read watchpoints ignored?

[Vladimir Prus <ghost@cs.msu.su>]

Hi,
I found a situation when read watchpoints are ignored by gdb. Consider this
program:

   #include <stdio.h>

   int a, b, c;

   int main()
   {
       a = 10;
       printf("Here I am\n");

       b = a;
       c = a;

       return 0;
   }

and this gdb session:

    (gdb) b main
    Breakpoint 1 at 0x80483a4: file rw.cpp, line 8.
    (gdb) r
    Starting program: /tmp/a.out

    Breakpoint 1, main () at rw.cpp:8
    8           a = 10;
    (gdb) rwatch a
    Hardware read watchpoint 2: a
    (gdb) c
    Continuing.
    Hardware read watchpoint 2: a

    Value = 10
    0x080483bd in main () at rw.cpp:11
    11          c = a;

Expected result: gdb stops on "b = a" line.
Actual result: gdb stops on "c = a".

Here's why it happens. When breakpoint is set, gdb reads the current value
of 'a', which is zero. After continue, a is assigned the value of '10', and
then first read watchpoint fires (on "b = a"). We arrive to
"bpstat_stop_status" (breakpoint.c), which has the following code:


  else if (b->type == bp_read_watchpoint || 
             b->type == bp_access_watchpoint)
      {
        ...
        if (found)
          {
            ...
            int e = catch_errors (watchpoint_check, bs, message,
                                  RETURN_MASK_ALL);
            switch (e)
              {
              .......
              case WP_VALUE_CHANGED:
                if (b->type == bp_read_watchpoint)
                  {
                    /* Don't stop: read watchpoints shouldn't fire if
                       the value has changed.  This is for targets
                       which cannot set read-only watchpoints.  */
                    bs->print_it = print_it_noop;
                    bs->stop = 0;
                    continue;
                  }


Since value of 'a' was changed by the "a = 10" line, "watchpoint_check"
returns "WP_VALUE_CHANGED", and reporting of watchpoint is completely
suppressed.

Questions:
1. Is this a bug?
2. Can this bug be fixed by removing this inner

      if (b->type == bp_read_wathcpoint)

   statement? This will cause watchpoints to trigger more often
   on those target that don't have "read-only watchpoints", but 
   there will be no risk of missing watchpoint. And I think missed
   watchpoint is more harm then spurious watchpoint.

Opinions?

- Volodya