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

Christina Schimpe via Gdb-patches
2023-06-01T16:35:20Z

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: 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.
+* set debug breakpoints on|off
+ show debug breakpoints
+ Print additional debug messages about breakpoint insertion and removal.
+
* 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));
+
+ 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)
{
}

+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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