[PowerPC] Add assembly directives to change endianness

[DanilaZhebryakov]

Add simple assembly directives to change endianness of the code being assembled. This is useful in some edge cases to write code involving different endian modes.
Relocations in 'non-native' endian don't work.

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[llvmbot]

@llvm/pr-subscribers-mc

@llvm/pr-subscribers-backend-powerpc

Author: None (DanilaZhebryakov)

Changes

Add simple assembly directives to change endianness of the code being assembled. This is useful in some edge cases to write code involving different endian modes.
Relocations in 'non-native' endian don't work.

---

Full diff: https://github.com/llvm/llvm-project/pull/149811.diff

5 Files Affected:

• (modified) llvm/lib/Target/PowerPC/AsmParser/PPCAsmParser.cpp (+11-1)
• (modified) llvm/lib/Target/PowerPC/MCTargetDesc/PPCMCCodeEmitter.h (+2)
• (modified) llvm/lib/Target/PowerPC/MCTargetDesc/PPCMCTargetDesc.cpp (+22)
• (modified) llvm/lib/Target/PowerPC/MCTargetDesc/PPCTargetStreamer.h (+1)
• (added) llvm/test/MC/PowerPC/endian-directive.s (+10)

diff --git a/llvm/lib/Target/PowerPC/AsmParser/PPCAsmParser.cpp b/llvm/lib/Target/PowerPC/AsmParser/PPCAsmParser.cpp
index 58766b16e86fe..17877954758be 100644
--- a/llvm/lib/Target/PowerPC/AsmParser/PPCAsmParser.cpp
+++ b/llvm/lib/Target/PowerPC/AsmParser/PPCAsmParser.cpp
@@ -1655,7 +1655,17 @@ bool PPCAsmParser::ParseDirective(AsmToken DirectiveID) {
     parseDirectiveTC(isPPC64() ? 8 : 4, DirectiveID);
   else if (IDVal == ".machine")
     parseDirectiveMachine(DirectiveID.getLoc());
-  else if (IDVal == ".abiversion")
+  else if (IDVal == ".big") {
+    PPCTargetStreamer *TStreamer = static_cast<PPCTargetStreamer *>(
+        getParser().getStreamer().getTargetStreamer());
+    if (TStreamer != nullptr)
+      TStreamer->emitEndianSet(false);
+  } else if (IDVal == ".little") {
+    PPCTargetStreamer *TStreamer = static_cast<PPCTargetStreamer *>(
+        getParser().getStreamer().getTargetStreamer());
+    if (TStreamer != nullptr)
+      TStreamer->emitEndianSet(true);
+  } else if (IDVal == ".abiversion")
     parseDirectiveAbiVersion(DirectiveID.getLoc());
   else if (IDVal == ".localentry")
     parseDirectiveLocalEntry(DirectiveID.getLoc());
diff --git a/llvm/lib/Target/PowerPC/MCTargetDesc/PPCMCCodeEmitter.h b/llvm/lib/Target/PowerPC/MCTargetDesc/PPCMCCodeEmitter.h
index b574557183194..a24b061eead8c 100644
--- a/llvm/lib/Target/PowerPC/MCTargetDesc/PPCMCCodeEmitter.h
+++ b/llvm/lib/Target/PowerPC/MCTargetDesc/PPCMCCodeEmitter.h
@@ -125,6 +125,8 @@ class PPCMCCodeEmitter : public MCCodeEmitter {
   /// Check if Opcode corresponds to a call instruction that should be marked
   /// with the NOTOC relocation.
   bool isNoTOCCallInstr(const MCInst &MI) const;
+
+  void setLittleEndian(bool little_endian) { IsLittleEndian = little_endian; }
 };
 
 } // namespace llvm
diff --git a/llvm/lib/Target/PowerPC/MCTargetDesc/PPCMCTargetDesc.cpp b/llvm/lib/Target/PowerPC/MCTargetDesc/PPCMCTargetDesc.cpp
index 54497d9c2fedf..68cc96c58e122 100644
--- a/llvm/lib/Target/PowerPC/MCTargetDesc/PPCMCTargetDesc.cpp
+++ b/llvm/lib/Target/PowerPC/MCTargetDesc/PPCMCTargetDesc.cpp
@@ -15,6 +15,7 @@
 #include "MCTargetDesc/PPCMCAsmInfo.h"
 #include "PPCELFStreamer.h"
 #include "PPCMCAsmInfo.h"
+#include "PPCMCCodeEmitter.h"
 #include "PPCTargetStreamer.h"
 #include "PPCXCOFFStreamer.h"
 #include "TargetInfo/PowerPCTargetInfo.h"
@@ -246,6 +247,10 @@ class PPCTargetAsmStreamer : public PPCTargetStreamer {
       OS << "\t.machine " << CPU << '\n';
   }
 
+  void emitEndianSet(bool little) override {
+    OS << (little ? "\t.little\n" : "\t.big\n");
+  }
+
   void emitAbiVersion(int AbiVersion) override {
     OS << "\t.abiversion " << AbiVersion << '\n';
   }
@@ -280,6 +285,13 @@ class PPCTargetELFStreamer : public PPCTargetStreamer {
     // limit the parser?
   }
 
+  void emitEndianSet(bool little) override {
+    PPCMCCodeEmitter *emitter = static_cast<PPCMCCodeEmitter *>(
+        getStreamer().getAssembler().getEmitterPtr());
+    if (emitter != nullptr)
+      emitter->setLittleEndian(little);
+  }
+
   void emitAbiVersion(int AbiVersion) override {
     ELFObjectWriter &W = getStreamer().getWriter();
     unsigned Flags = W.getELFHeaderEFlags();
@@ -408,6 +420,16 @@ class PPCTargetXCOFFStreamer : public PPCTargetStreamer {
         .setCPU(CPU);
   }
 
+  void emitEndianSet(bool little) override {
+    MCAssembler *assembler = getStreamer().getAssemblerPtr();
+    if (assembler == nullptr)
+      return;
+    PPCMCCodeEmitter *emitter =
+        static_cast<PPCMCCodeEmitter *>(assembler->getEmitterPtr());
+    if (emitter != nullptr)
+      emitter->setLittleEndian(little);
+  }
+
   void emitAbiVersion(int AbiVersion) override {
     llvm_unreachable("ABI-version pseudo-ops are invalid for XCOFF.");
   }
diff --git a/llvm/lib/Target/PowerPC/MCTargetDesc/PPCTargetStreamer.h b/llvm/lib/Target/PowerPC/MCTargetDesc/PPCTargetStreamer.h
index 3da034d4909ff..9c8d50a300a2a 100644
--- a/llvm/lib/Target/PowerPC/MCTargetDesc/PPCTargetStreamer.h
+++ b/llvm/lib/Target/PowerPC/MCTargetDesc/PPCTargetStreamer.h
@@ -27,6 +27,7 @@ class PPCTargetStreamer : public MCTargetStreamer {
 
   virtual void emitTCEntry(const MCSymbol &S, PPCMCExpr::Specifier Kind) {}
   virtual void emitMachine(StringRef CPU){};
+  virtual void emitEndianSet(bool little) {};
   virtual void emitAbiVersion(int AbiVersion){};
   virtual void emitLocalEntry(MCSymbolELF *S, const MCExpr *LocalOffset){};
 };
diff --git a/llvm/test/MC/PowerPC/endian-directive.s b/llvm/test/MC/PowerPC/endian-directive.s
new file mode 100644
index 0000000000000..69e225135f662
--- /dev/null
+++ b/llvm/test/MC/PowerPC/endian-directive.s
@@ -0,0 +1,10 @@
+# RUN: llvm-mc -filetype=obj -triple=powerpc-unknown-linux-gnu %s | llvm-readobj -x .text - | FileCheck -check-prefix=CHECK-BE %s
+# RUN: llvm-mc -filetype=obj -triple=ppc32le-unknown-linux-gnu %s | llvm-readobj -x .text - | FileCheck -check-prefix=CHECK-LE %s
+add %r0, %r1, %r2
+.big
+add %r0, %r1, %r2
+.little
+add %r0, %r1, %r2
+
+# CHECK-BE: 0x00000000 7c011214 7c011214 1412017c          |...|......|
+# CHECK-LE: 0x00000000 1412017c 7c011214 1412017c          ...||......|