Re: gdb + sigtraps

[Wolfgang Solfrank <Wolfgang%Solfrank.net@localhost>]

Hi,

> When trying to debug my favorite program dasher on -current/amd64 using
> gdb, I keep getting sigtraps. This makes life difficult, but seems to be
> "recent". e.g.,
> gdb dasher
> break sendText
> c
> now I will get sigtraps, keep continuing until my break point is reached
> s
> and we are back to sigtraps and I can't step to the next line...
> This isn't what used to happen...
>
> Any ideas where to look?

AFAICT this happens only with programs using multithreading.  Somehow
gdb gets confused by the traps (single step and/or breakpoint) that it
itself triggers in the debuggee.

Actually, debugging multithreaded programs using gdb doesn't work as
expected since at least November 2007, when the pthread structure grew
a member in front of pt_magic, while the pthread_dbg library wasn't
adapted to that change.  And in the meantime, it grew another member.
I fixed that already in my own tree, but while helping a bit, this
isn't enough to make gdb work reliably again on multithreaded programs.
I'm investigating this further.

I am not sure about the purpose of the pthread_dbg library anyway.
On one side it is way to intertwined with gdb internals to allow
for adaption to another debugger.  If on the other side the placement
of libpthread_dbg alongside libpthread in our source tree was to
encourage anyone changing libpthread to also do the accompanying
changes to libpthread_dbg, this obviously didn't work out.  Or was
this simply separated from gdb sources due to license reasons?

Ciao,
Wolfgang
--
Wolfgang%Solfrank.net@localhost                         Wolfgang Solfrank