[PATCH v5 1/1] gdb, breakpoint: add breakpoint location debugging logs

[Christina Schimpe <christina.schimpe@intel.com>]

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

Add new commands:

  set debug breakpoint on|off
  show debug breakpoint

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

The debug output looks like:
~~~
(gdb) set debug breakpoint 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.
[breakpoint] update_global_location_list: insert_mode = UGLL_MAY_INSERT
(gdb) c
Continuing.
[breakpoint] update_global_location_list: insert_mode = UGLL_INSERT
[breakpoint] insert_bp_location: Breakpoint 2 (0x5565daddb1e0) at address 0x555555555137 in main at main.c:4
[breakpoint] insert_bp_location: Breakpoint -2 (0x5565dab51c10) at address 0x7ffff7fd37b5
[breakpoint] insert_bp_location: Breakpoint -5 (0x5565dab68f30) at address 0x7ffff7fe509e
[breakpoint] insert_bp_location: Breakpoint -7 (0x5565dab694f0) at address 0x7ffff7fe63f4
[breakpoint] remove_breakpoint_1: Breakpoint 2 (0x5565daddb1e0) at address 0x555555555137 in main at main.c:4 due to regular remove
[breakpoint] remove_breakpoint_1: Breakpoint -2 (0x5565dab51c10) at address 0x7ffff7fd37b5 due to regular remove
[breakpoint] remove_breakpoint_1: Breakpoint -5 (0x5565dab68f30) at address 0x7ffff7fe509e due to regular remove
[breakpoint] remove_breakpoint_1: Breakpoint -7 (0x5565dab694f0) 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            |   4 ++
 gdb/breakpoint.c    | 109 ++++++++++++++++++++++++++++++++++++++++++++
 gdb/breakpoint.h    |   4 ++
 gdb/doc/gdb.texinfo |   8 ++++
 4 files changed, 125 insertions(+)

diff --git a/gdb/NEWS b/gdb/NEWS
index 649a3a9824a..2aafe103dab 100644
--- a/gdb/NEWS
+++ b/gdb/NEWS
@@ -80,6 +80,10 @@
 
 * New commands
 
+set debug breakpoint on|off
+  show debug breakpoint
+  Print additional debug messages about breakpoint insertion and removal.
+
 maintenance print record-instruction [ N ]
   Print the recorded information for a given instruction.  If N is not given
   prints how GDB would undo the last instruction executed.  If N is negative,
diff --git a/gdb/breakpoint.c b/gdb/breakpoint.c
index da6c8de9d14..dc502df9d79 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 (%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 breakpoint debug output is enabled.  */
+static bool debug_breakpoint = false;
+
+/* Print a "breakpoint" debug statement.  */
+#define breakpoint_debug_printf(fmt, ...) \
+  debug_prefixed_printf_cond (debug_breakpoint, "breakpoint", fmt, \
+			      ##__VA_ARGS__)
+
+/* "show debug breakpoint" implementation.  */
+static void
+show_debug_breakpoint (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 +7511,16 @@ bp_location::bp_location (breakpoint *owner)
 {
 }
 
+/* See breakpoint.h.  */
+
+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 +11254,9 @@ 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 +14999,15 @@ when execution stops."),
 				&breakpoint_set_cmdlist,
 				&breakpoint_show_cmdlist);
 
+  add_setshow_boolean_cmd ("breakpoint", class_maintenance,
+			   &debug_breakpoint, _("\
+Set breakpoint location debugging."), _("\
+Show breakpoint location debugging."), _("\
+When on, breakpoint location specific debugging is enabled."),
+			   NULL,
+			   show_debug_breakpoint,
+			   &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 40d1f244417..ce0444c3c02 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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