[1/8] watch_command_1: Fix dangling frame access
Commit Message
While working on some changes to switch_to_thread, I inadvertently
make switch_to_thread call reinit_frame_cache more frequently, even
when the thread didn't change. This exposed a latent bug in
watch_command_1, where we're referencing a frame after
creating/inserting breakpoints, which potentially calls
reinit_frame_cache if it needs to install breakpoints with a different
thread selected.
Handle this similarly to how it's already handled in other similar
cases. I.e., save any frame-related information we might need before
creating a breakpoint.
gdb/ChangeLog:
yyyy-mm-dd Pedro Alves <palves@redhat.com>
* breakpoint.c (watch_command_1): Save watchpoint-frame info
before calling create_internal_breakpoint.
---
gdb/breakpoint.c | 34 +++++++++++++++++++++-------------
1 file changed, 21 insertions(+), 13 deletions(-)
Comments
Pedro Alves <palves@redhat.com> writes:
> - if (exp_valid_block && frame)
> + if (exp_valid_block && wp_frame)
if (exp_valid_block != NULL && wp_frame != NULL)
Patch is good to me.
On 04/13/2017 10:34 AM, Yao Qi wrote:
> Pedro Alves <palves@redhat.com> writes:
>
>> - if (exp_valid_block && frame)
>> + if (exp_valid_block && wp_frame)
>
> if (exp_valid_block != NULL && wp_frame != NULL)
>
> Patch is good to me.
Thanks! I did that change, and pushed patches 1-6, up until the
one that add cdtors to struct inferior.
I went ahead because last my non-POD + memset detector flagged
struct inferior, and also because I saw that Sergio's C++fy
environ patch was adding yet another non-POD member to
struct inferior.
Thanks,
Pedro Alves
@@ -11100,7 +11100,6 @@ watch_command_1 (const char *arg, int accessflag, int from_tty,
const struct block *exp_valid_block = NULL, *cond_exp_valid_block = NULL;
struct value *val, *mark, *result;
int saved_bitpos = 0, saved_bitsize = 0;
- struct frame_info *frame;
const char *exp_start = NULL;
const char *exp_end = NULL;
const char *tok, *end_tok;
@@ -11278,35 +11277,44 @@ watch_command_1 (const char *arg, int accessflag, int from_tty,
if (*tok)
error (_("Junk at end of command."));
- frame = block_innermost_frame (exp_valid_block);
+ frame_info *wp_frame = block_innermost_frame (exp_valid_block);
+
+ /* Save this because create_internal_breakpoint below invalidates
+ 'wp_frame'. */
+ frame_id watchpoint_frame = get_frame_id (wp_frame);
/* If the expression is "local", then set up a "watchpoint scope"
breakpoint at the point where we've left the scope of the watchpoint
expression. Create the scope breakpoint before the watchpoint, so
that we will encounter it first in bpstat_stop_status. */
- if (exp_valid_block && frame)
+ if (exp_valid_block && wp_frame)
{
- if (frame_id_p (frame_unwind_caller_id (frame)))
+ struct frame_id caller_frame_id = frame_unwind_caller_id (wp_frame);
+
+ if (frame_id_p (caller_frame_id))
{
+ gdbarch *caller_arch = frame_unwind_caller_arch (wp_frame);
+ CORE_ADDR caller_pc = frame_unwind_caller_pc (wp_frame);
+
scope_breakpoint
- = create_internal_breakpoint (frame_unwind_caller_arch (frame),
- frame_unwind_caller_pc (frame),
+ = create_internal_breakpoint (caller_arch, caller_pc,
bp_watchpoint_scope,
&momentary_breakpoint_ops);
+ /* create_internal_breakpoint could invalidate WP_FRAME. */
+ wp_frame = NULL;
+
scope_breakpoint->enable_state = bp_enabled;
/* Automatically delete the breakpoint when it hits. */
scope_breakpoint->disposition = disp_del;
/* Only break in the proper frame (help with recursion). */
- scope_breakpoint->frame_id = frame_unwind_caller_id (frame);
+ scope_breakpoint->frame_id = caller_frame_id;
/* Set the address at which we will stop. */
- scope_breakpoint->loc->gdbarch
- = frame_unwind_caller_arch (frame);
- scope_breakpoint->loc->requested_address
- = frame_unwind_caller_pc (frame);
+ scope_breakpoint->loc->gdbarch = caller_arch;
+ scope_breakpoint->loc->requested_address = caller_pc;
scope_breakpoint->loc->address
= adjust_breakpoint_address (scope_breakpoint->loc->gdbarch,
scope_breakpoint->loc->requested_address,
@@ -11378,9 +11386,9 @@ watch_command_1 (const char *arg, int accessflag, int from_tty,
else
b->cond_string = 0;
- if (frame)
+ if (frame_id_p (watchpoint_frame))
{
- w->watchpoint_frame = get_frame_id (frame);
+ w->watchpoint_frame = watchpoint_frame;
w->watchpoint_thread = inferior_ptid;
}
else