[LLVMdev] How to halt a program

[Victor Campos]

Hi, all,

    I managed to insert the assertion in my bytecode, but the result is not
really what I expected :(

    Let me do a quick recap: I am trying to instrument the bytecode with
some assertions, and to do this, I want to insert the abort() function into
the bytecode. The problem is that LLVM is creating a new abort() function,
instead of using the one that already exists in libc. Let me show my code to
add the abort into the code:

// Create abort function
FunctionType *AbortFTy = FunctionType::get(Type::getVoidTy(*context),
false);
Function *AbortF = Function::Create(AbortFTy, GlobalValue::ExternalLinkage,
"abort", &M);

// Call to abort function
CallInst *abort = CallInst::Create(AbortF, Twine(), assertfail);

// Add atributes to the abort call instruction: no return and no unwind
abort->addAttribute(~0, Attribute::NoReturn);
abort->addAttribute(~0, Attribute::NoUnwind);

// Unreachable instruction
new UnreachableInst(*context, assertfail);

So, my bytecode now looks like this one below:

define i32 @main() nounwind {
....
"assert fail":                                    ; preds = %bb1, %13, %bb,
%3, %entry
  call void @abort() noreturn nounwind
  unreachable
....
}

define void @abort() {
"assert fail":
  call void @abort() noreturn nounwind
  unreachable
}

But, in truth, what I really wanted to do is to create a bytecode like the
one below:

define i32 @main() nounwind {
....
bb2:                                              ; preds = %bb, %entry
  call void @abort() noreturn nounwind
  unreachable
}

declare void @abort() noreturn nounwind

So, could some of you tell me what I need to do to get this "declare void
@abort ..." into my bytecode, instead of the "define void @abort..."?

Thank you very much,

Victor

2011/8/19 Nick Lewycky <nicholas at mxc.ca>

> Victor Campos wrote:
> > Guys,
> >
> >      I would like to instrument the bytecode that LLVM produces with
> > assertions. I have written the instrumentation code manually, but I do
> > not know how to halt the program in case the assertion is false. I took
> > a look into the bytecode that LLVM produces for a program like:
> >
> > #include <stdlib.h>
> > int main() {
> >    exit(1);
> > }
> >
> > And it is like this:
> >
> > define i32 @main() nounwind {
> > entry:
> >    %retval = alloca i32                            ; <i32*> [#uses=1]
> >    %0 = alloca i32                                 ; <i32*> [#uses=0]
> >    %"alloca point" = bitcast i32 0 to i32          ; <i32> [#uses=0]
> >    call void @exit(i32 1) noreturn nounwind
> >    unreachable
> > return:                                           ; No predecessors!
> >    %retval1 = load i32* %retval                    ; <i32> [#uses=1]
> >    ret i32 %retval1
> > }
> >
> > So, what is the LLVM code to insert the call "call void @exit(i32 1)
> > noreturn nounwind"? I thought about something like:
> >
> > CallInst *abort = CallInst::Create(/*POINTER TO ABORT*/,
> > ArrayRef<Value*>(), Twine(), assertfail);
> > abort->addAttribute(~0, Attribute::NoReturn);
> > abort->addAttribute(~0, Attribute::NoUnwind);
> >
> > However, I do not know what to fill up in /*POINTER TO ABORT*/. Can
> > anyone help me?
>
> Something like:
>
> // Once, M = llvm::Module*, C = LLVMContext&:
> FunctionType *AbortFTy = FunctionType::get(Type::getVoidTy(C), false);
> Function *AbortF = Function::Create(AbortFTy,
> GlobalValue::ExternalLinkage, "abort", M);
>
> // Each call site:
> CallInst *abort = CallInst::Create(AbortF, ...
>
> Nick
>
> >
> > Thank you very much,
> >
> > Victor
> >
> >
> >
> > _______________________________________________
> > LLVM Developers mailing list
> > LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
> _______________________________________________
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