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

[Bruno Larsen <blarsen@redhat.com>]

On 21/02/2023 10:05, Christina Schimpe via Gdb-patches wrote:
> 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: UGLL_MAY_INSERT
> (gdb) c
> Continuing.
> [breakpoints] update_global_location_list: UGLL_INSERT
> [breakpoints] insert_bp_location: bp_location (0x562881637fb0) at address 0x555555555137 in main at main.c:4
> [breakpoints] insert_bp_location: bp_location (0x56288179a4f0) at address 0x7ffff7fd37b5 <dl_main+8661>
> [breakpoints] insert_bp_location: bp_location (0x56288179ea60) at address 0x7ffff7fe509e <dl_open_worker+1150>
> [breakpoints] insert_bp_location: bp_location (0x5628817184d0) at address 0x7ffff7fe63f4 <_dl_close_worker+2356>
> [breakpoints] remove_breakpoint_1: bp_location (0x562881637fb0) due to regular remove at address 0x555555555137 in main at main.c:4
> [breakpoints] remove_breakpoint_1: bp_location (0x56288179a4f0) due to regular remove at address 0x7ffff7fd37b5 <dl_main+8661>
> [breakpoints] remove_breakpoint_1: bp_location (0x56288179ea60) due to regular remove at address 0x7ffff7fe509e <dl_open_worker+1150>
> [breakpoints] remove_breakpoint_1: bp_location (0x5628817184d0) due to regular remove at address 0x7ffff7fe63f4 <_dl_close_worker+2356>
>
> Breakpoint 2, 0x0000555555555137 in main () at main.c:4
> 4	}
> ~~~
>
> Co-Authored-By: Christina Schimpe <christina.schimpe@intel.com>

Other than a small nit, this looks ok to me, Reviewed-By: Bruno Larsen 
<blarsen@redhat.com>

(please note that the rb tag is not enough for pushing).

> ---
>   gdb/NEWS            |  4 +++
>   gdb/breakpoint.c    | 66 +++++++++++++++++++++++++++++++++++++++++++++
>   gdb/doc/gdb.texinfo |  8 ++++++
>   3 files changed, 78 insertions(+)
>
> diff --git a/gdb/NEWS b/gdb/NEWS
> index 75cd11b204e..f64e0a68c85 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.
> +
>   * Multi-target feature configuration
>   
>     GDB now supports the individual configuration of remote targets' feature
> diff --git a/gdb/breakpoint.c b/gdb/breakpoint.c
> index 0db3adaf916..1c8a05c6cbd 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 +200,22 @@ enum ugll_insert_mode
>     UGLL_INSERT
>   };
>   
> +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 +526,19 @@ show_always_inserted_mode (struct ui_file *file, int from_tty,
>   	      value);
>   }
>   
> +static bool debug_breakpoints = 0;

s/0/false.

-- 
Cheers,
Bruno

> +
> +#define breakpoint_debug_printf(fmt, ...) \
> +  debug_prefixed_printf_cond (debug_breakpoints, "breakpoints",fmt,\
> +			      ##__VA_ARGS__)
> +
> +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 +2741,11 @@ 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
> @@ -3270,6 +3306,8 @@ remove_breakpoints_inf (inferior *inf)
>   {
>     int val;
>   
> +  breakpoint_debug_printf ("remove_breakpoints_inf (%d)", inf->num);
> +
>     for (bp_location *bl : all_bp_locations ())
>       {
>         if (bl->pspace != inf->pspace)
> @@ -3914,6 +3952,13 @@ 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.  */
> @@ -6216,6 +6261,16 @@ print_breakpoint_location (const breakpoint *b,
>       }
>   }
>   
> +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)
>   {
> @@ -11146,6 +11201,8 @@ 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 ("%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
> @@ -14876,6 +14933,15 @@ 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 2a2077c29d1..cf33bd351b1 100644
> --- a/gdb/doc/gdb.texinfo
> +++ b/gdb/doc/gdb.texinfo
> @@ -28272,6 +28272,14 @@ 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