Re: [PATCH] gdbserver: When attaching, add process before lwps

[Pedro Alves <palves@redhat.com>]

On 01/25/2019 10:48 AM, Alan Hayward wrote:
> The recent BP/WP changes for AArch64 swapping the order in add_lwp()
> so that the process was added before the lwp. This was due to the lwp
> creation requiring the process data.
> 
> This also needs changing in linux_attach().
> 
> Fixes gdb.server/ext-attach.exp on Aarch64.
> 
> (This regression was hidden due to the racy nature of the gdb.server
> tests - now they are no longer racy it'll be easier to spot. Also
> checked X86).
> 
> gdb/gdbserver/ChangeLog:
> 
> 2019-01-25  Alan Hayward  <alan.hayward@arm.com>
> 
> 	* linux-low.c (linux_attach): Add process before lwp.

> ---
>  gdb/gdbserver/linux-low.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c
> index 17cce24d76..1ab2cfb1eb 100644
> --- a/gdb/gdbserver/linux-low.c
> +++ b/gdb/gdbserver/linux-low.c
> @@ -1188,6 +1188,8 @@ linux_attach (unsigned long pid)
>    ptid_t ptid = ptid_t (pid, pid, 0);
>    int err;
>  
> +  proc = linux_add_process (pid, 1);
> +
>    /* Attach to PID.  We will check for other threads
>       soon.  */
>    err = linux_attach_lwp (ptid);
> @@ -1198,8 +1200,6 @@ linux_attach (unsigned long pid)
>        error ("Cannot attach to process %ld: %s", pid, reason.c_str ());
>      }
>  
> -  proc = linux_add_process (pid, 1);
> -

This fails to consider the error conditions.  That error call
visible above throws an exception.

- If GDBserver is already attached to the process, this will
  create another process_info object for the already-attached
  process, and leave it behind.

  For this case, it would seem better to check whether we're
  already attached to a given PID in common code, around
  server.c:attach_inferior.

- If GDBserver isn't already attached, but the attach fails,
  this will likewise leave a stale process_info object behind.

Thanks,
Pedro Alves