Re: "tracepoints", "follow-fork-mode", "watch - remote"

[Michael Snyder <msnyder at redhat dot com>]

"Sarnath K - CTD, Chennai." wrote:
> 
> Hi,
> 
> > I didn't want to say that you should run the progream after.
> > Simply comparing the address of the xbreak with
> > the position of the ret instruction
> > in the function disassembly is enough to
> > show that you are right in saying that this
> > command is buggy for i386 at least.

XBREAK is buggy for all targets, possibly excepting hpux.  
It should never have been added, and it will be removed 
as soon as I can find the time.

> 
>   Fine Pierre. You are right.
> I am not sure about the pointers you gave in
> the "sources". I dont have acquaintance with
> at the source level.
> 
> And I have 3 more doubts ;)
> I am running GDB 5.1, Pentium III as I had told b4.
> 
> 1. This is about tracepoints.

Tracepoints will not work unles you have a gdb stub that
supports them.

> I tried setting "tracepoints" and dumping snapshots.
> But unfortunately I am not able to do it. For the
> commands "tstart" and "tstop"  GDB says that
> "Trace can only be run on remote targets.". so I just
> "run" the program. The program executed and exited
> normally. I followed the instructions from "onlinedocs"
> in http://sources.redhat.com. I am not able to dump any
> snapshots. ;(
> 
> This is a snapshot of the system:
> 
> Program Source:
> 
> [root@via1 gdb]# cat trace.c
> int collected_data;
> 
> int main()
> {
>         collected_data = 3;
>         a();
> }
> 
> int a()
> {
>         return 0;
> }
> [root@via1 gdb]#
> 
> Compilation:
> [root@via1 gdb]# cc -g -o trace trace.c
> [root@via1 gdb]#
> 
> GDB Session:
> 
> [root@via1 gdb]# ./gdb ./trace
> GNU gdb 5.1
> Copyright 2001 Free Software Foundation, Inc.
> GDB is free software, covered by the GNU General Public License, and you are
> welcome to change it and/or distribute copies of it under certain
> conditions.
> Type "show copying" to see the conditions.
> There is absolutely no warranty for GDB.  Type "show warranty" for details.
> This GDB was configured as "i686-pc-linux-gnu"...
> (gdb) trace a
> Tracepoint 1 at 0x80483b7: file trace.c, line 11.
> (gdb) actions
> Enter actions for tracepoint 1, one per line.
> End with a line saying just "end".
> > collect collected_data
> > end
> (gdb) tstart
> Trace can only be run on remote targets.
> (gdb) run
> Starting program: /home/via/sarnath/gdb/./trace
> 
> Program exited normally.
> (gdb) tdump
> Trace can only be run on remote targets.
> (gdb) tfind 1
> Trace can only be run on remote targets.
> (gdb)
> 
> So, Can't I trace on a standalone system.
> If I use "gdbserver" as on the target side,
> GDB says that "target doesnt support command".
> So whats the solution ? Cant "tracepoints" be
> used ?

Not unles you have a stub that supports them.


> 2. hardware brkpoints, hardware "watch"es are
>    not supported in the GDBSERVER. Is this true ?
>    or Is there any configutation option for this, which
>    I am missing ?
>    (PIII machine)
> 
> 3. "set follow-fork-mode" always works as if it's value
>    is "parent". I am not able to debug "child" or enable
>    GDB "ask" for the choice. Is this configuraion, not
>    supported on x86 machines or Am I missing something.

Follow-fork is also a command that will not work anywhere
except possibly HPUX.


> /*
>  * I am relatively new to GDB envmt. I am just
>  * learning the different features.
>  * So if I am using GDB in a wrong way, please
>  * let me know and ignore this mail.
>  */
> 
> Sarnath