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2011-12-13 Pedro Alves <pedro@codesourcery.com>

Browse source 
PR remote/13492

	* i386-low.c (i386_low_stopped_data_address): Avoid fetching
	DR_CONTROL unless necessary.  Extend comments.
	* linux-x86-low.c (x86_linux_prepare_to_resume): Don't write to
	DR0-3 if not used.  If any watchpoint was set, clear DR_STATUS.
This commit is contained in:
Pedro Alves 2011-12-13 16:11:26 +00:00
parent fabde4854c
commit 6210a125f8
3 changed files with 68 additions and 13 deletions
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9
gdb/gdbserver/ChangeLog
View file

@ -1,3 +1,12 @@
2011-12-13 Pedro Alves <pedro@codesourcery.com>
PR remote/13492
* i386-low.c (i386_low_stopped_data_address): Avoid fetching
DR_CONTROL unless necessary. Extend comments.
* linux-x86-low.c (x86_linux_prepare_to_resume): Don't write to
DR0-3 if not used. If any watchpoint was set, clear DR_STATUS.
2011-12-13 Yao Qi <yao@codesourcery.com>
* tracepoint.c (trace_buffer_alloc): Replace magic numbers with

56
gdb/gdbserver/i386-low.c
View file

@ -559,24 +559,60 @@ i386_low_stopped_data_address (struct i386_debug_reg_state *state,
CORE_ADDR addr = 0;
int i;
int rc = 0;
/* The current thread's DR_STATUS. We always need to read this to
check whether some watchpoint caused the trap. */
unsigned status;
/* We need DR_CONTROL as well, but only iff DR_STATUS indicates a
data breakpoint trap. Only fetch it when necessary, to avoid an
unnecessary extra syscall when no watchpoint triggered. */
int control_p = 0;
unsigned control;
/* Get the current values the inferior has. If the thread was
running when we last changed watchpoints, the mirror no longer
represents what was set in this LWP's debug registers. */
/* In non-stop/async, threads can be running while we change the
global dr_mirror (and friends). Say, we set a watchpoint, and
let threads resume. Now, say you delete the watchpoint, or
add/remove watchpoints such that dr_mirror changes while threads
are running. On targets that support non-stop,
inserting/deleting watchpoints updates the global dr_mirror only.
It does not update the real thread's debug registers; that's only
done prior to resume. Instead, if threads are running when the
mirror changes, a temporary and transparent stop on all threads
is forced so they can get their copy of the debug registers
updated on re-resume. Now, say, a thread hit a watchpoint before
having been updated with the new dr_mirror contents, and we
haven't yet handled the corresponding SIGTRAP. If we trusted
dr_mirror below, we'd mistake the real trapped address (from the
last time we had updated debug registers in the thread) with
whatever was currently in dr_mirror. So to fix this, dr_mirror
always represents intention, what we _want_ threads to have in
debug registers. To get at the address and cause of the trap, we
need to read the state the thread still has in its debug
registers.
In sum, always get the current debug register values the current
thread has, instead of trusting the global mirror. If the thread
was running when we last changed watchpoints, the mirror no
longer represents what was set in this thread's debug
registers. */
status = i386_dr_low_get_status ();
control = i386_dr_low_get_control ();
ALL_DEBUG_REGISTERS (i)
{
if (I386_DR_WATCH_HIT (status, i)
if (!I386_DR_WATCH_HIT (status, i))
continue;
if (!control_p)
{
control = i386_dr_low_get_control ();
control_p = 1;
}
/* This second condition makes sure DRi is set up for a data
watchpoint, not a hardware breakpoint. The reason is
that GDB doesn't call the target_stopped_data_address
method except for data watchpoints. In other words, I'm
being paranoiac. */
&& I386_DR_GET_RW_LEN (control, i) != 0)
watchpoint, not a hardware breakpoint. The reason is that
GDB doesn't call the target_stopped_data_address method
except for data watchpoints. In other words, I'm being
paranoiac. */
if (I386_DR_GET_RW_LEN (control, i) != 0)
{
addr = i386_dr_low_get_addr (i);
rc = 1;

12
gdb/gdbserver/linux-x86-low.c
View file

@ -655,6 +655,7 @@ static void
x86_linux_prepare_to_resume (struct lwp_info *lwp)
{
ptid_t ptid = ptid_of (lwp);
int clear_status = 0;
if (lwp->arch_private->debug_registers_changed)
{
@ -665,14 +666,23 @@ x86_linux_prepare_to_resume (struct lwp_info *lwp)
= &proc->private->arch_private->debug_reg_state;
for (i = DR_FIRSTADDR; i <= DR_LASTADDR; i++)
if (state->dr_ref_count[i] > 0)
{
x86_linux_dr_set (ptid, i, state->dr_mirror[i]);
/* If we're setting a watchpoint, any change the inferior
had done itself to the debug registers needs to be
discarded, otherwise, i386_low_stopped_data_address can
get confused. */
clear_status = 1;
}
x86_linux_dr_set (ptid, DR_CONTROL, state->dr_control_mirror);
lwp->arch_private->debug_registers_changed = 0;
}
if (lwp->stopped_by_watchpoint)
if (clear_status || lwp->stopped_by_watchpoint)
x86_linux_dr_set (ptid, DR_STATUS, 0);
}