gdb: don't always print breakpoint location after failed condition check

Consider the following session:

  (gdb) list some_func
  1	int
  2	some_func ()
  3	{
  4	  int *p = 0;
  5	  return *p;
  6	}
  7
  8	void
  9	foo ()
  10	{
  (gdb) break foo if (some_func ())
  Breakpoint 1 at 0x40111e: file bpcond.c, line 11.
  (gdb) r
  Starting program: /tmp/bpcond

  Program received signal SIGSEGV, Segmentation fault.
  0x0000000000401116 in some_func () at bpcond.c:5
  5	  return *p;
  Error in testing condition for breakpoint 1:
  The program being debugged stopped while in a function called from GDB.
  Evaluation of the expression containing the function
  (some_func) will be abandoned.
  When the function is done executing, GDB will silently stop.

  Breakpoint 1, 0x0000000000401116 in some_func () at bpcond.c:5
  5	  return *p;
  (gdb)

What happens here is the breakpoint condition includes a call to an
inferior function, and the inferior function segfaults.  We can see
that GDB reports the segfault, and then gives an error message that
indicates that an inferior function call was interrupted.

After this GDB appears to report that it is stopped at Breakpoint 1,
inside some_func.

I find this second stop report a little confusing.  While it is true
that GDB stopped as a result of hitting breakpoint 1, I think the
message GDB currently prints might give the impression that GDB is
actually stopped at a location of breakpoint 1, which is not the case.

Also, I find the second stop message draws attention away from
the "Program received signal SIGSEGV, Segmentation fault" stop
message, and this second stop might be thought of as replacing in
someway the earlier message.

In short, I think things would be clearer if the second stop message
were not reported at all, so the output should, I think, look like
this:

  (gdb) list some_func
  1	int
  2	some_func ()
  3	{
  4	  int *p = 0;
  5	  return *p;
  6	}
  7
  8	void
  9	foo ()
  10	{
  (gdb) break foo if (some_func ())
  Breakpoint 1 at 0x40111e: file bpcond.c, line 11.
  (gdb) r
  Starting program: /tmp/bpcond

  Program received signal SIGSEGV, Segmentation fault.
  0x0000000000401116 in some_func () at bpcond.c:5
  5	  return *p;
  Error in testing condition for breakpoint 1:
  The program being debugged stopped while in a function called from GDB.
  Evaluation of the expression containing the function
  (some_func) will be abandoned.
  When the function is done executing, GDB will silently stop.
  (gdb)

The user can still find the number of the breakpoint that triggered
the initial stop in this line:

  Error in testing condition for breakpoint 1:

But there's now only one stop reason reported, the SIGSEGV, which I
think is much clearer.

To achieve this change I set the bpstat::print field when:

  (a) a breakpoint condition evaluation failed, and

  (b) the $pc of the thread changed during condition evaluation.

I've updated the existing tests that checked the error message printed
when a breakpoint condition evaluation failed.

diff --git a/gdb/breakpoint.c b/gdb/breakpoint.c
index ef5e3f4570c592a849ae9c06ec328ab657035344..ebe97940f54c59d9d31745cf17145a5a31dc9671 100644 (file)
--- a/gdb/breakpoint.c
+++ b/gdb/breakpoint.c
@@ -5534,6 +5534,7 @@ bpstat_check_breakpoint_conditions (bpstat *bs, thread_info *thread)
          else
            within_current_scope = false;
        }
+      CORE_ADDR pc_before_check = get_frame_pc (get_selected_frame (nullptr));
       if (within_current_scope)
        {
          try
@@ -5545,6 +5546,17 @@ bpstat_check_breakpoint_conditions (bpstat *bs, thread_info *thread)
              exception_fprintf (gdb_stderr, ex,
                                 "Error in testing condition for breakpoint %d:\n",
                                 b->number);
+
+             /* If the pc value changed as a result of evaluating the
+                condition then we probably stopped within an inferior
+                function call due to some unexpected stop, e.g. the thread
+                hit another breakpoint, or the thread received an
+                unexpected signal.  In this case we don't want to also
+                print the information about this breakpoint.  */
+             CORE_ADDR pc_after_check
+               = get_frame_pc (get_selected_frame (nullptr));
+             if (pc_before_check != pc_after_check)
+               bs->print = 0;
            }
        }
       else

diff --git a/gdb/testsuite/gdb.base/infcall-failure.exp b/gdb/testsuite/gdb.base/infcall-failure.exp
index 214a64f8de3b5176dd2d3b0e6e3dc2cee1f3054d..5ad179a089d5715763c2f60d4505bd3d08eaee54 100644 (file)
--- a/gdb/testsuite/gdb.base/infcall-failure.exp
+++ b/gdb/testsuite/gdb.base/infcall-failure.exp
@@ -78,10 +78,7 @@ proc_with_prefix run_cond_hits_breakpoint_test { async_p non_stop_p } {
             "The program being debugged stopped while in a function called from GDB\\." \
             "Evaluation of the expression containing the function" \
             "\\(func_bp\\) will be abandoned\\." \
-            "When the function is done executing, GDB will silently stop\\." \
-            "" \
-            "Breakpoint ${bp_1_num}, \[^\r\n\]+" \
-            "${::decimal}\\s+\[^\r\n\]+Second breakpoint\[^\r\n\]+"]
+            "When the function is done executing, GDB will silently stop\\."]
 }
 
 # Start GDB according to ASYNC_P and NON_STOP_P, then call an inferior
@@ -138,13 +135,12 @@ proc_with_prefix run_cond_hits_segfault_test { async_p non_stop_p } {
             "${::hex} in func_segfault \\(\\) at \[^\r\n\]+:${::segv_line}" \
             "${::decimal}\\s+\[^\r\n\]+Segfault here\[^\r\n\]+" \
             "Error in testing condition for breakpoint ${bp_1_num}:" \
-            "The program being debugged stopped while in a function called from GDB\\." \
+            "The program being debugged was signaled while in a function called from GDB\\." \
+            "GDB remains in the frame where the signal was received\\." \
+            "To change this behavior use \"set unwindonsignal on\"\\." \
             "Evaluation of the expression containing the function" \
             "\\(func_segfault\\) will be abandoned\\." \
-            "When the function is done executing, GDB will silently stop\\." \
-            "" \
-            "Breakpoint ${bp_1_num}, \[^\r\n\]+" \
-            "${::decimal}\\s+\[^\r\n\]+Segfault here\[^\r\n\]+"]
+            "When the function is done executing, GDB will silently stop\\."]
 }
 
 # Start GDB according to ASYNC_P and NON_STOP_P, then call an inferior
@@ -168,7 +164,9 @@ proc_with_prefix run_call_hits_segfault_test { async_p non_stop_p } {
             "Program received signal SIGSEGV, Segmentation fault\\." \
             "${::hex} in func_segfault \\(\\) at \[^\r\n\]+:${::segv_line}" \
             "${::decimal}\\s+\[^\r\n\]+Segfault here\[^\r\n\]+" \
-            "The program being debugged stopped while in a function called from GDB\\." \
+            "The program being debugged was signaled while in a function called from GDB\\." \
+            "GDB remains in the frame where the signal was received\\." \
+            "To change this behavior use \"set unwindonsignal on\"\\." \
             "Evaluation of the expression containing the function" \
             "\\(func_segfault\\) will be abandoned\\." \
             "When the function is done executing, GDB will silently stop\\."]