Re: Timer

["Marc Brünink" <marc@nus.edu.sg>]

On May 7, 2013, at 12:43 PM, Doug Evans wrote:

> On Mon, May 6, 2013 at 2:52 AM, Marc Brünink <marc@nus.edu.sg> wrote:
>> I want to execute a piece of code at regular intervals. Actually I'm sampling $pc.
>> (let's not go into detail why I use gdb)
>> 
>> My current solution just starts another process that sends a SIGTRAP to the debugged application. Using a simple script I can print the $pc.
>> 
>> However, I just realised that this approach does not work too well. If gdb is stopped due to a breakpoint it will interpret the received SIGTRAP as another hit of the very same breakpoint.
>> 
>> Reproduce:
>> 1. Attach to any program
>> 2. Create any breakpoint
>> 3. Wait until breakpoint is hit
>> 4. Send SIGTRAP to debugged application
>> 5. continue
>> 
>> Actually, now that I think about it, I should have anticipated this behaviour.
>> Is there a better way to execute a piece of code at regular intervals?
> 
> bash$ man setitimer

I suppose you are suggesting to modify either GDB or the application. This is exactly what I don't want. Any other way to accomplish this (using gdb)?

Marc
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Date: Tue, 07 May 2013 07:33:00 -0000
From: Yao Qi <yao@codesourcery.com>
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To: Suchakra Sharma <suchakrapani.sharma@polymtl.ca>
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Subject: Re: Debugging agent library
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Hello,
Suchakra,

On 05/07/2013 03:21 AM, Suchakra Sharma wrote:
> Hi,
>
> We tried to find out how to use the debugging agent library here [1] but
> were unsuccessful. As of now, we have built a test app linked to dagent

It would be nice if you post some details about how you use dagent and
the error message you got.

> which creates a socket file and expects commands. We wish to use it with
> GDB as well as other applications to primarily objective of tracing
> using GDB's fast tracepoint infra. Any help in this regard will be
> appreciated.
>
> [1] https://github.com/MentorEmbedded/Debug-Agent-Library/wiki
>

I checked out the wiki and realize that the existing documentation has
an assumption that readers are much familiar with GDB and GDB
tracepoint.  The session below shows how to install fast tracepoint
through dagent.

In one console, start the program in GDBserver,

$ LD_PRELOAD=/install/lib/libdagent.so ./gdbserver/gdbserver :1234
./testsuite/gdb.base/break

In the other console, start GDB and connect to GDBserver,

$ ./gdb ./testsuite/gdb.base/break
(gdb) target remote :1234
(gdb) b main
(gdb) c

(gdb) b marker4  // set breakpoint to make sure program doesn't exit
(gdb) ftrace *0x0804851e // set fast tracepoint at certain address
(gdb) set agent on   // enable agent
(gdb) tstart         // start tracing
(gdb) c
(gdb) tstop          // stop tracing
(gdb) tfind          // examine the trace frames tracepoint collects
Found trace frame 0, tracepoint 3
#0  main (argc=<unavailable>, argv=<unavailable>, envp=<unavailable>) at
../../../../git/gdb/testsuite/gdb.base/break.c:94
94          marker1 ();  /* set breakpoint 11 here */

Let me know if you get something else or obviously wrong.

--
Yao (齐尧)