llvm dev - Jul 2010 - [LLVMdev] Why clang++ doesn't set 'noreturn' flag on declarations of __cxa_throw and _Unwind_Resume_or_Rethrow ?

When I compile some code with the near-trunk clang++ I get this:
...
   tail call void @_Unwind_Resume_or_Rethrow(i8* %exn2) noreturn
   unreachable
...
declare void @_Unwind_Resume_or_Rethrow(i8*)
...

Same with __cxa_throw. 'noreturn' is missing on declarations.
This seems to be a bug.

Also can _Unwind_Resume_or_Rethrow actually return? When I run some 
simple exception code in JIT I see that this function actually returns 
and then SEGVs.

Yuri

On Jul 15, 2010, at 3:31 PM, Yuri wrote:
> When I compile some code with the near-trunk clang++ I get this:
Please send clang-specific questions to cfe-dev at cs.uiuc.edu.
> ...
>   tail call void @_Unwind_Resume_or_Rethrow(i8* %exn2) noreturn
>   unreachable
> ...
> declare void @_Unwind_Resume_or_Rethrow(i8*)
> ...
> 
> Same with __cxa_throw. 'noreturn' is missing on declarations.
> This seems to be a bug.
It really shouldn't make a difference;  the call site should take priority
anyway.
> Also can _Unwind_Resume_or_Rethrow actually return? When I run some 
> simple exception code in JIT I see that this function actually returns 
> and then SEGVs.
I have no idea what system you're on, but _Unwind_Resume_or_Rethrow really
isn't allowed to return.

John.

On Jul 15, 2010, at 5:51 PM, John McCall wrote:
>> Also can _Unwind_Resume_or_Rethrow actually return? When I run some 
>> simple exception code in JIT I see that this function actually returns 
>> and then SEGVs.
> 
> I have no idea what system you're on, but _Unwind_Resume_or_Rethrow
really
> isn't allowed to return.
> 
It's not. But if the unwind library can't handle something, then the
_Unwind_Resume_or_Rethrow could fall out of the function (it would assert in
debug mode). Darwin's implementation of _URoR in libunwind does this.

-bw