[llvm] [SPARC][IAS] Emit the correct 32-bit ELF machine type (PR #96583)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-sparc

Author: Koakuma (koachan)

<details>
<summary>Changes</summary>

Emit the correct machine type when writing out 32-bit ELF objects. This patch is modeled on GCC's behavior:
- `-m32` emits an object of type EM_SPARC;
- `-m32 -mcpu=v9` emits EM_SPARC32PLUS (however, see below); and
- `-m64` emits EM_SPARCV9.

Note:
GNU as doesn't actually support user control of emitted machine type. It will always autodetect the type based on the instruction mix:
- If there's a V9 instruction inside, then use EM_SPARC32PLUS; and
- Emit EM_SPARC otherwise.

GCC simply happens to try to emit V9 instructions whenever possible with `-m32 -mcpu=v9`, so there's a high chance that the resulting object file will be of a EM_SPARC32PLUS type, however it is not a guaranteed behavior.

For this patch, I opt for deterministic behavior for simplicity.

---
Full diff: https://github.com/llvm/llvm-project/pull/96583.diff


3 Files Affected:

- (modified) llvm/lib/Target/Sparc/MCTargetDesc/SparcAsmBackend.cpp (+11-6) 
- (modified) llvm/lib/Target/Sparc/MCTargetDesc/SparcELFObjectWriter.cpp (+8-6) 
- (modified) llvm/lib/Target/Sparc/MCTargetDesc/SparcMCTargetDesc.h (+2-2) 


``````````diff
diff --git a/llvm/lib/Target/Sparc/MCTargetDesc/SparcAsmBackend.cpp b/llvm/lib/Target/Sparc/MCTargetDesc/SparcAsmBackend.cpp
index cb7414fddd29f..046f81363d294 100644
--- a/llvm/lib/Target/Sparc/MCTargetDesc/SparcAsmBackend.cpp
+++ b/llvm/lib/Target/Sparc/MCTargetDesc/SparcAsmBackend.cpp
@@ -132,14 +132,18 @@ namespace {
   class SparcAsmBackend : public MCAsmBackend {
   protected:
     const Target &TheTarget;
+    const MCSubtargetInfo &TheSTI;
     bool Is64Bit;
+    bool HasV9;
 
   public:
-    SparcAsmBackend(const Target &T)
+    SparcAsmBackend(const Target &T, const MCSubtargetInfo &STI)
         : MCAsmBackend(StringRef(T.getName()) == "sparcel"
                            ? llvm::endianness::little
                            : llvm::endianness::big),
-          TheTarget(T), Is64Bit(StringRef(TheTarget.getName()) == "sparcv9") {}
+          TheTarget(T), TheSTI(STI),
+          Is64Bit(StringRef(TheTarget.getName()) == "sparcv9"),
+          HasV9(TheSTI.hasFeature(Sparc::FeatureV9)) {}
 
     unsigned getNumFixupKinds() const override {
       return Sparc::NumTargetFixupKinds;
@@ -340,8 +344,9 @@ namespace {
   class ELFSparcAsmBackend : public SparcAsmBackend {
     Triple::OSType OSType;
   public:
-    ELFSparcAsmBackend(const Target &T, Triple::OSType OSType) :
-      SparcAsmBackend(T), OSType(OSType) { }
+    ELFSparcAsmBackend(const Target &T, const MCSubtargetInfo &STI,
+                       Triple::OSType OSType)
+        : SparcAsmBackend(T, STI), OSType(OSType) {}
 
     void applyFixup(const MCAssembler &Asm, const MCFixup &Fixup,
                     const MCValue &Target, MutableArrayRef<char> Data,
@@ -368,7 +373,7 @@ namespace {
     std::unique_ptr<MCObjectTargetWriter>
     createObjectTargetWriter() const override {
       uint8_t OSABI = MCELFObjectTargetWriter::getOSABI(OSType);
-      return createSparcELFObjectWriter(Is64Bit, OSABI);
+      return createSparcELFObjectWriter(Is64Bit, HasV9, OSABI);
     }
   };
 
@@ -378,5 +383,5 @@ MCAsmBackend *llvm::createSparcAsmBackend(const Target &T,
                                           const MCSubtargetInfo &STI,
                                           const MCRegisterInfo &MRI,
                                           const MCTargetOptions &Options) {
-  return new ELFSparcAsmBackend(T, STI.getTargetTriple().getOS());
+  return new ELFSparcAsmBackend(T, STI, STI.getTargetTriple().getOS());
 }
diff --git a/llvm/lib/Target/Sparc/MCTargetDesc/SparcELFObjectWriter.cpp b/llvm/lib/Target/Sparc/MCTargetDesc/SparcELFObjectWriter.cpp
index f17d3e997452d..bfd71af736231 100644
--- a/llvm/lib/Target/Sparc/MCTargetDesc/SparcELFObjectWriter.cpp
+++ b/llvm/lib/Target/Sparc/MCTargetDesc/SparcELFObjectWriter.cpp
@@ -21,10 +21,12 @@ using namespace llvm;
 namespace {
   class SparcELFObjectWriter : public MCELFObjectTargetWriter {
   public:
-    SparcELFObjectWriter(bool Is64Bit, uint8_t OSABI)
-      : MCELFObjectTargetWriter(Is64Bit, OSABI,
-                                Is64Bit ?  ELF::EM_SPARCV9 : ELF::EM_SPARC,
-                                /*HasRelocationAddend*/ true) {}
+    SparcELFObjectWriter(bool Is64Bit, bool HasV9, uint8_t OSABI)
+        : MCELFObjectTargetWriter(
+              Is64Bit, OSABI,
+              Is64Bit ? ELF::EM_SPARCV9
+                      : (HasV9 ? ELF::EM_SPARC32PLUS : ELF::EM_SPARC),
+              /*HasRelocationAddend*/ true) {}
 
     ~SparcELFObjectWriter() override = default;
 
@@ -146,6 +148,6 @@ bool SparcELFObjectWriter::needsRelocateWithSymbol(const MCValue &,
 }
 
 std::unique_ptr<MCObjectTargetWriter>
-llvm::createSparcELFObjectWriter(bool Is64Bit, uint8_t OSABI) {
-  return std::make_unique<SparcELFObjectWriter>(Is64Bit, OSABI);
+llvm::createSparcELFObjectWriter(bool Is64Bit, bool HasV9, uint8_t OSABI) {
+  return std::make_unique<SparcELFObjectWriter>(Is64Bit, HasV9, OSABI);
 }
diff --git a/llvm/lib/Target/Sparc/MCTargetDesc/SparcMCTargetDesc.h b/llvm/lib/Target/Sparc/MCTargetDesc/SparcMCTargetDesc.h
index a2a9f7474c3f9..63419663b722c 100644
--- a/llvm/lib/Target/Sparc/MCTargetDesc/SparcMCTargetDesc.h
+++ b/llvm/lib/Target/Sparc/MCTargetDesc/SparcMCTargetDesc.h
@@ -34,8 +34,8 @@ MCCodeEmitter *createSparcMCCodeEmitter(const MCInstrInfo &MCII,
 MCAsmBackend *createSparcAsmBackend(const Target &T, const MCSubtargetInfo &STI,
                                     const MCRegisterInfo &MRI,
                                     const MCTargetOptions &Options);
-std::unique_ptr<MCObjectTargetWriter> createSparcELFObjectWriter(bool Is64Bit,
-                                                                 uint8_t OSABI);
+std::unique_ptr<MCObjectTargetWriter>
+createSparcELFObjectWriter(bool Is64Bit, bool HasV9, uint8_t OSABI);
 
 // Defines symbolic names for Sparc v9 ASI tag names.
 namespace SparcASITag {

``````````

</details>


https://github.com/llvm/llvm-project/pull/96583