GDB to debug threaded application

GDB to debug threaded application

[Micha Nelissen]

Hi all,

I have built a cross-toolchain (x86-64 to arm, gcc 5.4.0) with musl 
(1.1.16) using buildroot (2017.02). I let buildroot build a gdb for the 
arm platform. It runs, but when I debug my application, gdb hangs after 
a thread is started. Can't interrupt it, have to kill -KILL my 
application from another ssh session.

I noticed that there is a libthread_db.so in the glibc-based toolchain. 
Do I need something similar for musl? That libthread_db.so needs 
libc.so.6 (glibc) so I guess I can't use it as-is?

Thanks for any pointers!

Micha

Re: GDB to debug threaded application

[Rich Felker]

On Fri, Apr 06, 2018 at 06:33:35PM +0200, Micha Nelissen wrote:
> Hi all,
> 
> I have built a cross-toolchain (x86-64 to arm, gcc 5.4.0) with musl
> (1.1.16) using buildroot (2017.02). I let buildroot build a gdb for
> the arm platform. It runs, but when I debug my application, gdb
> hangs after a thread is started. Can't interrupt it, have to kill
> -KILL my application from another ssh session.
> 
> I noticed that there is a libthread_db.so in the glibc-based
> toolchain. Do I need something similar for musl? That
> libthread_db.so needs libc.so.6 (glibc) so I guess I can't use it
> as-is?
> 
> Thanks for any pointers!

No, musl does not use libthread_db.so, but presence of a glibc version
of this library could break things badly. Make sure it's not being
built or present in any location gdb might search. Are you using a
remote/cross gdb (with gdbserver on the target) or local gdb?

Rich

Re: GDB to debug threaded application

[Micha Nelissen]

On 6 Apr 2018, at 19:22, Rich Felker <dalias@libc.org> wrote:
> 
>> On Fri, Apr 06, 2018 at 06:33:35PM +0200, Micha Nelissen wrote:
>> Hi all,
>> 
>> I have built a cross-toolchain (x86-64 to arm, gcc 5.4.0) with musl
>> (1.1.16) using buildroot (2017.02). I let buildroot build a gdb for
>> the arm platform. It runs, but when I debug my application, gdb
>> hangs after a thread is started. Can't interrupt it, have to kill
>> -KILL my application from another ssh session.
>> 
>> I noticed that there is a libthread_db.so in the glibc-based
>> toolchain. Do I need something similar for musl? That
>> libthread_db.so needs libc.so.6 (glibc) so I guess I can't use it
>> as-is?
>> 
>> Thanks for any pointers!
> 
> No, musl does not use libthread_db.so, but presence of a glibc version
> of this library could break things badly. Make sure it's not being
> built or present in any location gdb might search. Are you using a
> remote/cross gdb (with gdbserver on the target) or local gdb?

A local gdb. In the buildroot environment, no libthread_db is present I think.

Micha

Re: GDB to debug threaded application

[Rich Felker]

On Fri, Apr 06, 2018 at 11:00:48PM +0200, Micha Nelissen wrote:
> On 6 Apr 2018, at 19:22, Rich Felker <dalias@libc.org> wrote:
> > 
> >> On Fri, Apr 06, 2018 at 06:33:35PM +0200, Micha Nelissen wrote:
> >> Hi all,
> >> 
> >> I have built a cross-toolchain (x86-64 to arm, gcc 5.4.0) with musl
> >> (1.1.16) using buildroot (2017.02). I let buildroot build a gdb for
> >> the arm platform. It runs, but when I debug my application, gdb
> >> hangs after a thread is started. Can't interrupt it, have to kill
> >> -KILL my application from another ssh session.
> >> 
> >> I noticed that there is a libthread_db.so in the glibc-based
> >> toolchain. Do I need something similar for musl? That
> >> libthread_db.so needs libc.so.6 (glibc) so I guess I can't use it
> >> as-is?
> >> 
> >> Thanks for any pointers!
> > 
> > No, musl does not use libthread_db.so, but presence of a glibc version
> > of this library could break things badly. Make sure it's not being
> > built or present in any location gdb might search. Are you using a
> > remote/cross gdb (with gdbserver on the target) or local gdb?
> 
> A local gdb. In the buildroot environment, no libthread_db is present I think.

Can you reproduce this behavior (the hang) with a trivial test program
that starts a thread, or does it only happen with your real
application?

Rich