[mips] Switch to the `.text` section after emitting asm file preamble

[atanasyan]

Summary

Now the last .section directive in the MIPS asm file preamble is the .section .mdebug.abi. If assembler code injected for example by the LLVM module asm or the C __asm directives do not contain explicit switching to the .text section it goes to the .mdebug.abi section. It might be unexpected to the user and in fact for example breaks building some existing code like FreeBSD libc [1].

The patch forces switching to the .text section after emitting MIPS assembler file preamble.

[1] https://bugs.llvm.org/show_bug.cgi?id=43119

Fix PR43119.

[Petar.Avramovic]

LGTM.

llvm/lib/Target/Mips/MipsAsmPrinter.cpp

 #include "llvm/MC/MCObjectFileInfo.h"
 #include "llvm/MC/MCSectionELF.h"
 #include "llvm/MC/MCSymbol.h"
 #include "llvm/MC/MCSymbolELF.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/TargetRegistry.h"
 #include "llvm/Support/raw_ostream.h"
+#include "llvm/Target/TargetLoweringObjectFile.h"
 #include "llvm/Target/TargetMachine.h"
 #include <cassert>
 #include <cstdint>
 #include <map>
 #include <memory>
 #include <string>
 #include <vector>
 
if ((ABI.IsO32() && (STI.isABI_FPXX() || STI.isFP64bit())) ||
       STI.useSoftFloat())
     TS.emitDirectiveModuleFP();
 
   // We should always emit a '.module [no]oddspreg' but binutils 2.24 does not
   // accept it. We therefore emit it when it contradicts the default or an
   // option has changed the default (i.e. FPXX) and omit it otherwise.
   if (ABI.IsO32() && (!STI.useOddSPReg() || STI.isABI_FPXX()))
     TS.emitDirectiveModuleOddSPReg();
+
+  // Switch to the .text section.
+  OutStreamer->SwitchSection(getObjFileLowering().getTextSection());
 }
 
 void MipsAsmPrinter::emitInlineAsmStart() const {
   MipsTargetStreamer &TS = getTargetStreamer();
 
   // GCC's choice of assembler options for inline assembly code ('at', 'macro'
   // and 'reorder') is different from LLVM's choice for generated code ('noat',
   // 'nomacro' and 'noreorder').

llvm/test/CodeGen/Mips/start-asm-file.ll

 ; STATIC-N64-NOT: .abicalls
 ; STATIC-N64-NOT: .option pic0
 
 ; PIC-N64: .abicalls
 ; PIC-N64-NOT: .option pic0
 
 ; CHECK: .section .mdebug.abi[[ABI]]
 ; CHECK: .nan [[NAN]]
+; CHECK: .text
 ; CHECK: .file