Re: Always run GDB command post-hook after pre-hook has been run

[Stephen Cross <scross at undo-software dot com>]

Hi Pedro,

Here's a patch that adds 'hookerror-' to GDB. This passes the test suite
(running 'make check' in the 'gdb' directory).

Do you think this patch is acceptable? Are there any further changes that you'd
like me to make?

Thanks,
Stephen

--------------------------------------------------------------------------------

[PATCH] Add command error hooks using 'hookerror-'.

* cli-decode.c: Add errorhook args to delete_cmd().
* cli-decode.h: Add hook_error field to cmd_list_element.
* cli-script.c: Add execute_cmd_error_hook(). Match 'hookerror-' string.
* command.h: Declare execute_cmd_error_hook().
* top.c: Call error hook if command throws exception.
* testsuite/gdb.base/define.exp: Add test cases for 'hookerror-'.
---
 gdb/ChangeLog                     | 10 ++++++++
 gdb/cli/cli-decode.c              | 35 ++++++++++++++++++++++------
 gdb/cli/cli-decode.h              |  7 ++++++
 gdb/cli/cli-script.c              | 28 +++++++++++++++++++++-
 gdb/command.h                     |  5 ++--
 gdb/doc/gdb.texinfo               | 19 +++++++++++----
 gdb/testsuite/gdb.base/define.exp | 49 +++++++++++++++++++++++++++++++++++++++
 gdb/top.c                         | 18 +++++++++++++-
 8 files changed, 156 insertions(+), 15 deletions(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index d6b4a6b..6eb0c13 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,13 @@
+2016-02-24  Stephen Cross <scross@undo-software.com>
+
+    Add command error hooks using 'hookerror-'.
+    * cli-decode.c: Add errorhook args to delete_cmd().
+    * cli-decode.h: Add hook_error field to cmd_list_element.
+    * cli-script.c: Add execute_cmd_error_hook(). Match 'hookerror-' string.
+    * command.h: Declare execute_cmd_error_hook().
+    * top.c: Call error hook if command throws exception.
+    * testsuite/gdb.base/define.exp: Add test cases for 'hookerror-'.
+
 2016-02-24  Joel Brobecker  <brobecker@adacore.com>

     GDB 7.11 released.
diff --git a/gdb/cli/cli-decode.c b/gdb/cli/cli-decode.c
index 04ed6ab..c143d5a 100644
--- a/gdb/cli/cli-decode.c
+++ b/gdb/cli/cli-decode.c
@@ -33,7 +33,9 @@ static struct cmd_list_element *delete_cmd (const char *name,
                         struct cmd_list_element **prehook,
                         struct cmd_list_element **prehookee,
                         struct cmd_list_element **posthook,
-                        struct cmd_list_element **posthookee);
+                        struct cmd_list_element **posthookee,
+                        struct cmd_list_element **errorhook,
+                        struct cmd_list_element **errorhookee);

 static struct cmd_list_element *find_cmd (const char *command,
                       int len,
@@ -198,7 +200,8 @@ add_cmd (const char *name, enum command_class
theclass, cmd_cfunc_ftype *fun,
   /* Turn each alias of the old command into an alias of the new
      command.  */
   c->aliases = delete_cmd (name, list, &c->hook_pre, &c->hookee_pre,
-               &c->hook_post, &c->hookee_post);
+               &c->hook_post, &c->hookee_post, &c->hook_error,
+               &c->hookee_error);
   for (iter = c->aliases; iter; iter = iter->alias_chain)
     iter->cmd_pointer = c;
   if (c->hook_pre)
@@ -209,6 +212,10 @@ add_cmd (const char *name, enum command_class
theclass, cmd_cfunc_ftype *fun,
     c->hook_post->hookee_post = c;
   if (c->hookee_post)
     c->hookee_post->hook_post = c;
+  if (c->hook_error)
+    c->hook_error->hookee_error = c;
+  if (c->hookee_error)
+    c->hookee_error->hook_error = c;

   if (*list == NULL || strcmp ((*list)->name, name) >= 0)
     {
@@ -294,10 +301,12 @@ add_alias_cmd (const char *name, const char
*oldname, enum command_class theclas

   if (old == 0)
     {
-      struct cmd_list_element *prehook, *prehookee, *posthook, *posthookee;
+      struct cmd_list_element *prehook, *prehookee, *posthook, *posthookee,
+                              *errorhook, *errorhookee;
       struct cmd_list_element *aliases = delete_cmd (name, list,
                              &prehook, &prehookee,
-                             &posthook, &posthookee);
+                             &posthook, &posthookee,
+                             &errorhook, &errorhookee);

       /* If this happens, it means a programmer error somewhere.  */
       gdb_assert (!aliases && !prehook && !prehookee
@@ -778,7 +787,7 @@ add_setshow_zuinteger_cmd (const char *name, enum
command_class theclass,
 /* Remove the command named NAME from the command list.  Return the
    list commands which were aliased to the deleted command.  If the
    command had no aliases, return NULL.  The various *HOOKs are set to
-   the pre- and post-hook commands for the deleted command.  If the
+   the pre-, post- and error-hook commands for the deleted command.  If the
    command does not have a hook, the corresponding out parameter is
    set to NULL.  */

@@ -787,7 +796,9 @@ delete_cmd (const char *name, struct
cmd_list_element **list,
         struct cmd_list_element **prehook,
         struct cmd_list_element **prehookee,
         struct cmd_list_element **posthook,
-        struct cmd_list_element **posthookee)
+        struct cmd_list_element **posthookee,
+        struct cmd_list_element **errorhook,
+        struct cmd_list_element **errorhookee)
 {
   struct cmd_list_element *iter;
   struct cmd_list_element **previous_chain_ptr;
@@ -797,6 +808,8 @@ delete_cmd (const char *name, struct
cmd_list_element **list,
   *prehookee = NULL;
   *posthook = NULL;
   *posthookee = NULL;
+  *errorhook = NULL;
+  *errorhookee = NULL;
   previous_chain_ptr = list;

   for (iter = *previous_chain_ptr; iter; iter = *previous_chain_ptr)
@@ -815,6 +828,10 @@ delete_cmd (const char *name, struct
cmd_list_element **list,
         xfree ((char *) iter->doc);
       *posthook = iter->hook_post;
       *posthookee = iter->hookee_post;
+      if (iter->hookee_error)
+        iter->hookee_error->hook_error = 0;
+      *errorhook = iter->hook_error;
+      *errorhookee = iter->hookee_error;

       /* Update the link.  */
       *previous_chain_ptr = iter->next;
@@ -992,7 +1009,7 @@ help_cmd (const char *command, struct ui_file *stream)
   if (c->func == NULL)
     help_list (cmdlist, "", c->theclass, stream);

-  if (c->hook_pre || c->hook_post)
+  if (c->hook_pre || c->hook_post || c->hook_error)
     fprintf_filtered (stream,
                       "\nThis command has a hook (or hooks) defined:\n");

@@ -1004,6 +1021,10 @@ help_cmd (const char *command, struct ui_file *stream)
     fprintf_filtered (stream,
                       "\tThis command is run before : %s (post hook)\n",
                     c->hook_post->name);
+  if (c->hook_error)
+    fprintf_filtered (stream,
+                  "\tThis command is run before : %s (error hook)\n",
+                c->hook_error->name);
 }

 /*
diff --git a/gdb/cli/cli-decode.h b/gdb/cli/cli-decode.h
index 4ea8063..32ea902 100644
--- a/gdb/cli/cli-decode.h
+++ b/gdb/cli/cli-decode.h
@@ -147,6 +147,9 @@ struct cmd_list_element
     /* Hook for another command to be executed after this command.  */
     struct cmd_list_element *hook_post;

+    /* Hook for another command to be executed if this command fails.  */
+    struct cmd_list_element *hook_error;
+
     /* Nonzero identifies a prefix command.  For them, the address
        of the variable containing the list of subcommands.  */
     struct cmd_list_element **prefixlist;
@@ -209,6 +212,10 @@ struct cmd_list_element
        so the hook can be removed when this one is deleted.  */
     struct cmd_list_element *hookee_post;

+    /* Pointer to command that is hooked by this one, (by hook_error)
+       so the hook can be removed when this one is deleted.  */
+    struct cmd_list_element *hookee_error;
+
     /* Pointer to command that is aliased by this one, so the
        aliased command can be located in case it has been hooked.  */
     struct cmd_list_element *cmd_pointer;
diff --git a/gdb/cli/cli-script.c b/gdb/cli/cli-script.c
index 7302330..9545571 100644
--- a/gdb/cli/cli-script.c
+++ b/gdb/cli/cli-script.c
@@ -337,6 +337,19 @@ execute_cmd_post_hook (struct cmd_list_element *c)
     }
 }

+void
+execute_cmd_error_hook (struct cmd_list_element *c)
+{
+  if ((c->hook_error) && (!c->hook_in))
+    {
+      struct cleanup *cleanups = make_cleanup (clear_hook_in_cleanup, c);
+
+      c->hook_in = 1; /* Prevent recursive hooking.  */
+      execute_user_command (c->hook_error, (char *) 0);
+      do_cleanups (cleanups);
+    }
+}
+
 /* Execute the command in CMD.  */
 static void
 do_restore_user_call_depth (void * call_depth)
@@ -1496,7 +1509,8 @@ define_command (char *comname, int from_tty)
     {
       CMD_NO_HOOK = 0,
       CMD_PRE_HOOK,
-      CMD_POST_HOOK
+      CMD_POST_HOOK,
+      CMD_ERROR_HOOK
     };
   struct command_line *cmds;
   struct cmd_list_element *c, *newc, *hookc = 0, **list;
@@ -1510,6 +1524,8 @@ define_command (char *comname, int from_tty)
 #define    HOOK_LEN 5
 #define HOOK_POST_STRING "hookpost-"
 #define HOOK_POST_LEN    9
+#define HOOK_ERROR_STRING "hookerror-"
+#define HOOK_ERROR_LEN    10

   comfull = comname;
   list = validate_comname (&comname);
@@ -1546,6 +1562,11 @@ define_command (char *comname, int from_tty)
       hook_type      = CMD_POST_HOOK;
       hook_name_size = HOOK_POST_LEN;
     }
+  else if (!strncmp (comname, HOOK_ERROR_STRING, HOOK_ERROR_LEN))
+    {
+      hook_type      = CMD_ERROR_HOOK;
+      hook_name_size = HOOK_ERROR_LEN;
+    }

   if (hook_type != CMD_NO_HOOK)
     {
@@ -1599,6 +1620,11 @@ define_command (char *comname, int from_tty)
           newc->hookee_post = hookc; /* We are marked as hooking
                     target cmd.  */
           break;
+        case CMD_ERROR_HOOK:
+          hookc->hook_error  = newc;  /* Target gets hooked.  */
+          newc->hookee_error = hookc; /* We are marked as hooking
+                    target cmd.  */
+          break;
         default:
           /* Should never come here as hookc would be 0.  */
       internal_error (__FILE__, __LINE__, _("bad switch"));
diff --git a/gdb/command.h b/gdb/command.h
index ab62601..b8771df 100644
--- a/gdb/command.h
+++ b/gdb/command.h
@@ -180,11 +180,12 @@ extern void set_cmd_context (struct cmd_list_element *cmd,
 extern void *get_cmd_context (struct cmd_list_element *cmd);


-/* Execute CMD's pre/post hook.  Throw an error if the command fails.
-   If already executing this pre/post hook, or there is no pre/post
+/* Execute CMD's pre/post/error hook.  Throw an error if the command fails.
+   If already executing this pre/post/error hook, or there is no pre/post/error
    hook, the call is silently ignored.  */
 extern void execute_cmd_pre_hook (struct cmd_list_element *cmd);
 extern void execute_cmd_post_hook (struct cmd_list_element *cmd);
+extern void execute_cmd_error_hook (struct cmd_list_element *cmd);

 /* Return the type of the command.  */
 extern enum cmd_types cmd_type (struct cmd_list_element *cmd);
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 4ec0ec1..c2447db 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -24133,8 +24133,19 @@ pre-execution hooks, for the same command.
 It is valid for a hook to call the command which it hooks.  If this
 occurs, the hook is not re-executed, thereby avoiding infinite recursion.

-@c It would be nice if hookpost could be passed a parameter indicating
-@c if the command it hooks executed properly or not.  FIXME!
+@emph{Note}: The post-execution hook is not run if the command fails; error
+hooks can be used to run code in this case.
+
+@cindex hooks, error-command
+@kindex hookerror
+A hook may be defined which is run after the command you executed if
the command
+fails. Whenever you run the command @samp{foo} and @samp{foo} fails, if the
+user-defined command @samp{hookerror-foo} exists, it is executed (with no
+arguments) after that command.  Error hooks may exist simultaneously with
+pre-execution and post-execution hooks, for the same command.
+
+It is valid for a hook to call the command which it hooks.  If this
+occurs, the hook is not re-executed, thereby avoiding infinite recursion.

 @kindex stop@r{, a pseudo-command}
 In addition, a pseudo-command, @samp{stop} exists.  Defining
@@ -24184,8 +24195,8 @@ not for command aliases; you should define a
hook for the basic command
 name, e.g.@:  @code{backtrace} rather than @code{bt}.
 @c FIXME!  So how does Joe User discover whether a command is an alias
 @c or not?
-You can hook a multi-word command by adding @code{hook-} or
-@code{hookpost-} to the last word of the command, e.g.@:
+You can hook a multi-word command by adding @code{hook-}, @code{hookpost-} or
+@code{hookerror-} to the last word of the command, e.g.@:
 @samp{define target hook-remote} to add a hook to @samp{target remote}.

 If an error occurs during the execution of your hook, execution of
diff --git a/gdb/testsuite/gdb.base/define.exp
b/gdb/testsuite/gdb.base/define.exp
index 8177449..50fd8b3 100644
--- a/gdb/testsuite/gdb.base/define.exp
+++ b/gdb/testsuite/gdb.base/define.exp
@@ -249,8 +249,57 @@ gdb_test_multiple "define target hookpost-testsuite" "" {
     }
 }

+gdb_test_multiple "define target hookerror-testsuite" "" {
+    -re "Type commands for definition of \"target
hookerror-testsuite\".\r\nEnd with a line saying just \"end\".\r\n>$"
{
+    gdb_test "printf \"three\\n\"\nend" "" "define target hookerror-testsuite"
+    }
+}
+
 gdb_test "target testsuite" "one\r\nhello\r\ntwo" "target testsuite with hooks"

+# Test creation of an additional target subcommand that raises an error.
+gdb_test_multiple "define target testsuite-error" "" {
+    -re "Type commands for definition of \"target
testsuite-error\".\r\nEnd with a line saying just \"end\".\r\n>$" {
+    gdb_test "printf \"hello\\n\"\nprint (1/0)\nend" "" "define
target testsuite-error"
+    }
+}
+
+# Add pre-, post- and error-hooks for the testsuite-error target.
+gdb_test_multiple "define target hook-testsuite-error" "" {
+    -re "Type commands for definition of \"target
hook-testsuite-error\".\r\nEnd with a line saying just \"end\".\r\n>$"
{
+    gdb_test "printf \"one\\n\"\nend" "" "define target hook-testsuite-error"
+    }
+}
+
+gdb_test_multiple "define target hookpost-testsuite-error" "" {
+    -re "Type commands for definition of \"target
hookpost-testsuite-error\".\r\nEnd with a line saying just
\"end\".\r\n>$" {
+    gdb_test "printf \"two\\n\"\nend" "" "define target
hookpost-testsuite-error"
+    }
+}
+
+gdb_test_multiple "define target hookerror-testsuite-error" "" {
+    -re "Type commands for definition of \"target
hookerror-testsuite-error\".\r\nEnd with a line saying just
\"end\".\r\n>$" {
+    gdb_test "printf \"three\\n\"\nend" "" "define target
hookerror-testsuite-error"
+    }
+}
+
+gdb_test "target testsuite-error" "one\r\nhello\r\nthree\r\nDivision
by zero" "target testsuite-error with hooks"
+
+# Test creation of an additional target subcommand that raises an
error in its error hook.
+gdb_test_multiple "define target testsuite-errorinhook" "" {
+    -re "Type commands for definition of \"target
testsuite-errorinhook\".\r\nEnd with a line saying just
\"end\".\r\n>$" {
+    gdb_test "printf \"hello\\n\"\nprint (1/0)\nend" "" "define
target testsuite-errorinhook"
+    }
+}
+
+gdb_test_multiple "define target hookerror-testsuite-errorinhook" "" {
+    -re "Type commands for definition of \"target
hookerror-testsuite-errorinhook\".\r\nEnd with a line saying just
\"end\".\r\n>$" {
+    gdb_test "printf \"three\\n\"\nprint (1/0)\nend" "" "define
target hookerror-testsuite-errorinhook"
+    }
+}
+
+gdb_test "target testsuite-errorinhook" "hello\r\nthree\r\nDivision
by zero\r\nDivision by zero" "target testsuite-errorinhook with hooks"
+
 # This is a quasi-define command: Verify that the user can redefine
 # GDB's gdb_prompt.
 #
diff --git a/gdb/top.c b/gdb/top.c
index ed200ba..9535849 100644
--- a/gdb/top.c
+++ b/gdb/top.c
@@ -388,13 +388,27 @@ maybe_wait_sync_command_done (int was_sync)
     wait_sync_command_done ();
 }

+static void
+call_error_hook_cleanup(void* p)
+{
+  TRY
+    {
+      execute_cmd_error_hook (p);
+    }
+  CATCH (ex, RETURN_MASK_ALL)
+    {
+      exception_print (gdb_stderr, ex);
+    }
+  END_CATCH
+}
+
 /* Execute the line P as a command, in the current user context.
    Pass FROM_TTY as second argument to the defining function.  */

 void
 execute_command (char *p, int from_tty)
 {
-  struct cleanup *cleanup_if_error, *cleanup;
+  struct cleanup *cleanup_if_error, *cleanup, *cmd_cleanup;
   struct cmd_list_element *c;
   char *line;

@@ -456,6 +470,7 @@ execute_command (char *p, int from_tty)

       /* If this command has been pre-hooked, run the hook first.  */
       execute_cmd_pre_hook (c);
+      cmd_cleanup = make_cleanup (call_error_hook_cleanup, c);

       if (c->deprecated_warn_user)
     deprecated_cmd_warning (line);
@@ -478,6 +493,7 @@ execute_command (char *p, int from_tty)

       /* If this command has been post-hooked, run the hook last.  */
       execute_cmd_post_hook (c);
+      discard_cleanups (cmd_cleanup);

     }


On Wed, Jan 13, 2016 at 3:21 PM, Stephen Cross <scross@undo-software.com> wrote:
> Sorry for the delay in my response.
>
>> It may happen to work in practice on currently supported hosts,
>> but it's undefined C/C++.  Wrapper is the way to go, just like the
>> comment says.
>
> Thanks for clarifying.
>
>> Do you support debugging with MI?  Or users scripting gdb with Python?
>
> We do support MI and some GDB Python scripting (i.e. that doesn't
> interfere with our own scripting; we've tried to minimise our own
> scripting for this reason).
>
>> Seems to me you'll still end up with problems with e.g., varobjs with
>> function calls, -data-evaluate-expression, etc., which you'd end up
>> solving probably with events around expression evaluation, similar to
>> the infcall ones.
>
> Yes, this is right and that's another part of this that we're working on.
>
>> If you determined that up until recently, gdb used to call the
>> hookpost even on error, and this was a recent regression, then it'd
>> shine a different light on the idea.  OTOH, if this has always been
>> this way, then I'm more inclined to have some way to distinguish
>> normal hookpost vs error.
>
> My testing suggests this behaviour (not calling hookpost on error) has
> been consistent since at least GDB 7.0. So it's not a recent
> regression.
>
> So yes, hookerror-<command> seems like a sensible addition. I'll start
> putting together a patch for this.
>
>> Doesn't have to be literal "hookerror", could be something less
>> confusing if you find it.
>
> I think this is a clear name.
>
>> Hmm, perhaps we should at least print the original error before
>> losing it?
>
> I think this is a problem more generally with GDB's internal
> exceptions, since a new exception overrides the current exception
> being handled (these semantics are similar to throwing from a finally
> block in Java).
>
> I imagine we could force it to print the original error by adding
> another 'print_error_cleanup' that is run when the call to
> 'execute_cmd_post_hook' ends up throwing inside
> 'call_post_hook_cleanup'.
>
> Alternatively, we could have a catch around the
> 'execute_cmd_post_hook' that would print the (new) error that came
> from running the 'hookerror' and then we'd return normally from the
> cleanup so the original error would be processed as normal. If there
> was no original error it would still prevent the 'hookerror' exception
> from leaking out of the cleanup. I think these semantics are possibly
> more intuitive.
>
> Thanks,
> Stephen
>
> On Wed, Dec 9, 2015 at 5:03 PM, Pedro Alves <palves@redhat.com> wrote:
>> On 12/03/2015 04:11 PM, Stephen Cross wrote:
>>> Hi Pedro,
>>>
>>>> Implementation approach, or on the idea in the first place?
>>>
>>> I'm mostly looking for input on the idea, because I know that the
>>> proposed change affects the behaviour of post-hooks.
>>>
>>> The only relevant point about the implementation was that I added:
>>>
>>> +static void
>>> +call_post_hook_cleanup(void* p)
>>> +{
>>> +    execute_cmd_post_hook (p);
>>> +}
>>>
>>> I added this in response to a comment in 'cleanups.h' that says
>>> (emphasis on the last line):
>>>
>>> /* NOTE: cagney/2000-03-04: This typedef is strictly for the
>>>    make_cleanup function declarations below.  Do not use this typedef
>>>    as a cast when passing functions into the make_cleanup() code.
>>>    Instead either use a bounce function or add a wrapper function.
>>>    Calling a f(char*) function with f(void*) is non-portable.  */
>>>
>>> I had thought that calling f(char*) via f(void*) would be portable,
>>> but I've added the wrapper function just in case. What do you think?
>>
>> It may happen to work in practice on currently supported hosts,
>> but it's undefined C/C++.  Wrapper is the way to go, just like the
>> comment says.
>>
>>>
>>>> I think it'd help if you told us the motivation.  What's the intent
>>>> of running the hookpost even on error?  What are you trying to use the
>>>> hooks for?
>>>
>>> Our focus here is on commands that can perform inferior calls. We have
>>> a replacement for gdbserver that by default doesn't support inferior
>>> calls, since we can be part way through a debuggee's history (our core
>>> product is a reversible debugger). So for inferior calls we have to
>>> issue a command to tell our server to fork the current debuggee
>>> process and then GDB can make arbitrary modifications to the fork
>>> child process; once the inferior call is complete we then issue
>>> another command to tell the server to drop the fork child process and
>>> switch back to the parent process.
>>>
>>> We're currently using the inferior call events added by my colleague
>>> (Nick Bull) and these work for most cases. However we've found that if
>>> GDB performs an inferior call which returns a pointer and then prints
>>> that, GDB will access the memory *after* issuing the inferior call end
>>> event. If the inferior call returns a buffer it allocated/modified
>>> then this can cause us to print the old value of the buffer.
>>>
>>> Hooks solve this problem because we can keep the fork child process
>>> around long enough for GDB to read the correct value. Unfortunately
>>> this means that if the 'print' command fails for any reason then we
>>> won't have been notified to drop the child process, affecting the rest
>>> of the debug session.
>>
>> Thanks for the explanation.
>>
>> Do you support debugging with MI?  Or users scripting gdb with Python?
>> Seems to me you'll still end up with problems with e.g., varobjs with
>> function calls, -data-evaluate-expression, etc., which you'd end up
>> solving probably with events around expression evaluation, similar to
>> the infcall ones.
>>
>>>
>>>> Playing devil's advocate, isn't it reasonable to say that existing
>>>> hookpost scripts out there may be assuming that they only run if
>>>> the hooked command finished successfully?
>>>
>>> The online docs say "Whenever you run the command âfooâ, if the
>>> user-defined command âhookpost-fooâ exists, it is executed (with no
>>> arguments) after that command.". They don't seem to mention that
>>> sometimes the post-hook might not be run. Having said that, users may
>>> have observed this happening in practice.
>>
>> If you determined that up until recently, gdb used to call the
>> hookpost even on error, and this was a recent regression, then it'd
>> shine a different light on the idea.  OTOH, if this has always been
>> this way, then I'm more inclined to have some way to distinguish
>> normal hookpost vs error.
>>
>>>
>>>> Wonder whether we should have that.  Alternatively, guess we could have
>>>> a new hookerror hook, that would run on error instead of hookpost.
>>>
>>> Yes, I think having a new 'hookerror' hook would be reasonable. This
>>> would ensure existing users wouldn't be affected, but the naming might
>>> cause confusion, so hookpost would need to be clearly documented as
>>> only being run in the success case. I'm happy to augment the patch to
>>> do this.
>>
>> Doesn't have to be literal "hookerror", could be something less
>> confusing if you find it.
>>
>>>
>>>> What happens / should happen if the hookpost itself throws an error?  Do
>>>> we lose the original hooked-command's error?  Is that OK?
>>>
>>> I previously tested this case with the patch applied and it appears
>>> that the error in the post-hook is what appears. So yes, we do lose
>>> the original hooked command's error. It looks like this is because the
>>> throw_exception() function inside GDB first calls 'do_cleanups
>>> (all_cleanups ());' and do_cleanups() allows cleanup functions to
>>> throw (and it updates the list of cleanups before running each
>>> cleanup).
>>>
>>> This behaviour seems OK to me, particularly if we added a new
>>> 'hookerror' and warned in the documentation that this occurs.
>>> Presumably this should also have a testcase.
>>
>> Hmm, perhaps we should at least print the original error before
>> losing it?
>>
>> Thanks,
>> Pedro Alves
>>
>
>
>
> --
> Stephen Cross
>
> Software Engineer at Undo Software



-- 
Stephen Cross

Software Engineer at Undo Software