[Bug go/70787] No time and child info with -pg and gccgo

["vogt at linux dot vnet.ibm.com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70787

--- Comment #2 from Dominik Vogt <vogt at linux dot vnet.ibm.com> ---
The Go runtime seems to register a handler for SIGPROF even if it does not want
to profile.  So it always uninstalls the handler installed by Glibc on behalf
of the -pg option.  To me it looks like -pg actually enables the profiling from
libgo instead.  Some ways to circumvent this:

1) Don't install a SIGPROF handler in the Go runtime if another is already
installed (possibly emit a warning or a fatal error if the program attempts to
enable the Go profiling).
=> Simple to implement.

2) Install the SIGPROF handler on the fly when it's needed instead of
unconditionally at Go runtime startup.  Possibly emit a warning if an existing
signal handler is uninstalled in the process.
=> Cleanest solution.

3) Store the previous signal handler and call it at the start of the Go runtime
signal handler.  However, this introduces a number several problems (the Go
runtime won't notice if the original profiling code wants to uninstall the
handler or install a new one or it might overwrite the Go runtime handler;
also, the two profiling systems will probably not agree on a common timing
interval).
=> May allow to run Glibc and libgo profiling in parallel but probably has some
unfixable issues.