ARMElfTargetObjectFile::Initialize(MCContext &Ctx,
   }
 }
 
+const MCRegister ARMElfTargetObjectFile::getStaticBase() const {
+  return ARM::R9;
+}
+
+const MCExpr *ARMElfTargetObjectFile::
+getIndirectSymViaRWPI(const MCSymbol *Sym) const {
+  return MCSymbolRefExpr::create(Sym, MCSymbolRefExpr::VK_ARM_SBREL,
+                                 getContext());
+}
+
 const MCExpr *ARMElfTargetObjectFile::getTTypeGlobalReference(
     const GlobalValue *GV, unsigned Encoding, const TargetMachine &TM,
     MachineModuleInfo *MMI, MCStreamer &Streamer) const {

llvm/lib/Target/ARM/ARMTargetObjectFile.h

@@ -11,6 +11,7 @@
 
 #include "llvm/CodeGen/TargetLoweringObjectFileImpl.h"
 #include "llvm/MC/MCExpr.h"
+#include "llvm/MC/MCRegister.h"
 
 namespace llvm {
 
@@ -23,6 +24,10 @@ public:
 
   void Initialize(MCContext &Ctx, const TargetMachine &TM) override;
 
+  const MCRegister getStaticBase() const override;
+
+  const MCExpr *getIndirectSymViaRWPI(const MCSymbol *Sym) const override;
+
   const MCExpr *getTTypeGlobalReference(const GlobalValue *GV,
                                         unsigned Encoding,
                                         const TargetMachine &TM,

llvm/test/DebugInfo/ARM/rwpi.ll

@@ -0,0 +1,34 @@
+; RUN: llc -mtriple armv7-linux -relocation-model=rwpi -o - %s | FileCheck %s
+; RUN: llc -mtriple armv7-linux -relocation-model=ropi-rwpi -o - %s | FileCheck %s
+
+@global = global i32 5, align 4, !dbg !0
+
+; 8 bytes of data
+; CHECK:      .byte 8 @ DW_AT_location
+; DW_OP_const4u
+; CHECK-NEXT: .byte 12
+; relocation offset
+; CHECK-NEXT: .long global(sbrel)
+; DW_OP_breg9
+; CHECK-NEXT: .byte 121
+; offset from breg9
+; CHECK-NEXT: .byte 0
+; DW_OP_plus
+; CHECK-NEXT: .byte 34
+
+!llvm.dbg.cu = !{!2}
+!llvm.module.flags = !{!6, !7, !8, !9, !10}
+!llvm.ident = !{!11}
+
+!0 = !DIGlobalVariableExpression(var: !1, expr: !DIExpression())
+!1 = distinct !DIGlobalVariable(name: "global", scope: !2, file: !3, line: 1, type: !5, isLocal: false, isDefinition: true)
+!2 = distinct !DICompileUnit(language: DW_LANG_C99, file: !3, producer: "clang version 14.0.0 (https://github.com/llvm/llvm-project.git 9f5c70c7ad404f0cb52416a0574d9e48d520be5d)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, globals: !4, splitDebugInlining: false, nameTableKind: None)
+!3 = !DIFile(filename: "rwpi.c", directory: "/tmp")
+!4 = !{!0}
+!5 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!6 = !{i32 7, !"Dwarf Version", i32 4}
+!7 = !{i32 2, !"Debug Info Version", i32 3}
+!8 = !{i32 1, !"wchar_size", i32 4}
+!9 = !{i32 1, !"min_enum_size", i32 4}
+!10 = !{i32 7, !"frame-pointer", i32 2}
+!11 = !{!"clang version 14.0.0 (https://github.com/llvm/llvm-project.git 9f5c70c7ad404f0cb52416a0574d9e48d520be5d)"}