Re: [PATCH v4 1/1] gdb, breakpoint: add breakpoint location debugging logs

Andrew Burgess via Gdb-patches
2023-06-07T08:46:12Z

Christina Schimpe <christina.schimpe@intel.com> writes:

> From: Mihails Strasuns <mihails.strasuns@intel.com>
>
> Add new commands:
>
> set debug breakpoints on|off
> show debug breakpoints

I'd like to suggest (but don't require) that we drop the 's' here, so
breakpoints -> breakpoint.

I'd point to other debug settings like frame (not frames), expression
(not expressions), and target (not targets) for precedent. However
there is also threads (not thread) which is why I don't think it would
be fair to require this change -- it's up to you.

>
> 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: Breakpoint 2, location (0x5572b98a6db0) at address 0x555555555137 in main at main.c:4
> [breakpoints] insert_bp_location: Breakpoint -2, location (0x5572b961d450) at address 0x7ffff7fd37b5
> [breakpoints] insert_bp_location: Breakpoint -5, location (0x5572b9634680) at address 0x7ffff7fe509e
> [breakpoints] insert_bp_location: Breakpoint -7, location (0x5572b9634a00) at address 0x7ffff7fe63f4
> [breakpoints] remove_breakpoint_1: Breakpoint 2, location (0x5572b98a6db0) at address 0x555555555137 in main at main.c:4 due to regular remove
> [breakpoints] remove_breakpoint_1: Breakpoint -2, location (0x5572b961d450) at address 0x7ffff7fd37b5 due to regular remove
> [breakpoints] remove_breakpoint_1: Breakpoint -5, location (0x5572b9634680) at address 0x7ffff7fe509e due to regular remove
> [breakpoints] remove_breakpoint_1: Breakpoint -7, location (0x5572b9634a00) at address 0x7ffff7fe63f4 due to regular remove
>
> Breakpoint 2, 0x0000555555555137 in main () at main.c:4
> 4 }
> ~~~
>
> Co-Authored-By: Christina Schimpe <christina.schimpe@intel.com>
> ---
> gdb/NEWS | 5 +++
> gdb/breakpoint.c | 107 ++++++++++++++++++++++++++++++++++++++++++++
> gdb/breakpoint.h | 4 ++
> gdb/doc/gdb.texinfo | 8 ++++
> 4 files changed, 124 insertions(+)
>
> diff --git a/gdb/NEWS b/gdb/NEWS
> index 649a3a9824a..c66fde54e85 100644
> --- a/gdb/NEWS
> +++ b/gdb/NEWS
> @@ -3,6 +3,11 @@
>
> *** Changes since GDB 13
>
> +* GDB now has some support for integer types larger than 64 bits.

I think this line was not intended to be part of this commit.

> +* set debug breakpoints on|off
> + show debug breakpoints
> + Print additional debug messages about breakpoint insertion and removal.

I think this should be moved into the '* New commands' section of the
NEWS file, see for example, how and where 'set always-read-ctf on|off'
is documented in this file.

> +
> * The AArch64 'org.gnu.gdb.aarch64.pauth' Pointer Authentication feature string
> has been deprecated in favor of the 'org.gnu.gdb.aarch64.pauth_v2' feature
> string.
> diff --git a/gdb/breakpoint.c b/gdb/breakpoint.c
> index 0a520cfc169..dd8fac2f1ba 100644
> --- a/gdb/breakpoint.c
> +++ b/gdb/breakpoint.c
> @@ -83,6 +83,7 @@
> #include "progspace-and-thread.h"
> #include "gdbsupport/array-view.h"
> #include "gdbsupport/gdb_optional.h"
> +#include "gdbsupport/common-utils.h"
>
> /* Prototypes for local functions. */
>
> @@ -200,6 +201,68 @@ 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)
> +{
> +/* Make sure the compiler warns if a new ugll_insert_mode enumerator is added
> + but not handled here. */
> +DIAGNOSTIC_PUSH
> +DIAGNOSTIC_ERROR_SWITCH
> + 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";
> + }
> +DIAGNOSTIC_POP
> +
> + gdb_assert_not_reached ("must handle all enum values");
> +}
> +
> +/* Return a textual version of REASON. */
> +
> +static const char *
> +remove_bp_reason_str (remove_bp_reason reason)
> +{
> +/* Make sure the compiler warns if a new remove_bp_reason enumerator is added
> + but not handled here. */
> +DIAGNOSTIC_PUSH
> +DIAGNOSTIC_ERROR_SWITCH
> + switch (reason)
> + {
> + case REMOVE_BREAKPOINT:
> + return "regular remove";
> + case DETACH_BREAKPOINT:
> + return "detach";
> + }
> +DIAGNOSTIC_POP
> +
> + gdb_assert_not_reached ("must handle all enum values");
> +}
> +
> +/* Return a textual version of breakpoint BL describing number, location and
> + address. */
> +
> +static std::string
> +breakpoint_location_address_str (const bp_location* bl)
> +{
> + std::string str = string_printf ("Breakpoint %d, location (%s) at address %s",
> + bl->owner->number,
> + host_address_to_string (bl),
> + paddress (bl->gdbarch, bl->address));

I can't help but think using 'location' in this string is a bad idea,
'location' already has a meaning for GDB breakpoints. How about just
dropping the work 'location'?

> +
> + std::string loc_string = bl->to_string ();
> + if (!loc_string.empty ())
> + str += string_printf (" %s", loc_string.c_str ());
> +
> + return str;
> +}
> +
> static void update_global_location_list (enum ugll_insert_mode);
>
> static void update_global_location_list_nothrow (enum ugll_insert_mode);
> @@ -510,6 +573,22 @@ 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
> @@ -2728,6 +2807,8 @@ insert_bp_location (struct bp_location *bl,
> if (!should_be_inserted (bl) || (bl->inserted && !bl->needs_update))
> return 0;
>
> + breakpoint_debug_printf ("%s", breakpoint_location_address_str (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 +3351,8 @@ 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)
> @@ -3914,6 +3997,10 @@ detach_breakpoints (ptid_t ptid)
> static int
> remove_breakpoint_1 (struct bp_location *bl, enum remove_bp_reason reason)
> {
> + breakpoint_debug_printf ("%s due to %s",
> + breakpoint_location_address_str (bl).c_str (),
> + remove_bp_reason_str (reason));
> +
> int val;
>
> /* BL is never in moribund_locations by our callers. */
> @@ -7424,6 +7511,14 @@ bp_location::bp_location (breakpoint *owner)
> {
> }
>

Missing a comment '/* See breakpoint.h. */'.

Thanks,
Andrew

> +std::string bp_location::to_string () const
> +{
> + string_file stb;
> + ui_out_redirect_pop redir (current_uiout, &stb);
> + print_breakpoint_location (this->owner, this);
> + return stb.string ();
> +}
> +
> /* Decrement reference count. If the reference count reaches 0,
> destroy the bp_location. Sets *BLP to NULL. */
>
> @@ -11157,6 +11252,9 @@ 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
> @@ -14899,6 +14997,15 @@ 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 on, 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/breakpoint.h b/gdb/breakpoint.h
> index da150585f73..f4896293bb7 100644
> --- a/gdb/breakpoint.h
> +++ b/gdb/breakpoint.h
> @@ -509,6 +509,10 @@ class bp_location : public refcounted_object, public intrusive_list_node<bp_loca
>
> /* The objfile the symbol or minimal symbol were found in. */
> const struct objfile *objfile = NULL;
> +
> + /* Return a string representation of the bp_location.
> + This is only meant to be used in debug messages. */
> + std::string to_string () const;
> };
>
> /* A policy class for bp_location reference counting. */
> diff --git a/gdb/doc/gdb.texinfo b/gdb/doc/gdb.texinfo
> index fc55c4e7b43..8c91ecab209 100644
> --- a/gdb/doc/gdb.texinfo
> +++ b/gdb/doc/gdb.texinfo
> @@ -28356,6 +28356,14 @@ 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
>
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