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Change the marker byte for stubs from 0xcd to 0xce (another form of

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interrupt instruction, which shouldn't arise any other way).  0xcd is
also used by JITMemoryManager to initialize the buffer to garbage,
which means it could appear following a noreturn call even when
that is not a stub, confusing X86CompilationCallback2.  PR 4929.

llvm-svn: 81888
This commit is contained in:
Dale Johannesen 2009-09-15 18:32:14 +00:00
parent 0f1da52ad1
commit d00219c590
1 changed files with 6 additions and 3 deletions
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9
lib/Target/X86/X86JITInfo.cpp
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@ -338,7 +338,7 @@ X86CompilationCallback2(intptr_t *StackPtr, intptr_t RetAddr) {
"Could not find return address on the stack!");
// It's a stub if there is an interrupt marker after the call.
bool isStub = ((unsigned char*)RetAddr)[0] == 0xCD;
bool isStub = ((unsigned char*)RetAddr)[0] == 0xCE;
// The call instruction should have pushed the return value onto the stack...
#if defined (X86_64_JIT)
@ -377,7 +377,7 @@ X86CompilationCallback2(intptr_t *StackPtr, intptr_t RetAddr) {
// If this is a stub, rewrite the call into an unconditional branch
// instruction so that two return addresses are not pushed onto the stack
// when the requested function finally gets called. This also makes the
// 0xCD byte (interrupt) dead, so the marker doesn't effect anything.
// 0xCE byte (interrupt) dead, so the marker doesn't effect anything.
#if defined (X86_64_JIT)
// If the target address is within 32-bit range of the stub, use a
// PC-relative branch instead of loading the actual address. (This is
@ -480,7 +480,10 @@ void *X86JITInfo::emitFunctionStub(const Function* F, void *Fn,
JCE.emitWordLE((intptr_t)Fn-JCE.getCurrentPCValue()-4);
#endif
JCE.emitByte(0xCD); // Interrupt - Just a marker identifying the stub!
// This used to use 0xCD, but that value is used by JITMemoryManager to
// initialize the buffer with garbage, which means it may follow a
// noreturn function call, confusing X86CompilationCallback2. PR 4929.
JCE.emitByte(0xCE); // Interrupt - Just a marker identifying the stub!
return JCE.finishGVStub(F);
}