Re: [PATCH] PR threads/10729: x86 hw watchpoints and non-stop mode

Pedro Alves
2011-12-12T20:30:44Z

Thanks again for the test.

I'm wondering why bother to mask out DR_STATUS bits instead
of clearing all of it. I mean, when we set a watchpoint, we're
already clobbering the whole of DR_CONTROL, with

i386_dr_low.set_control (new_state->dr_control_mirror);

so it seems there's no point in trying to retain all the other
bits of DR_STATUS. If we set a watchpoint, any change the
inferior had done itself to the debug registers is thrown
out the window.

If I change amd64_linux_prepare_to_resume to look like:

static void
amd64_linux_prepare_to_resume (struct lwp_info *lwp)
{
int clear_status = 0;

if (lwp->arch_private->debug_registers_changed)
{
struct i386_debug_reg_state *state = i386_debug_reg_state ();
int i;

for (i = DR_FIRSTADDR; i <= DR_LASTADDR; i++)
if (state->dr_ref_count[i] > 0)
{
amd64_linux_dr_set (lwp->ptid, i, state->dr_mirror[i]);

/* Only a sanity check for leftover bits (set possibly
only by inferior). */
clear_status = 1;
}

amd64_linux_dr_set (lwp->ptid, DR_CONTROL, state->dr_control_mirror);

lwp->arch_private->debug_registers_changed = 0;
}

if (clear_status || lwp->stopped_by_watchpoint)
amd64_linux_dr_set (lwp->ptid, DR_STATUS, 0);
}

(the `clear_status' bits are new) then the new test passes.

I'm doing a full run with this now.

--
Pedro Alves