Messages in this thread | | | Date | Thu, 26 Jul 2012 19:31:26 +0200 | From | Oleg Nesterov <> | Subject | Re: [PATCH] uprobes: don't enable/disable signle step if the user did it |
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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.
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.
> @@ -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.
I'm afraid this needs more thinking and new arch-dependant helpers.
Oleg.
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