Re: frame unwinding patches

[Milian Wolff <mail at milianw dot de>]

On Monday, April 3, 2017 11:23:25 PM CEST Jan Kratochvil wrote:
> On Mon, 03 Apr 2017 11:00:03 +0200, Milian Wolff wrote:
> > I just got a report from a colleague. As-is, elfutils would fail to unwind
> > from the following location in his application:
> > 
> > 0x1137ca4
> 
> > With the x86_64 patch applied, he got a proper backtrace:
>
> S/he has something wrong with the compiler.  With
> -fasynchronous-unwind-tables frame pointer unwinding is never needed
> and gcc defaults to -fasynchronous-unwind-tables on x86_64.
> 
> This is why I haven't implemented it originally as it only paper overs the
> real problem and it leads to unreliable backtraces in longterm.

Please reconsider:

- In the example above, the address points into libnvidia-glcore.so and as 
such not compiled by my colleague but rather provided by NVidia as a binary 
blob. When you only got a binary blob and have to make do with it, you cannot 
tell people to "just fix the compiler invocation".

- Some JIT compilers, like QV4, actually embed frame pointers into their 
dynamic code, but do not go the extra mile for generating DWARF data or 
asynchronous unwind tables. That is another case where the patches by Ulf 
excel and make elfutils much more useful.

Please, as a user of elfutils I strongly hope that this patch set gets 
accepted. In general, similar patches that make it more resilient in the face 
of broken setups should also at least get considered instead of right-out 
rejected because "something is broken". Things break all the time, but 
developers often have to live with the brokenness.

Cheers

-- 
Milian Wolff
mail@milianw.de
http://milianw.de