[PATCH 2/3] gdbserver/Windows: Fix "no program to debug" error
Pedro Alves
palves@redhat.com
Thu May 10 00:09:00 GMT 2018
On 05/04/2018 07:30 PM, Joel Brobecker wrote:
> Trying to start a program with GDBserver on Windows yields
> the following error:
>
> $ gdbserver.exe --once :4444 simple_main.exe
> Killing process(es): 5008
> No program to debug
> Exiting
>
> The error itself comes from the following code shortly after
> create_inferior gets called (in server.c::main):
>
> /* Wait till we are at first instruction in program. */
> create_inferior (program_path.get (), program_args);
> [...]
>
> if (last_status.kind == TARGET_WAITKIND_EXITED
> || last_status.kind == TARGET_WAITKIND_SIGNALLED)
> was_running = 0;
> else
> was_running = 1;
>
> if (!was_running && !multi_mode)
> error ("No program to debug");
>
> What happens is that the "last_status" global starts initialized
> as zeroes, which means last_status.kind == TARGET_WAITKIND_EXITED,
> and we expect create_inferior to be waiting for the inferior to
> start until reaching the SIGTRAP, and to set the "last_status"
> global to match that last event we received.
>
> I suspect this is an unintended side-effect of the following change...
>
> commit 2090129c36c7e582943b7d300968d19b46160d84
> Date: Thu Dec 22 21:11:11 2016 -0500
> Subject: Share fork_inferior et al with gdbserver
>
> ... which removes some code in server.c that was responsible for
> starting the inferior in a functin that was named start_inferior,
> and looked like this:
>
> signal_pid = create_inferior (new_argv[0], &new_argv[0]);
> [...]
> /* Wait till we are at 1st instruction in program, return new pid
> (assuming success). */
> last_ptid = mywait (pid_to_ptid (signal_pid), &last_status, 0, 0);
>
> The code has been transitioned to using fork_inferior, but sadly,
> only for the targets that support it. On Windows, the calls to wait
> setting "last_status" simply disappeared.
>
> This patch adds it back in the Windows-specific implementation of
> create_inferior.
>
> gdb/gdbserver/ChangeLog:
>
> * win32-low.c (win32_create_inferior): Add call to my_wait
> setting last_status global.
> ---
> gdb/gdbserver/win32-low.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/gdb/gdbserver/win32-low.c b/gdb/gdbserver/win32-low.c
> index db5dd49..7ed5fc5 100644
> --- a/gdb/gdbserver/win32-low.c
> +++ b/gdb/gdbserver/win32-low.c
> @@ -704,6 +704,10 @@ win32_create_inferior (const char *program,
>
> do_initial_child_stuff (pi.hProcess, pi.dwProcessId, 0);
>
> + /* Wait till we are at 1st instruction in program, return new pid
> + (assuming success). */
> + last_ptid = win32_wait (pid_to_ptid (current_process_id), &last_status, 0);
> +
> return current_process_id;
> }
Ah, I was confused about how this actually works, since
do_initial_child_stuff already waits until we're at the 1st
instruction of the program:
/* Flush all currently pending debug events (thread and dll list) up
to the initial breakpoint. */
while (1)
{
but after staring at this for a bit, I remembered/realized the
loop leaves the status pending in the 'cached_status' global.
So the patch LGTM as is.
Thanks,
Pedro Alves
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