Re: F37 proposal: Add -fno-omit-frame-pointer to default compilation flags (System-Wide Change proposal)

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> https://fedoraproject.org/wiki/Changes/fno-omit-frame-pointer
> [...]
> === Unwinding ===
> [...]
> * Kernel 4.8 frame pointer benchmarks by Suse showed 5%-10%
> regressions in some benchmarks
> (https://lore.kernel.org/all/20170602104048.jkkzssljsompjdwy@xxxxxxx/T/#u)

Regressions of such magnitude can veto such changes, especially when
they hit everyone, not just those who are highly dependent on the
profiling tools the proposal is concerned about.


> === Alternatives to frame pointers ===
>
> There are a few alternative ways to unwind stacks instead of using the
> frame pointer:

> * [https://dwarfstd.org DWARF] data - The compiler can emit extra
> [...] The problem is that we need to unwind the stack in kernel space

(Are you referring to a novel kernel-resident tool?)


> To summarize, if we want complete stacks with reasonably low overhead
> (which we do, there's no other way to get accurate profiling data from
> running services), frame pointers are currently the best option.

The proposal doesn't characterize the "reasonably low overhead" that
this operation targets.  That makes it hard to judge the tradeoffs.


> [...]
> Fedora users will be more likely to have a streamlined experience when
> trying to debug/profile system executables/libraries. Tools such as
> perf will work out of the box instead of requiring to users to provide
> extra options (e.g. --call-graph=dwarf/LBR) [...]

If typing that option were a hardship, it could be made default on
Fedora.  With broad debuginfod auto-downloading capability, maybe it's
worth considering.


- FChE
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