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[ping] [PATCH 1/2] gdbserver: catch fetch registers error
- From: "Metzger, Markus T" <markus dot t dot metzger at intel dot com>
- To: "gdb-patches at sourceware dot org" <gdb-patches at sourceware dot org>
- Cc: Daniel Jacobowitz <drow at false dot org>, "Pedro Alves (palves at redhat dot com)" <palves at redhat dot com>
- Date: Tue, 3 Jan 2017 13:14:13 +0000
- Subject: [ping] [PATCH 1/2] gdbserver: catch fetch registers error
- Authentication-results: sourceware.org; auth=none
ping
> -----Original Message-----
> From: Metzger, Markus T
> Sent: Tuesday, December 6, 2016 4:55 PM
> To: gdb-patches@sourceware.org
> Cc: Daniel Jacobowitz <drow@false.org>
> Subject: [PATCH 1/2] gdbserver: catch fetch registers error
>
> When the PTRACE_PEEKUSER ptrace request to read registers fails, gdbserer
> throws
> an error that is caught in captured_main, where it causes a E01 error packet to
> be sent and gdbserer to quit (if --once was specified) or the event loop to be
> re-started (otherwise).
>
> We may get such ptrace errors when trying to fetch registers for an exited or
> running thread. There are checks in GDB that check those conditions and throw
> meaningful error messages before we could run into the above ptrace error,
> e.g. thread.c:validate_registers_access.
>
> I ran into a new case and, rather than adding another call to
> validate_registers_access in GDB, I propose to catch the error already when
> handling the 'g' packet in gdbserver and reply with an error packet - assuming
> that gdbserver's internal state is still intact.
>
> To not replace a meaningful error message with E01, I'm trying to generate a
> useful error message when the error is detected and the exception is thrown.
>
> It would look like this ...
>
> gdb) PASS: gdb.btrace/enable-running.exp: continue to breakpoint: cont to 44
> cont&
> Continuing.
> (gdb) PASS: gdb.btrace/enable-running.exp: cont&
> record btrace
> warning: Remote failure reply: E.Selected thread is running.
> warning: Remote failure reply: E.Selected thread is running.
>
> ... although in this particular case, I'm going to suppress the warning.
>
> To make this look a bit nicer, we could consider stripping the "E." or the
> entire "Remote failure reply: E." when (re-)throwing the error inside GDB in
> remote.c.
>
> CC: Daniel Jacobowitz <drow@false.org>
>
> 2016-12-06 Markus Metzger <markus.t.metzger@intel.com>
>
> gdbserver/
> * server.c (process_serial_event): Add TRY/CATCH.
> * linux-low.c (fetch_register): Improve error message.
> ---
> gdb/gdbserver/linux-low.c | 19 ++++++++++++++++++-
> gdb/gdbserver/server.c | 18 ++++++++++++++++--
> 2 files changed, 34 insertions(+), 3 deletions(-)
>
> diff --git a/gdb/gdbserver/linux-low.c b/gdb/gdbserver/linux-low.c
> index e3e372c..a942b87 100644
> --- a/gdb/gdbserver/linux-low.c
> +++ b/gdb/gdbserver/linux-low.c
> @@ -5692,7 +5692,24 @@ fetch_register (const struct usrregs_info *usrregs,
> (PTRACE_TYPE_ARG3) (uintptr_t) regaddr, (PTRACE_TYPE_ARG4)
> 0);
> regaddr += sizeof (PTRACE_XFER_TYPE);
> if (errno != 0)
> - error ("reading register %d: %s", regno, strerror (errno));
> + {
> + /* ESRCH could mean that the thread is not traced, exited, or is not
> + stopped. */
> + if (errno == ESRCH)
> + {
> + struct lwp_info *lwp = get_thread_lwp (current_thread);
> +
> + if (!lwp_is_stopped (lwp))
> + error (_("Selected thread is running."));
> +
> + if (lwp_is_marked_dead (lwp))
> + error (_("Selected thread has terminated."));
> + }
> +
> + /* Report a generic error if we could not determine the exact
> + reason. */
> + error (_("Could not read register %d: %s."), regno, strerror (errno));
> + }
> }
>
> if (the_low_target.supply_ptrace_register)
> diff --git a/gdb/gdbserver/server.c b/gdb/gdbserver/server.c
> index ef8dd03..3064b4f 100644
> --- a/gdb/gdbserver/server.c
> +++ b/gdb/gdbserver/server.c
> @@ -4132,8 +4132,22 @@ process_serial_event (void)
> write_enn (own_buf);
> else
> {
> - regcache = get_thread_regcache (current_thread, 1);
> - registers_to_string (regcache, own_buf);
> + TRY
> + {
> + regcache = get_thread_regcache (current_thread, 1);
> + registers_to_string (regcache, own_buf);
> + }
> + CATCH (exception, RETURN_MASK_ALL)
> + {
> + const char *message;
> +
> + message = exception.message;
> + if (message == NULL)
> + message = _("Reading registers failed.");
> +
> + sprintf (own_buf, "E.%s", message);
> + }
> + END_CATCH
> }
> }
> break;
> --
> 1.8.3.1
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