[PowerPC] Fix the EH_SjLj_Setup pseudo.

[• koriakin]

Summary

This instruction is just a control flow marker - it should not
actually exist in the object file. Unfortunately, nothing catches
it before it gets to AsmPrinter. If integrated assembler is used,
it's considered to be a normal 4-byte instruction, and emitted as
an all-0 word, crashing the program. With external assembler,
a comment is emitted.

Fixed by setting Size to 0 and handling it in MCCodeEmitter - this
means the comment will still be emitted if integrated assembler
is not used.

This broke an ASan test, which has been disabled for a long time
as a result (see the discussion on D19657). We can reenable it
once this lands.

[hfinkel]

Can you construct a test case by running llc with -filetype=obj, and then llvm-objdump (or llvm-mc --disassemble or whatever works)?

lib/Target/PowerPC/PPCInstrInfo.td

1406

Please add a comment explaining that this pseudo instruction is never removed from the function because it serves as a terminator, and we set size to 0 to prevent the builtin assembler from emitting it.

[• koriakin]

Added comment and test.

[hfinkel]

LGTM.

[• koriakin]

Closed by rL267943 (forgot to add phab link).

lib/Target/PowerPC/MCTargetDesc/PPCMCCodeEmitter.cpp

void encodeInstruction(const MCInst &MI, raw_ostream &OS,
     unsigned Opcode = MI.getOpcode();
     const MCInstrDesc &Desc = MCII.get(Opcode);
 
     uint64_t Bits = getBinaryCodeForInstr(MI, Fixups, STI);
 
     // Output the constant in big/little endian byte order.
     unsigned Size = Desc.getSize();
     switch (Size) {
+    case 0:
+      break;
     case 4:
       if (IsLittleEndian) {
         support::endian::Writer<support::little>(OS).write<uint32_t>(Bits);
       } else {
         support::endian::Writer<support::big>(OS).write<uint32_t>(Bits);
       }
       break;
     case 8:

lib/Target/PowerPC/PPCInstrInfo.td

def EH_SjLj_SetJmp32  : Pseudo<(outs gprc:$dst), (ins memr:$buf),
                           Requires<[In32BitMode]>;
   let isTerminator = 1 in
   def EH_SjLj_LongJmp32 : Pseudo<(outs), (ins memr:$buf),
                             "#EH_SJLJ_LONGJMP32",
                             [(PPCeh_sjlj_longjmp addr:$buf)]>,
                           Requires<[In32BitMode]>;
 }
 
-let isBranch = 1, isTerminator = 1 in {
+let isBranch = 1, isTerminator = 1, Size = 0 in {
   def EH_SjLj_Setup : Pseudo<(outs), (ins directbrtarget:$dst),
                         "#EH_SjLj_Setup\t$dst", []>;
 }
 
 // System call.
 let PPC970_Unit = 7 in {
   def SC     : SCForm<17, 1, (outs), (ins i32imm:$lev),
                       "sc $lev", IIC_BrB, [(PPCsc (i32 imm:$lev))]>;