[llvm] 322799a - [llvm] Support indirect symbol replacement with GOTPCREL for x86_64 ELF (#67754)

[via llvm-commits]

Author: PiJoules
Date: 2023-11-15T15:13:31-08:00
New Revision: 322799aa5010812550eec6b300bce185b6718109

URL: https://github.com/llvm/llvm-project/commit/322799aa5010812550eec6b300bce185b6718109
DIFF: https://github.com/llvm/llvm-project/commit/322799aa5010812550eec6b300bce185b6718109.diff

LOG: [llvm] Support indirect symbol replacement with GOTPCREL for x86_64 ELF (#67754)

There's an existing check in LLVM that can replace an offset to a
DSO-local symbol that is just a pointer to another symbol with a
GOTPCREL reloc. This is exactly what the RTTI proxy in the relative
vtables ABI is. This feature is supported for different macho platforms,
but not for ELF. This extends that support.

Added: 
    llvm/test/MC/ELF/rtti-proxy-gotpcrel.ll

Modified: 
    llvm/lib/Target/X86/X86TargetObjectFile.cpp
    llvm/lib/Target/X86/X86TargetObjectFile.h

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Target/X86/X86TargetObjectFile.cpp b/llvm/lib/Target/X86/X86TargetObjectFile.cpp
index b88ad5a478f390a..53c692060f08cf1 100644
--- a/llvm/lib/Target/X86/X86TargetObjectFile.cpp
+++ b/llvm/lib/Target/X86/X86TargetObjectFile.cpp
@@ -56,3 +56,13 @@ const MCExpr *X86ELFTargetObjectFile::getDebugThreadLocalSymbol(
     const MCSymbol *Sym) const {
   return MCSymbolRefExpr::create(Sym, MCSymbolRefExpr::VK_DTPOFF, getContext());
 }
+
+const MCExpr *X86ELFTargetObjectFile::getIndirectSymViaGOTPCRel(
+    const GlobalValue *GV, const MCSymbol *Sym, const MCValue &MV,
+    int64_t Offset, MachineModuleInfo *MMI, MCStreamer &Streamer) const {
+  int64_t FinalOffset = Offset + MV.getConstant();
+  const MCExpr *Res =
+      MCSymbolRefExpr::create(Sym, MCSymbolRefExpr::VK_GOTPCREL, getContext());
+  const MCExpr *Off = MCConstantExpr::create(FinalOffset, getContext());
+  return MCBinaryExpr::createAdd(Res, Off, getContext());
+}

diff  --git a/llvm/lib/Target/X86/X86TargetObjectFile.h b/llvm/lib/Target/X86/X86TargetObjectFile.h
index f4bf52c83771ff4..ed9390d1fad1a26 100644
--- a/llvm/lib/Target/X86/X86TargetObjectFile.h
+++ b/llvm/lib/Target/X86/X86TargetObjectFile.h
@@ -42,9 +42,16 @@ namespace llvm {
   public:
     X86ELFTargetObjectFile() {
       PLTRelativeVariantKind = MCSymbolRefExpr::VK_PLT;
+      SupportIndirectSymViaGOTPCRel = true;
     }
     /// Describe a TLS variable address within debug info.
     const MCExpr *getDebugThreadLocalSymbol(const MCSymbol *Sym) const override;
+
+    const MCExpr *
+    getIndirectSymViaGOTPCRel(const GlobalValue *GV, const MCSymbol *Sym,
+                              const MCValue &MV, int64_t Offset,
+                              MachineModuleInfo *MMI,
+                              MCStreamer &Streamer) const override;
   };
 
 } // end namespace llvm

diff  --git a/llvm/test/MC/ELF/rtti-proxy-gotpcrel.ll b/llvm/test/MC/ELF/rtti-proxy-gotpcrel.ll
new file mode 100644
index 000000000000000..c58bb5b77c6c5dd
--- /dev/null
+++ b/llvm/test/MC/ELF/rtti-proxy-gotpcrel.ll
@@ -0,0 +1,27 @@
+; RUN: llc %s -mtriple=x86_64-unknown-fuchsia  -o - | FileCheck %s
+
+ at vtable = dso_local unnamed_addr constant i32 trunc (i64 sub (i64 ptrtoint (ptr @rtti.proxy to i64), i64 ptrtoint (ptr @vtable to i64)) to i32), align 4
+ at vtable_with_offset = dso_local unnamed_addr constant [2 x i32] [i32 0, i32 trunc (i64 sub (i64 ptrtoint (ptr @rtti.proxy to i64), i64 ptrtoint (ptr @vtable_with_offset to i64)) to i32)], align 4
+ at vtable_with_negative_offset = dso_local unnamed_addr constant [2 x i32] [
+  i32 trunc (
+    i64 sub (
+      i64 ptrtoint (ptr @rtti.proxy to i64),
+      i64 ptrtoint (ptr getelementptr inbounds ([2 x i32], ptr @vtable_with_negative_offset, i32 0, i32 1) to i64)
+    )
+    to i32),
+  i32 0
+], align 4
+ at rtti = external global i8, align 8
+ at rtti.proxy = linkonce_odr hidden unnamed_addr constant ptr @rtti
+
+; CHECK-NOT: rtti.proxy
+; CHECK-LABEL: vtable:
+; CHECK-NEXT:    .{{word|long}}   rtti at GOTPCREL+0{{$}}
+
+; CHECK-LABEL: vtable_with_offset:
+; CHECK-NEXT:    .{{word|long}}   0
+; CHECK-NEXT:    .{{word|long}}   rtti at GOTPCREL+4{{$}}
+
+; CHECK-LABEL: vtable_with_negative_offset:
+; CHECK-NEXT:    .{{word|long}}   rtti at GOTPCREL-4{{$}}
+; CHECK-NEXT:    .{{word|long}}   0