Re: Forbid __builtin_return_address when inlining

[Mark Mitchell <mark at codesourcery dot com>]

Andrew Haley wrote:
> Mark Mitchell writes:
>  > Andrew Haley wrote:
>  > > __builtin_return_address(0) returns the wrong address if its caller
>  > > has been inlined.  Weirdly, we never seem to have detected this
>  > > before, but it surely must be wrong.
>  > 
>  > The manual says:
>  > 
>  > >  When
>  > >      inlining the expected behavior is that the function will return
>  > >      the address of the function that will be returned to.  To work
>  > >      around this behavior use the `noinline' function attribute.
>  > 
>  > which seems to suggest that the behavior you are seeing as is
>  > documented, peculiar though it seems.
> 
> Hmm, OK.  But if I fixed the peculiar behavour then I could also
> remove the peculiar documentation, couldn't I?  That would surely be
> an improvement.,,

The problem is that we don't know how people may already be using this
"feature".  Since someone bothered to document it, I wouldn't be
surprised if something (the Linux kernel?  a scripting language
interpreter?) is using it in some way that depends on the current behavior.

So, I fully agree that the semantics you're proposing seem more sensible
(i.e., tell me where *this function* returns, and, if necessary, make
sure that it has somewhere to return to by not inlining it), but I'd be
nervous about making the change.  Is there a compelling reason to change
this, other than just that it makes sense?

-- 
Mark Mitchell
CodeSourcery
mark@codesourcery.com
(650) 331-3385 x713