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Re: Forbid __builtin_return_address when inlining
Mark Mitchell writes:
> 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
No kidding. Yes, that's surely possible.
> 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
No, not really. Java methods sometimes need to find their caller, and
I was testing that when I discovered this anomalous behaviour when a
method was being inlined. The most obvious solution is for the Java
FE to mark the methods that need to find their caller noinline, and
that's what I'll do.