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Re: RFC: A mode in which gdb avoids libthread_db
On Sat, Jul 26, 2003 at 07:37:12PM -0400, Elena Zannoni wrote:
> Daniel Jacobowitz writes:
> > Recent Linux kernels (2.5.30 and later; theoretically the latest Red Hat
> > 2.4.20 kernels also include it, but I observed some badness in testing...)
> > support some ptrace extensions I designed which make it possible to debug
> > multi-threaded applications without using libthread_db at all. The only
> > things we'll lose are:
> > - Potential high-level information, like mutex status - right now we
> > don't have this at all on GNU/Linux.
> > - TLS access - this could be easily fixed by handling each platform's
> > TLS ABI directly from GDB, and there's a comment to that effect in
> > GDB's source already.
> > - TIDs - we'd only have the application's LWP IDs, not the thread IDs
> > that LinuxThreads/NPTL use.
> >
> > Things we'll gain:
> > - A lot of libthread_db-related bugs would go away. For instance,
> > the kfail in print-threads.exp, which hits a breakpoint after
> > LinuxThreads decides the thread has already exited.
> > - ABI simplicity - this would solve the x86-64/i386 issue, and similar
> > problems on MIPS.
> > - Support for debugging clone-based 1-1 threading which doesn't use
> > libpthread.so.
> >
> > Once the pending fork-debugging patch is accepted, most of the machinery
> > we'd need to do it will be in place, too. Thoughts? Worthwhile?
>
>
> I know first hand of the pains of mismatched glibcs, binutils,
> kernels, gdbs. I wouldn't mind having this coexist with the use of
> glibc, is that possible?
Sure. It could just be a switch or a "set" flag - easy enough.
> What ptrace changes did you do? (Elena needs to start reading
> linux-kernel)
Take a look at the support for "set follow-fork-mode", which I've
posted a few times. I added:
/* 0x4200-0x4300 are reserved for architecture-independent additions. */
#define PTRACE_GETEVENTMSG 0x4201
#define PTRACE_GETSIGINFO 0x4202
#define PTRACE_SETSIGINFO 0x4203
/* options set using PTRACE_SETOPTIONS */
#define PTRACE_O_TRACEFORK 0x00000002
#define PTRACE_O_TRACEVFORK 0x00000004
#define PTRACE_O_TRACECLONE 0x00000008
#define PTRACE_O_TRACEEXEC 0x00000010
#define PTRACE_O_TRACEVFORKDONE 0x00000020
#define PTRACE_O_TRACEEXIT 0x00000040
They allow a debugger to automatically detect processes as they're
created, and better signal handling.
--
Daniel Jacobowitz
MontaVista Software Debian GNU/Linux Developer