[PATCH v3 0/1] Add breakpoint location debugging logs

[PATCH v3 0/1] Add breakpoint location debugging logs

[Christina Schimpe]

Hi all,

this is my v3 for the patch "gdb, breakpoint: add breakpoint location debugging
logs", which addresses the feedback of Simon.
The documentation part has been approved by Eli.

V2 of this patch can be found here: 
https://sourceware.org/pipermail/gdb-patches/2023-March/197899.html

Changes since V2:
* Comments
* Logging output

Regards,
Christina

Mihails Strasuns (1):
  gdb, breakpoint: add breakpoint location debugging logs

 gdb/NEWS            |  4 +++
 gdb/breakpoint.c    | 73 +++++++++++++++++++++++++++++++++++++++++++++
 gdb/doc/gdb.texinfo |  8 +++++
 3 files changed, 85 insertions(+)

-- 
2.25.1

Intel Deutschland GmbH
Registered Address: Am Campeon 10, 85579 Neubiberg, Germany
Tel: +49 89 99 8853-0, www.intel.de <http://www.intel.de>
Managing Directors: Christin Eisenschmid, Sharon Heck, Tiffany Doon Silva  
Chairperson of the Supervisory Board: Nicole Lau
Registered Office: Munich
Commercial Register: Amtsgericht Muenchen HRB 186928

[PATCH v3 1/1] gdb, breakpoint: add breakpoint location debugging logs

[Christina Schimpe]

From: Mihails Strasuns <mihails.strasuns@intel.com>

Add new commands:

  set debug breakpoints on|off
  show debug breakpoints

This patch introduces new debugging information that prints
breakpoint location insertion and removal flow.

The debug output looks like:
~~~
(gdb) set debug breakpoints on
(gdb) disassemble main
Dump of assembler code for function main:
   0x0000555555555129 <+0>:	endbr64
   0x000055555555512d <+4>:	push   %rbp
   0x000055555555512e <+5>:	mov    %rsp,%rbp
=> 0x0000555555555131 <+8>:	mov    $0x0,%eax
   0x0000555555555136 <+13>:	pop    %rbp
   0x0000555555555137 <+14>:	ret
End of assembler dump.
(gdb) break *0x0000555555555137
Breakpoint 2 at 0x555555555137: file main.c, line 4.
[breakpoints] update_global_location_list: insert_mode = UGLL_MAY_INSERT
(gdb) c
Continuing.
[breakpoints] update_global_location_list: insert_mode = UGLL_INSERT
[breakpoints] insert_bp_location: bp_location (0x55d3881c1e20) at address 0x555555555137 in main at main.c:4
[breakpoints] insert_bp_location: bp_location (0x55d38827d670) at address 0x7ffff7fd37b5
[breakpoints] insert_bp_location: bp_location (0x55d388295880) at address 0x7ffff7fe509e
[breakpoints] insert_bp_location: bp_location (0x55d388295e00) at address 0x7ffff7fe63f4
[breakpoints] remove_breakpoint_1: bp_location (0x55d3881c1e20) due to regular remove at address 0x555555555137 in main at main.c:4
[breakpoints] remove_breakpoint_1: bp_location (0x55d38827d670) due to regular remove at address 0x7ffff7fd37b5
[breakpoints] remove_breakpoint_1: bp_location (0x55d388295880) due to regular remove at address 0x7ffff7fe509e
[breakpoints] remove_breakpoint_1: bp_location (0x55d388295e00) due to regular remove at address 0x7ffff7fe63f4

Breakpoint 2, 0x0000555555555137 in main () at main.c:4
4	}
~~~

Co-Authored-By: Christina Schimpe <christina.schimpe@intel.com>
---
 gdb/NEWS            |  4 +++
 gdb/breakpoint.c    | 73 +++++++++++++++++++++++++++++++++++++++++++++
 gdb/doc/gdb.texinfo |  8 +++++
 3 files changed, 85 insertions(+)

diff --git a/gdb/NEWS b/gdb/NEWS
index cc262f1f8a6..f413cd5aeb4 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -3,6 +3,10 @@
 
 *** Changes since GDB 13
 
+* set debug breakpoints on|off
+  show debug breakpoints
+  Print additional debug messages about breakpoint insertion and removal.
+
 * Removed targets and native configurations
 
   GDB no longer supports AIX 4.x, AIX 5.x and AIX 6.x.  The minimum supported
diff --git a/gdb/breakpoint.c b/gdb/breakpoint.c
index 7228acfd8fe..8db810fd465 100644
--- a/gdb/breakpoint.c
+++ b/gdb/breakpoint.c
@@ -163,6 +163,8 @@ static bool bl_address_is_meaningful (bp_location *loc);
 
 static int find_loc_num_by_location (const bp_location *loc);
 
+static std::string breakpoint_location_to_buffer (bp_location *bl);
+
 /* update_global_location_list's modes of operation wrt to whether to
    insert locations now.  */
 enum ugll_insert_mode
@@ -198,6 +200,24 @@ enum ugll_insert_mode
   UGLL_INSERT
 };
 
+/* Return a textual version of INSERT_MODE.  */
+
+static const char *
+ugll_insert_mode_text (ugll_insert_mode insert_mode)
+{
+  switch (insert_mode)
+    {
+    case UGLL_DONT_INSERT:
+      return "UGLL_DONT_INSERT";
+    case UGLL_MAY_INSERT:
+      return "UGLL_MAY_INSERT";
+    case UGLL_INSERT:
+      return "UGLL_INSERT";
+    }
+
+  gdb_assert_not_reached ("must handle all enum values");
+}
+
 static void update_global_location_list (enum ugll_insert_mode);
 
 static void update_global_location_list_nothrow (enum ugll_insert_mode);
@@ -508,6 +528,22 @@ show_always_inserted_mode (struct ui_file *file, int from_tty,
 	      value);
 }
 
+/* True if breakpoints debug output is enabled.  */
+static bool debug_breakpoints = false;
+
+/* Print a "breakpoints" debug statement.  */
+#define breakpoint_debug_printf(fmt, ...) \
+  debug_prefixed_printf_cond (debug_breakpoints, "breakpoints", fmt, \
+			      ##__VA_ARGS__)
+
+/* "show debug breakpoints" implementation.  */
+static void
+show_debug_breakpoints (struct ui_file *file, int from_tty,
+			struct cmd_list_element *c, const char *value)
+{
+  gdb_printf (file, _("Breakpoint location debugging is %s.\n"), value);
+}
+
 /* See breakpoint.h.  */
 
 int
@@ -2710,6 +2746,11 @@ insert_bp_location (struct bp_location *bl,
   if (!should_be_inserted (bl) || (bl->inserted && !bl->needs_update))
     return 0;
 
+  breakpoint_debug_printf ("bp_location (%s) at address %s %s",
+			    host_address_to_string (bl),
+			    paddress (bl->gdbarch, bl->address),
+			    breakpoint_location_to_buffer (bl).c_str ());
+
   /* Note we don't initialize bl->target_info, as that wipes out
      the breakpoint location's shadow_contents if the breakpoint
      is still inserted at that location.  This in turn breaks
@@ -3264,6 +3305,8 @@ remove_breakpoints_inf (inferior *inf)
 {
   int val;
 
+  breakpoint_debug_printf ("inf->num = %d", inf->num);
+
   for (bp_location *bl : all_bp_locations ())
     {
       if (bl->pspace != inf->pspace)
@@ -3908,6 +3951,13 @@ detach_breakpoints (ptid_t ptid)
 static int
 remove_breakpoint_1 (struct bp_location *bl, enum remove_bp_reason reason)
 {
+  breakpoint_debug_printf ("bp_location (%s) due to %s at address %s %s",
+			   host_address_to_string (bl),
+			   (reason == REMOVE_BREAKPOINT
+			     ? "regular remove" : "detach"),
+			   paddress (bl->gdbarch, bl->address),
+			   breakpoint_location_to_buffer (bl).c_str ());
+
   int val;
 
   /* BL is never in moribund_locations by our callers.  */
@@ -6210,6 +6260,17 @@ print_breakpoint_location (const breakpoint *b,
     }
 }
 
+/* Return the output of the print_breakpoint_location BL as a string.  */
+static std::string
+breakpoint_location_to_buffer (bp_location *bl)
+{
+  string_file stb;
+  current_uiout->redirect (&stb);
+  print_breakpoint_location (bl->owner, bl);
+  current_uiout->redirect (nullptr);
+  return stb.string ();
+}
+
 static const char *
 bptype_string (enum bptype type)
 {
@@ -11147,6 +11208,9 @@ update_global_location_list (enum ugll_insert_mode insert_mode)
   /* Last breakpoint location program space that was marked for update.  */
   int last_pspace_num = -1;
 
+  breakpoint_debug_printf ("insert_mode = %s",
+			   ugll_insert_mode_text (insert_mode));
+
   /* Used in the duplicates detection below.  When iterating over all
      bp_locations, points to the first bp_location of a given address.
      Breakpoints and watchpoints of different types are never
@@ -14880,6 +14944,15 @@ when execution stops."),
 				&breakpoint_set_cmdlist,
 				&breakpoint_show_cmdlist);
 
+  add_setshow_boolean_cmd ("breakpoints", class_maintenance,
+			   &debug_breakpoints, _("\
+Set breakpoint location debugging."), _("\
+Show breakpoint location debugging."), _("\
+When non-zero, breakpoint location specific debugging is enabled."),
+			   NULL,
+			   show_debug_breakpoints,
+			   &setdebuglist, &showdebuglist);
+
   add_setshow_enum_cmd ("condition-evaluation", class_breakpoint,
 			condition_evaluation_enums,
 			&condition_evaluation_mode_1, _("\
diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
index 6c811b8be2e..04e77350da1 100644
--- a/gdb/doc/gdb.texinfo
+++ b/gdb/doc/gdb.texinfo
@@ -28315,6 +28315,14 @@ debugging info.
 Turn on or off debugging messages for built-in XML parsers.
 @item show debug xml
 Displays the current state of XML debugging messages.
+
+@item set debug breakpoints
+@cindex breakpoint debugging info
+Turns on or off display of @value{GDBN} debugging info for breakpoint insertion
+and removal.  The default is off.
+@item show debug breakpoints
+Displays the current state of displaying @value{GDBN} debugging info for
+breakpoint insertion and removal.
 @end table
 
 @node Other Misc Settings
-- 
2.25.1

Intel Deutschland GmbH
Registered Address: Am Campeon 10, 85579 Neubiberg, Germany
Tel: +49 89 99 8853-0, www.intel.de <http://www.intel.de>
Managing Directors: Christin Eisenschmid, Sharon Heck, Tiffany Doon Silva  
Chairperson of the Supervisory Board: Nicole Lau
Registered Office: Munich
Commercial Register: Amtsgericht Muenchen HRB 186928

Re: [PATCH v3 1/1] gdb, breakpoint: add breakpoint location debugging logs

[Andrew Burgess]

Christina Schimpe via Gdb-patches <gdb-patches@sourceware.org> writes:

> From: Mihails Strasuns <mihails.strasuns@intel.com>
>
> Add new commands:
>
>   set debug breakpoints on|off
>   show debug breakpoints
>
> This patch introduces new debugging information that prints
> breakpoint location insertion and removal flow.
>
> The debug output looks like:
> ~~~
> (gdb) set debug breakpoints on
> (gdb) disassemble main
> Dump of assembler code for function main:
>    0x0000555555555129 <+0>:	endbr64
>    0x000055555555512d <+4>:	push   %rbp
>    0x000055555555512e <+5>:	mov    %rsp,%rbp
> => 0x0000555555555131 <+8>:	mov    $0x0,%eax
>    0x0000555555555136 <+13>:	pop    %rbp
>    0x0000555555555137 <+14>:	ret
> End of assembler dump.
> (gdb) break *0x0000555555555137
> Breakpoint 2 at 0x555555555137: file main.c, line 4.
> [breakpoints] update_global_location_list: insert_mode = UGLL_MAY_INSERT
> (gdb) c
> Continuing.
> [breakpoints] update_global_location_list: insert_mode = UGLL_INSERT
> [breakpoints] insert_bp_location: bp_location (0x55d3881c1e20) at address 0x555555555137 in main at main.c:4
> [breakpoints] insert_bp_location: bp_location (0x55d38827d670) at address 0x7ffff7fd37b5
> [breakpoints] insert_bp_location: bp_location (0x55d388295880) at address 0x7ffff7fe509e
> [breakpoints] insert_bp_location: bp_location (0x55d388295e00) at address 0x7ffff7fe63f4
> [breakpoints] remove_breakpoint_1: bp_location (0x55d3881c1e20) due to regular remove at address 0x555555555137 in main at main.c:4
> [breakpoints] remove_breakpoint_1: bp_location (0x55d38827d670) due to regular remove at address 0x7ffff7fd37b5
> [breakpoints] remove_breakpoint_1: bp_location (0x55d388295880) due to regular remove at address 0x7ffff7fe509e
> [breakpoints] remove_breakpoint_1: bp_location (0x55d388295e00) due to regular remove at address 0x7ffff7fe63f4
>
> Breakpoint 2, 0x0000555555555137 in main () at main.c:4
> 4	}
> ~~~
>
> Co-Authored-By: Christina Schimpe <christina.schimpe@intel.com>
> ---
>  gdb/NEWS            |  4 +++
>  gdb/breakpoint.c    | 73 +++++++++++++++++++++++++++++++++++++++++++++
>  gdb/doc/gdb.texinfo |  8 +++++
>  3 files changed, 85 insertions(+)
>
> diff --git a/gdb/NEWS b/gdb/NEWS
> index cc262f1f8a6..f413cd5aeb4 100644
> --- a/gdb/NEWS
> +++ b/gdb/NEWS
> @@ -3,6 +3,10 @@
>  
>  *** Changes since GDB 13
>  
> +* set debug breakpoints on|off
> +  show debug breakpoints
> +  Print additional debug messages about breakpoint insertion and removal.
> +
>  * Removed targets and native configurations
>  
>    GDB no longer supports AIX 4.x, AIX 5.x and AIX 6.x.  The minimum supported
> diff --git a/gdb/breakpoint.c b/gdb/breakpoint.c
> index 7228acfd8fe..8db810fd465 100644
> --- a/gdb/breakpoint.c
> +++ b/gdb/breakpoint.c
> @@ -163,6 +163,8 @@ static bool bl_address_is_meaningful (bp_location *loc);
>  
>  static int find_loc_num_by_location (const bp_location *loc);
>  
> +static std::string breakpoint_location_to_buffer (bp_location *bl);
> +
>  /* update_global_location_list's modes of operation wrt to whether to
>     insert locations now.  */
>  enum ugll_insert_mode
> @@ -198,6 +200,24 @@ enum ugll_insert_mode
>    UGLL_INSERT
>  };
>  
> +/* Return a textual version of INSERT_MODE.  */
> +
> +static const char *
> +ugll_insert_mode_text (ugll_insert_mode insert_mode)
> +{
> +  switch (insert_mode)
> +    {
> +    case UGLL_DONT_INSERT:
> +      return "UGLL_DONT_INSERT";
> +    case UGLL_MAY_INSERT:
> +      return "UGLL_MAY_INSERT";
> +    case UGLL_INSERT:
> +      return "UGLL_INSERT";
> +    }
> +
> +  gdb_assert_not_reached ("must handle all enum values");
> +}
> +
>  static void update_global_location_list (enum ugll_insert_mode);
>  
>  static void update_global_location_list_nothrow (enum ugll_insert_mode);
> @@ -508,6 +528,22 @@ show_always_inserted_mode (struct ui_file *file, int from_tty,
>  	      value);
>  }
>  
> +/* True if breakpoints debug output is enabled.  */
> +static bool debug_breakpoints = false;
> +
> +/* Print a "breakpoints" debug statement.  */
> +#define breakpoint_debug_printf(fmt, ...) \
> +  debug_prefixed_printf_cond (debug_breakpoints, "breakpoints", fmt, \
> +			      ##__VA_ARGS__)
> +
> +/* "show debug breakpoints" implementation.  */
> +static void
> +show_debug_breakpoints (struct ui_file *file, int from_tty,
> +			struct cmd_list_element *c, const char *value)
> +{
> +  gdb_printf (file, _("Breakpoint location debugging is %s.\n"), value);
> +}
> +
>  /* See breakpoint.h.  */
>  
>  int
> @@ -2710,6 +2746,11 @@ insert_bp_location (struct bp_location *bl,
>    if (!should_be_inserted (bl) || (bl->inserted && !bl->needs_update))
>      return 0;
>  
> +  breakpoint_debug_printf ("bp_location (%s) at address %s %s",
> +			    host_address_to_string (bl),
> +			    paddress (bl->gdbarch, bl->address),
> +			    breakpoint_location_to_buffer (bl).c_str ());

Here, and again later on, I think it might be nice to include the actual
number of the owning breakpoint, something like:

  "Breakpoint %d, location (%s) at address %s ...."

this might make it easier to identify which breakpoint is being worked
on?

I wonder if it's worth having a small helper function to create this
whole thing in a std::string as it might be used in many breakpoint
related debug lines?

> +
>    /* Note we don't initialize bl->target_info, as that wipes out
>       the breakpoint location's shadow_contents if the breakpoint
>       is still inserted at that location.  This in turn breaks
> @@ -3264,6 +3305,8 @@ remove_breakpoints_inf (inferior *inf)
>  {
>    int val;
>  
> +  breakpoint_debug_printf ("inf->num = %d", inf->num);
> +
>    for (bp_location *bl : all_bp_locations ())
>      {
>        if (bl->pspace != inf->pspace)
> @@ -3908,6 +3951,13 @@ detach_breakpoints (ptid_t ptid)
>  static int
>  remove_breakpoint_1 (struct bp_location *bl, enum remove_bp_reason reason)
>  {
> +  breakpoint_debug_printf ("bp_location (%s) due to %s at address %s %s",
> +			   host_address_to_string (bl),
> +			   (reason == REMOVE_BREAKPOINT
> +			     ? "regular remove" : "detach"),
> +			   paddress (bl->gdbarch, bl->address),
> +			   breakpoint_location_to_buffer (bl).c_str ());
> +
>    int val;
>  
>    /* BL is never in moribund_locations by our callers.  */
> @@ -6210,6 +6260,17 @@ print_breakpoint_location (const breakpoint *b,
>      }
>  }
>  
> +/* Return the output of the print_breakpoint_location BL as a string.  */
> +static std::string
> +breakpoint_location_to_buffer (bp_location *bl)
> +{
> +  string_file stb;
> +  current_uiout->redirect (&stb);
> +  print_breakpoint_location (bl->owner, bl);
> +  current_uiout->redirect (nullptr);
> +  return stb.string ();
> +}

I think this would be better implemented as a "to_string" method on the
bp_location class.

Also, instead of calling ui_out::redirect directly, you should be using
ui_out_redirect_pop.  See save_breakpoints for an example of this in
use.


> +
>  static const char *
>  bptype_string (enum bptype type)
>  {
> @@ -11147,6 +11208,9 @@ update_global_location_list (enum ugll_insert_mode insert_mode)
>    /* Last breakpoint location program space that was marked for update.  */
>    int last_pspace_num = -1;
>  
> +  breakpoint_debug_printf ("insert_mode = %s",
> +			   ugll_insert_mode_text (insert_mode));
> +
>    /* Used in the duplicates detection below.  When iterating over all
>       bp_locations, points to the first bp_location of a given address.
>       Breakpoints and watchpoints of different types are never
> @@ -14880,6 +14944,15 @@ when execution stops."),
>  				&breakpoint_set_cmdlist,
>  				&breakpoint_show_cmdlist);
>  
> +  add_setshow_boolean_cmd ("breakpoints", class_maintenance,
> +			   &debug_breakpoints, _("\
> +Set breakpoint location debugging."), _("\
> +Show breakpoint location debugging."), _("\
> +When non-zero, breakpoint location specific debugging is enabled."),

s/non-zero/on/.

Thanks,
Andrew

> +			   NULL,
> +			   show_debug_breakpoints,
> +			   &setdebuglist, &showdebuglist);
> +
>    add_setshow_enum_cmd ("condition-evaluation", class_breakpoint,
>  			condition_evaluation_enums,
>  			&condition_evaluation_mode_1, _("\
> diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
> index 6c811b8be2e..04e77350da1 100644
> --- a/gdb/doc/gdb.texinfo
> +++ b/gdb/doc/gdb.texinfo
> @@ -28315,6 +28315,14 @@ debugging info.
>  Turn on or off debugging messages for built-in XML parsers.
>  @item show debug xml
>  Displays the current state of XML debugging messages.
> +
> +@item set debug breakpoints
> +@cindex breakpoint debugging info
> +Turns on or off display of @value{GDBN} debugging info for breakpoint insertion
> +and removal.  The default is off.
> +@item show debug breakpoints
> +Displays the current state of displaying @value{GDBN} debugging info for
> +breakpoint insertion and removal.
>  @end table
>  
>  @node Other Misc Settings
> -- 
> 2.25.1
>
> Intel Deutschland GmbH
> Registered Address: Am Campeon 10, 85579 Neubiberg, Germany
> Tel: +49 89 99 8853-0, www.intel.de <http://www.intel.de>
> Managing Directors: Christin Eisenschmid, Sharon Heck, Tiffany Doon Silva  
> Chairperson of the Supervisory Board: Nicole Lau
> Registered Office: Munich
> Commercial Register: Amtsgericht Muenchen HRB 186928

Re: [PATCH v3 1/1] gdb, breakpoint: add breakpoint location debugging logs

[Simon Marchi]

> @@ -3908,6 +3951,13 @@ detach_breakpoints (ptid_t ptid)
>  static int
>  remove_breakpoint_1 (struct bp_location *bl, enum remove_bp_reason reason)
>  {
> +  breakpoint_debug_printf ("bp_location (%s) due to %s at address %s %s",
> +			   host_address_to_string (bl),
> +			   (reason == REMOVE_BREAKPOINT
> +			     ? "regular remove" : "detach"),
Another little nit: for consistency, let's add a remove_bp_reason_str
function to convert an enum remove_bp_reason to a string (same as you
did for ugll_insert_mode).  This way we'll get an assertion failure if
we add a new enumerator and for got to handle it in the switch.

And for all functions of this kind, I would be tempted to use
DIAGNOSTIC_ERROR_SWITCH, like we have in the target_waitkind_str), so
that compilers that support it can warn if we miss an enumerator in the
switch.

Simon

RE: [PATCH v3 1/1] gdb, breakpoint: add breakpoint location debugging logs

[Schimpe, Christina]

Hi Andrew,

thanks a lot for your review and I am sorry for getting back to this so late.
I agree with all of your feedback and will post a v4 soon.

Christina 
Intel Deutschland GmbH
Registered Address: Am Campeon 10, 85579 Neubiberg, Germany
Tel: +49 89 99 8853-0, www.intel.de <http://www.intel.de>
Managing Directors: Christin Eisenschmid, Sharon Heck, Tiffany Doon Silva  
Chairperson of the Supervisory Board: Nicole Lau
Registered Office: Munich
Commercial Register: Amtsgericht Muenchen HRB 186928

RE: [PATCH v3 1/1] gdb, breakpoint: add breakpoint location debugging logs

[Schimpe, Christina]

Hi Simon, 

Thanks a lot for your review.

> Another little nit: for consistency, let's add a remove_bp_reason_str function to
> convert an enum remove_bp_reason to a string (same as you did for
> ugll_insert_mode).  This way we'll get an assertion failure if we add a new
> enumerator and for got to handle it in the switch.
> 
> And for all functions of this kind, I would be tempted to use
> DIAGNOSTIC_ERROR_SWITCH, like we have in the target_waitkind_str), so that
> compilers that support it can warn if we miss an enumerator in the switch.


Your comments make sense to me, I will post a v4 soon.

Christina
Intel Deutschland GmbH
Registered Address: Am Campeon 10, 85579 Neubiberg, Germany
Tel: +49 89 99 8853-0, www.intel.de <http://www.intel.de>
Managing Directors: Christin Eisenschmid, Sharon Heck, Tiffany Doon Silva  
Chairperson of the Supervisory Board: Nicole Lau
Registered Office: Munich
Commercial Register: Amtsgericht Muenchen HRB 186928