[X86] Support .reloc *, R_{386,X86_64}_NONE, *

This can be used to create references among sections. When --gc-sections
is used, the referenced section will be retained if the origin section
is retained.

See R_MIPS_NONE (D13659), R_ARM_NONE (D61992), R_AARCH64_NONE (D61973) for similar changes.

Reviewed By: rnk

Differential Revision: https://reviews.llvm.org/D62014

llvm-svn: 360983

4 files changed, 108 insertions, 9 deletions

diff --git a/llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp b/llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp
index 7203f717336..54413fa1a02 100644
--- a/llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp
+++ b/llvm/lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp
@@ -26,18 +26,20 @@
 #include "llvm/Support/raw_ostream.h"
 using namespace llvm;
 
-static unsigned getFixupKindLog2Size(unsigned Kind) {
+static unsigned getFixupKindSize(unsigned Kind) {
   switch (Kind) {
   default:
     llvm_unreachable("invalid fixup kind!");
+  case FK_NONE:
+    return 0;
   case FK_PCRel_1:
   case FK_SecRel_1:
   case FK_Data_1:
-    return 0;
+    return 1;
   case FK_PCRel_2:
   case FK_SecRel_2:
   case FK_Data_2:
-    return 1;
+    return 2;
   case FK_PCRel_4:
   case X86::reloc_riprel_4byte:
   case X86::reloc_riprel_4byte_relax:
@@ -49,12 +51,12 @@ static unsigned getFixupKindLog2Size(unsigned Kind) {
   case X86::reloc_branch_4byte_pcrel:
   case FK_SecRel_4:
   case FK_Data_4:
-    return 2;
+    return 4;
   case FK_PCRel_8:
   case FK_SecRel_8:
   case FK_Data_8:
   case X86::reloc_global_offset_table8:
-    return 3;
+    return 8;
   }
 }
 
@@ -77,6 +79,8 @@ public:
     return X86::NumTargetFixupKinds;
   }
 
+  Optional<MCFixupKind> getFixupKind(StringRef Name) const override;
+
   const MCFixupKindInfo &getFixupKindInfo(MCFixupKind Kind) const override {
     const static MCFixupKindInfo Infos[X86::NumTargetFixupKinds] = {
         {"reloc_riprel_4byte", 0, 32, MCFixupKindInfo::FKF_IsPCRel},
@@ -99,11 +103,14 @@ public:
     return Infos[Kind - FirstTargetFixupKind];
   }
 
+  bool shouldForceRelocation(const MCAssembler &Asm, const MCFixup &Fixup,
+                             const MCValue &Target) override;
+
   void applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
                   const MCValue &Target, MutableArrayRef<char> Data,
                   uint64_t Value, bool IsResolved,
                   const MCSubtargetInfo *STI) const override {
-    unsigned Size = 1 << getFixupKindLog2Size(Fixup.getKind());
+    unsigned Size = getFixupKindSize(Fixup.getKind());
 
     assert(Fixup.getOffset() + Size <= Data.size() && "Invalid fixup offset!");
 
@@ -111,7 +118,7 @@ public:
     // Specifically ignore overflow/underflow as long as the leakage is
     // limited to the lower bits. This is to remain compatible with
     // other assemblers.
-    assert(isIntN(Size * 8 + 1, Value) &&
+    assert((Size == 0 || isIntN(Size * 8 + 1, Value)) &&
            "Value does not fit in the Fixup field");
 
     for (unsigned i = 0; i != Size; ++i)
@@ -236,6 +243,25 @@ static unsigned getRelaxedOpcode(const MCInst &Inst, bool is16BitMode) {
   return getRelaxedOpcodeBranch(Inst, is16BitMode);
 }
 
+Optional<MCFixupKind> X86AsmBackend::getFixupKind(StringRef Name) const {
+  if (STI.getTargetTriple().isOSBinFormatELF()) {
+    if (STI.getTargetTriple().getArch() == Triple::x86_64) {
+      if (Name == "R_X86_64_NONE")
+        return FK_NONE;
+    } else {
+      if (Name == "R_386_NONE")
+        return FK_NONE;
+    }
+  }
+  return MCAsmBackend::getFixupKind(Name);
+}
+
+bool X86AsmBackend::shouldForceRelocation(const MCAssembler &,
+                                          const MCFixup &Fixup,
+                                          const MCValue &) {
+  return Fixup.getKind() == FK_NONE;
+}
+
 bool X86AsmBackend::mayNeedRelaxation(const MCInst &Inst,
                                       const MCSubtargetInfo &STI) const {
   // Branches can always be relaxed in either mode.
diff --git a/llvm/lib/Target/X86/MCTargetDesc/X86ELFObjectWriter.cpp b/llvm/lib/Target/X86/MCTargetDesc/X86ELFObjectWriter.cpp
index 8b6262ec22f..e6939839d28 100644
--- a/llvm/lib/Target/X86/MCTargetDesc/X86ELFObjectWriter.cpp
+++ b/llvm/lib/Target/X86/MCTargetDesc/X86ELFObjectWriter.cpp
@@ -44,7 +44,7 @@ X86ELFObjectWriter::X86ELFObjectWriter(bool IsELF64, uint8_t OSABI,
                               (EMachine != ELF::EM_386) &&
                                   (EMachine != ELF::EM_IAMCU)) {}
 
-enum X86_64RelType { RT64_64, RT64_32, RT64_32S, RT64_16, RT64_8 };
+enum X86_64RelType { RT64_NONE, RT64_64, RT64_32, RT64_32S, RT64_16, RT64_8 };
 
 static X86_64RelType getType64(unsigned Kind,
                                MCSymbolRefExpr::VariantKind &Modifier,
@@ -52,6 +52,8 @@ static X86_64RelType getType64(unsigned Kind,
   switch (Kind) {
   default:
     llvm_unreachable("Unimplemented");
+  case FK_NONE:
+    return RT64_NONE;
   case X86::reloc_global_offset_table8:
     Modifier = MCSymbolRefExpr::VK_GOT;
     IsPCRel = true;
@@ -102,6 +104,10 @@ static unsigned getRelocType64(MCContext &Ctx, SMLoc Loc,
   case MCSymbolRefExpr::VK_None:
   case MCSymbolRefExpr::VK_X86_ABS8:
     switch (Type) {
+    case RT64_NONE:
+      if (Modifier == MCSymbolRefExpr::VK_None)
+        return ELF::R_X86_64_NONE;
+      llvm_unreachable("Unimplemented");
     case RT64_64:
       return IsPCRel ? ELF::R_X86_64_PC64 : ELF::R_X86_64_64;
     case RT64_32:
@@ -123,6 +129,7 @@ static unsigned getRelocType64(MCContext &Ctx, SMLoc Loc,
     case RT64_32S:
     case RT64_16:
     case RT64_8:
+    case RT64_NONE:
       llvm_unreachable("Unimplemented");
     }
     llvm_unreachable("unexpected relocation type!");
@@ -140,6 +147,7 @@ static unsigned getRelocType64(MCContext &Ctx, SMLoc Loc,
     case RT64_32S:
     case RT64_16:
     case RT64_8:
+    case RT64_NONE:
       llvm_unreachable("Unimplemented");
     }
     llvm_unreachable("unexpected relocation type!");
@@ -153,6 +161,7 @@ static unsigned getRelocType64(MCContext &Ctx, SMLoc Loc,
     case RT64_32S:
     case RT64_16:
     case RT64_8:
+    case RT64_NONE:
       llvm_unreachable("Unimplemented");
     }
     llvm_unreachable("unexpected relocation type!");
@@ -166,6 +175,7 @@ static unsigned getRelocType64(MCContext &Ctx, SMLoc Loc,
     case RT64_32S:
     case RT64_16:
     case RT64_8:
+    case RT64_NONE:
       llvm_unreachable("Unimplemented");
     }
     llvm_unreachable("unexpected relocation type!");
@@ -205,10 +215,12 @@ static unsigned getRelocType64(MCContext &Ctx, SMLoc Loc,
   }
 }
 
-enum X86_32RelType { RT32_32, RT32_16, RT32_8 };
+enum X86_32RelType { RT32_NONE, RT32_32, RT32_16, RT32_8 };
 
 static X86_32RelType getType32(X86_64RelType T) {
   switch (T) {
+  case RT64_NONE:
+    return RT32_NONE;
   case RT64_64:
     llvm_unreachable("Unimplemented");
   case RT64_32:
@@ -232,6 +244,10 @@ static unsigned getRelocType32(MCContext &Ctx,
   case MCSymbolRefExpr::VK_None:
   case MCSymbolRefExpr::VK_X86_ABS8:
     switch (Type) {
+    case RT32_NONE:
+      if (Modifier == MCSymbolRefExpr::VK_None)
+        return ELF::R_386_NONE;
+      llvm_unreachable("Unimplemented");
     case RT32_32:
       return IsPCRel ? ELF::R_386_PC32 : ELF::R_386_32;
     case RT32_16:
diff --git a/llvm/test/MC/X86/reloc-directive-elf-32.s b/llvm/test/MC/X86/reloc-directive-elf-32.s
new file mode 100644
index 00000000000..f6e321c94e0
--- /dev/null
+++ b/llvm/test/MC/X86/reloc-directive-elf-32.s
@@ -0,0 +1,31 @@
+# RUN: llvm-mc -triple=i386-pc-linux-musl %s | FileCheck --check-prefix=PRINT %s
+
+# RUN: llvm-mc -filetype=obj -triple=i386-pc-linux-musl %s -o %t
+# RUN: llvm-readobj -r %t | FileCheck %s
+# RUN: llvm-readelf -x .data %t | FileCheck --check-prefix=HEX %s
+
+# PRINT:      .reloc 2, R_386_NONE, .data
+# PRINT-NEXT: .reloc 1, R_386_NONE, foo+4
+# PRINT-NEXT: .reloc 0, R_386_NONE, 8
+
+# X86 relocations use the Elf32_Rel format. Addends are neither stored in the
+# relocation entries nor applied in the referenced locations.
+# CHECK:      0x2 R_386_NONE .data 0x0
+# CHECK-NEXT: 0x1 R_386_NONE foo 0x0
+# CHECK-NEXT: 0x0 R_386_NONE - 0x0
+
+# HEX: 0x00000000 00000000 00000000
+
+.text
+  ret
+  nop
+  nop
+  .reloc 2, R_386_NONE, .data
+  .reloc 1, R_386_NONE, foo+4
+  .reloc 0, R_386_NONE, 8
+
+.data
+.globl foo
+foo:
+  .long 0
+  .long 0
diff --git a/llvm/test/MC/X86/reloc-directive-elf-64.s b/llvm/test/MC/X86/reloc-directive-elf-64.s
new file mode 100644
index 00000000000..e9523d72949
--- /dev/null
+++ b/llvm/test/MC/X86/reloc-directive-elf-64.s
@@ -0,0 +1,26 @@
+# RUN: llvm-mc -triple=x86_64-pc-linux-musl %s | FileCheck --check-prefix=PRINT %s
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux-musl %s -o %t
+# RUN: llvm-readobj -r %t | FileCheck %s
+
+# PRINT:      .reloc 2, R_X86_64_NONE, .data
+# PRINT-NEXT: .reloc 1, R_X86_64_NONE, foo+4
+# PRINT-NEXT: .reloc 0, R_X86_64_NONE, 8
+
+# CHECK:      0x2 R_X86_64_NONE .data 0x0
+# CHECK-NEXT: 0x1 R_X86_64_NONE foo 0x4
+# CHECK-NEXT: 0x0 R_X86_64_NONE - 0x8
+
+.text
+  ret
+  nop
+  nop
+  .reloc 2, R_X86_64_NONE, .data
+  .reloc 1, R_X86_64_NONE, foo+4
+  .reloc 0, R_X86_64_NONE, 8
+
+.data
+.globl foo
+foo:
+  .word 0
+  .word 0