Watchpoint followed by catchpoint misreports watchpoint (PR gdb/28621)

If GDB reports a watchpoint hit, and then the next event is not
TARGET_WAITKIND_STOPPED, but instead some event for which there's a
catchpoint, such that GDB calls bpstat_stop_status, GDB mistakenly
thinks the watchpoint triggered.  Vis, using foll-fork.c:

  (gdb) awatch v
  Hardware access (read/write) watchpoint 2: v
  (gdb) catch fork
  Catchpoint 3 (fork)
  (gdb) c
  Continuing.

  Hardware access (read/write) watchpoint 2: v

  Old value = 0
  New value = 5
  main () at gdb.base/foll-fork.c:16
  16        pid = fork ();
  (gdb)
  Continuing.

  Hardware access (read/write) watchpoint 2: v      <<<<
                                                    <<<< these lines are spurious
  Value = 5                                         <<<<

  Catchpoint 3 (forked process 1712369), arch_fork (ctid=0x7ffff7fa4810) at arch-fork.h:49
  49      arch-fork.h: No such file or directory.
  (gdb)

The problem is that when we handle the fork event, nothing called
watchpoints_triggered before calling bpstat_stop_status.  Thus, each
watchpoint's watchpoint_triggered field was still set to
watch_triggered_yes from the previous (real) watchpoint stop.
watchpoint_triggered is only current called in the handle_signal_stop
path, when handling TARGET_WAITKIND_STOPPED.

This fixes it by adding watchpoint_triggered calls in the other events
paths that call bpstat_stop_status.  But instead of adding them
explicitly, it adds a new function bpstat_stop_status_nowatch that
wraps bpstat_stop_status and calls watchpoint_triggered, and then
replaces most calls to bpstat_stop_status with calls to
bpstat_stop_status_nowatch.

This required constifying watchpoints_triggered.

New test included, which fails without the fix.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=28621

Change-Id: I282b38c2eee428d25319af3bc842f9feafed461c

1 files changed, 22 insertions, 3 deletions

diff --git a/gdb/breakpoint.h b/gdb/breakpoint.h
index ba28219..e412c4d 100644
--- a/gdb/breakpoint.h
+++ b/gdb/breakpoint.h
@@ -968,13 +968,31 @@ extern bpstat *build_bpstat_chain (const address_space *aspace,
    several reasons concurrently.)
 
    Each element of the chain has valid next, breakpoint_at,
-   commands, FIXME??? fields.  */
+   commands, FIXME??? fields.
+
+   watchpoints_triggered must be called beforehand to set up each
+   watchpoint's watchpoint_triggered value.
+
+*/
 
 extern bpstat *bpstat_stop_status (const address_space *aspace,
 				  CORE_ADDR pc, thread_info *thread,
 				  const target_waitstatus &ws,
 				  bpstat *stop_chain = nullptr);
+
+/* Like bpstat_stop_status, but clears all watchpoints'
+   watchpoint_triggered flag.  Unlike with bpstat_stop_status, there's
+   no need to call watchpoint_triggered beforehand.  You'll typically
+   use this variant when handling a known-non-watchpoint event, like a
+   fork or exec event.  */
+
+extern bpstat *bpstat_stop_status_nowatch (const address_space *aspace,
+					   CORE_ADDR bp_addr,
+					   thread_info *thread,
+					   const target_waitstatus &ws);
 
+
+
 /* This bpstat_what stuff tells wait_for_inferior what to do with a
    breakpoint (a challenging task).
 
@@ -1607,8 +1625,9 @@ extern void insert_single_step_breakpoint (struct gdbarch *,
    otherwise, return false.  */
 extern int insert_single_step_breakpoints (struct gdbarch *);
 
-/* Check if any hardware watchpoints have triggered, according to the
-   target.  */
+/* Check whether any hardware watchpoints have triggered or not,
+   according to the target, and record it in each watchpoint's
+   'watchpoint_triggered' field.  */
 int watchpoints_triggered (const target_waitstatus &);
 
 /* Helper for transparent breakpoint hiding for memory read and write