Bug#767756: glibc: Consider providing a libc build compiled with -fno-omit-frame-pointer to help with profiling

[notafile <debbugs@notafile.com>]

On Sun, Feb 16, 2020, at 14:15, Florian Weimer wrote:
> Most unwinders should be able to use asynchronous unwind tables, which
> only impact disk size (and the size of VM mappings).

Experience with perf shows orders of magnitude of overhead of DWARF unwinding over fp based unwinding. The kernel uses ORC for this reason, which is up to 20-40x faster than DWARF, in addition to the removal of the 5-10% DWARF performance penalty caused by .text size increase. It is however not available for user-space programs. Since it uses ORC, DWARF unwinding is also unavailable in (and unlikely to be ever supported by) the kernel, including the bpf_get_stack* helpers used in eBPF. Since most interaction with the kernel is done through libc, this unfortunately makes it impossible to meaningfully inspect user-space programs in response to events, which is one of the biggest selling points of bpf tracing.