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Re: [Qemu-devel] [6095] User-mode GDB stub improvements - handle fork
From: |
Martin Mohring |
Subject: |
Re: [Qemu-devel] [6095] User-mode GDB stub improvements - handle fork |
Date: |
Tue, 06 Jan 2009 17:19:15 +0100 |
User-agent: |
Thunderbird 2.0.0.18 (X11/20081112) |
I seem to have found the cause, why ARM user mode with nptl does not
work as before. see below.
Martin
Aurelien Jarno wrote:
> Revision: 6095
> http://svn.sv.gnu.org/viewvc/?view=rev&root=qemu&revision=6095
> Author: aurel32
> Date: 2008-12-18 22:44:04 +0000 (Thu, 18 Dec 2008)
>
> Log Message:
> -----------
> User-mode GDB stub improvements - handle fork
>
> Close gdbserver in child processes, so that only one stub tries to talk
> to GDB at a time. Updated from an earlier patch by Paul Brook.
>
> Signed-off-by: Daniel Jacobowitz <address@hidden>
> Signed-off-by: Aurelien Jarno <address@hidden>
>
> Modified Paths:
> --------------
> trunk/gdbstub.c
> trunk/gdbstub.h
> trunk/linux-user/main.c
> trunk/linux-user/syscall.c
>
> Modified: trunk/gdbstub.c
> ===================================================================
> --- trunk/gdbstub.c 2008-12-18 22:43:56 UTC (rev 6094)
> +++ trunk/gdbstub.c 2008-12-18 22:44:04 UTC (rev 6095)
> @@ -1996,6 +1996,18 @@
> gdb_accept();
> return 0;
> }
> +
> +/* Disable gdb stub for child processes. */
> +void gdbserver_fork(CPUState *env)
> +{
> + GDBState *s = gdbserver_state;
> + if (s->fd < 0)
> + return;
> + close(s->fd);
> + s->fd = -1;
> + cpu_breakpoint_remove_all(env, BP_GDB);
> + cpu_watchpoint_remove_all(env, BP_GDB);
> +}
>
In case of USE_NPTL is defined, it seems that either s or env can be
NULL, so I get a exception (yes, nptl works on arm in user mode).
My understanding is that this might be a race condition of the first
fork() call coming even before env or gdbserver_state is initialised
towards !NULL.
> #else
> static int gdb_chr_can_receive(void *opaque)
> {
>
> Modified: trunk/gdbstub.h
> ===================================================================
> --- trunk/gdbstub.h 2008-12-18 22:43:56 UTC (rev 6094)
> +++ trunk/gdbstub.h 2008-12-18 22:44:04 UTC (rev 6095)
> @@ -13,6 +13,7 @@
> int gdb_handlesig (CPUState *, int);
> void gdb_exit(CPUState *, int);
> int gdbserver_start(int);
> +void gdbserver_fork(CPUState *);
> #else
> int gdbserver_start(const char *port);
> #endif
>
> Modified: trunk/linux-user/main.c
> ===================================================================
> --- trunk/linux-user/main.c 2008-12-18 22:43:56 UTC (rev 6094)
> +++ trunk/linux-user/main.c 2008-12-18 22:44:04 UTC (rev 6095)
> @@ -162,6 +162,7 @@
> pthread_cond_init(&exclusive_cond, NULL);
> pthread_cond_init(&exclusive_resume, NULL);
> pthread_mutex_init(&tb_lock, NULL);
> + gdbserver_fork(thread_env);
>
This gdbserver_fork(thread_env) call then causes the exception.
- Re: [Qemu-devel] [6095] User-mode GDB stub improvements - handle fork,
Martin Mohring <=