Access to siginfo for the signal from debugger

[David Xu]

Kostik Belousov wrote:
> On Thu, Jul 01, 2010 at 05:05:26PM -0400, John Baldwin wrote:
>> On Thursday 01 July 2010 09:42:17 am Kostik Belousov wrote:
>>> Hi,
>>> below is the patch that provides the debugger with access to siginfo
>>> of the signal that stopped the debuggee. This allows to see a lot more
>>> details for the cause of the process stop. E.g. you can see a fault
>>> address if process get SIGSEGV or SIGBUS, you can distinguish between
>>> breakpoint-generated SIGTRAP and non-breakpoint, whether the signal
>>> was send due to external event etc.
>>>
>>> The change to struct ptrace_lwpinfo is backward-compatible in the sense
>>> that programs that were compiled with old definition for the struct will
>>> work on new kernels.
>> Nice!  Does gdb "just work" with these changes or does it need patching as 
>> well?
> It should "just work", and my testing seems to confirm this. gdb uses
> PT_LWPINFO to enumerate the thread ids, and I checked it on mt process.
> 
> As I said, the change is ABI backward-compatible, i.e. you do not need
> even to recompile the old program for new kernel.
> 
> Sure, gdb cannot show additional available information without
> modifications.

Yes, you can add new fields to ptrace_lwpinfo without any problem.
To print new fields, you should change the function
fbsd_thread_signal_cmd in file
src/gnu/usr.bin/gdb/libgdb/fbsd-threads.c
after change, you just type 'thread signal' command in gdb to
show thread's signal info. The command is freebsd specific,
others may or may not have it.

Regards,
David Xu