Re: No useful callgraphs on Fedora 27

[Christian Hergert <christian hergert me>]

On 02/11/2018 07:08 AM, Clemens Eisserer wrote:
> Isn't -fomit-framepointer the default for amd64 ABI?

There was a real savings for 32-bit x86, but for x86_64 not so much.

If you have public ABI you're calling in a library, perf can usually get
that data just fine. But if you hit something like a JS runtime (which
doesn't use a traditional stack) you're completely out of luck without
coordination from the runtime.

gdb can walk the stack in many cases because it has enough information
to figure things out (even though that requires executing code). The
kernel doesn't currently employ so many heuristics for various safety
reasons.

I'm not up to date on ORC (the new kernel unwinder) for the Linux
kernel, but one could reasonably assume that the kernel getting a more
advanced stack unwinder would be a benefit for us.

Since you've mentioned debian, you may want to see if debian testing
works better. I know Debian had miss-packaged¹ Sysprof for quite a while
and I do not know if their fixes made it from unstable→testing→stable.

-- Christian

¹ they didn't actually ship sysprofd properly which is what does all our
syscalls which require elevated privs