On 07/26/2012 07:31 PM, Oleg Nesterov wrote:
Well. I agree, this needs changes. To begin with, uprobe should avoid
user_enable_single_step() which does access_process_vm(). And I suspect
uprobes have the problems with TIF_FORCED_TF logic.
Why? Shouldn't wee keep the trap flag if the instruction on which we
placed the uprobe activates it?
But I am not sure about this patch...
On 07/26, Sebastian Andrzej Siewior wrote:
@@ -1528,7 +1528,10 @@ static void handle_swbp(struct pt_regs *regs)
utask->state = UTASK_SSTEP;
if (!pre_ssout(uprobe, regs, bp_vaddr)) {
- user_enable_single_step(current);
+ if (test_tsk_thread_flag(current, TIF_SINGLESTEP))
+ uprobe->flags |= UPROBE_USER_SSTEP;
+ else
+ user_enable_single_step(current);
This is x86 specific, TIF_SINGLESTEP is not defined on every arch.
It is not defined on every arch but I wouldn't say it is 86 specific.
From the architectures which have user_enable_single_step() defined I
see
avr32 TIF_SINGLE_STEP
m68k TIF_DELAYED_TRACE
s390 TIF_SINGLE_STEP
which means those three could rename their flag so things are
consistent. The remaining architectures are
alpha
cris
h8300
score
and they don't set a flag and it seems they change the register
directly.
@@ -1569,7 +1572,10 @@ static void handle_singlestep(struct uprobe_task *utask,
struct pt_regs *regs)
put_uprobe(uprobe);
utask->active_uprobe = NULL;
utask->state = UTASK_RUNNING;
- user_disable_single_step(current);
+ if (uprobe->flags& UPROBE_USER_SSTEP)
+ uprobe->flags&= ~UPROBE_USER_SSTEP;
+ else
+ user_disable_single_step(current);
This is not enough (and I am not sure this is portable).
If SINGLESTEP was set, we should send SIGTRAP here. With this patch
we return with X86_EFLAGS_TF set, gdb will be notified only after the
next insn. And if we notify gdb, there is no need to keep X86_EFLAGS_TF.
Sending SIGTRAP is, yes.
I'm afraid this needs more thinking and new arch-dependant helpers.
Oleg.
Sebastian
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