[LLVMdev] noreturn attribute on a call instruction vs noreturn on a function

[Kostya Serebryany]

Hi, 

Building the following C code I get a call instruction that has no noreturn attribute, while the function itself does have it. 

void foo(void **b) {

  __builtin_longjmp(b, 1);

}

define void @_Z3fooPPv(i8** %b) noreturn nounwind uwtable {

entry:

  %0 = bitcast i8** %b to i8*

  tail call void @llvm.eh.sjlj.longjmp(i8* %0)   <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<

  unreachable

}

declare void @llvm.eh.sjlj.longjmp(i8*) noreturn nounwind  <<<<<<<<<<<<<<<<<

I've hit this in asan where it checks the noreturn attribute in the call instruction, but not in the function object. 

Who is wrong here? Should asan also check noreturn in the called function? 

Thanks, 

--kcc 

[Duncan Sands]

Hi Kostya,

I think you should consider the call no-return if either the call or the
callee has the no-return attribute.

Ciao, Duncan.

>
> Thanks,
>
> --kcc
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[Kostya Serebryany]

On Wed, Nov 28, 2012 at 8:05 PM, Duncan Sands <bald...@free.fr> wrote:

Hi Kostya,

On 28/11/12 14:47, Kostya Serebryany wrote:

Hi,

Building the following C code I get a call instruction that has no noreturn
attribute, while the function itself does have it.

void foo(void **b) {
   __builtin_longjmp(b, 1);
}


define void @_Z3fooPPv(i8** %b) noreturn nounwind uwtable {
entry:
   %0 = bitcast i8** %b to i8*
   tail call void @llvm.eh.sjlj.longjmp(i8* %0)
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
   unreachable
}

declare void @llvm.eh.sjlj.longjmp(i8*) noreturn nounwind  <<<<<<<<<<<<<<<<<


I've hit this in asan where it checks the noreturn attribute in the call
instruction, but not in the function object.
Who is wrong here? Should asan also check noreturn in the called function?

I think you should consider the call no-return if either the call or the
callee has the no-return attribute.

Thanks, I've fixed this in asan pass. 

--kcc 

[Nuno Lopes]

You can use CallInst::hasFnAttr(). It checks for attributes in the
instruction and in the function decl.

http://llvm.org/docs/doxygen/html/Instructions_8cpp_source.html#l00345

Nuno

[Kostya Serebryany]

On Fri, Nov 30, 2012 at 2:21 AM, Nuno Lopes <nunop...@sapo.pt> wrote:

You can use CallInst::hasFnAttr().  It checks for attributes in the instruction and in the function decl.

Indeed.... 

And we have 

    bool doesNotReturn() const { return hasFnAttr(Attributes::NoReturn); }

and asan code called CI->doesNotReturn  and it did not work, but now it works. 

Hmm. 

Anyway, thanks! 

--kcc