Shaohua Li wrote: > On Wed, 2007-10-17 at 16:56 +0200, Petr Tesarik wrote: >> Shaohua Li wrote: >>> On Fri, 2007-09-07 at 09:11 -0600, David Mosberger-Tang wrote: >>>> Anything that avoids complicating the kernel exit path is worth doing! >>>> The exit path is complicated enough as it is. >>>> >>>> --david >>>> >>>> On 9/7/07, Petr Tesarik <ptesarik@xxxxxxx> wrote: >>>>> -----BEGIN PGP SIGNED MESSAGE----- >>>>> Hash: SHA1 >>>>> >>>>> Shaohua Li wrote: >>>>>> On Thu, 2007-09-06 at 15:59 +0200, Petr Tesarik wrote: >>>>>>> [...] >>>>>>> So, what happens if upon syscall entry notification the debugger >>>>>>> modifies the part of the RBS (in user-space) which corresponds to the >>>>>>> arguments of that syscall? Currently, the syscall takes the modified >>>>>>> arguments, but with your change it would still take the stale data >>>>>>> from >>>>>>> the kernel RBS. >>>>>> The patch does sync from user RBS to kernel RBS just after syscall trace >>>>>> enter. this is an exception I said doing sync just before syscall >>>>>> return. I thought this covers your case, no? >>>>> Ah, I'm sorry, I missed that part of the patch. Well, if we have to do a >>>>> sync on every syscall_trace_enter() and syscall_trace_leave(), then the >>>>> only cases where introducing TIF_RESTORE_RSE saves us a duplicate sync >>>>> seems to be in the clone/fork and exit paths. In other words, it's >>>>> probably not worth the added complexity. But since you have written the >>>>> whole complex thing already, I have no objections against it. >>> Ok, this is a simplified patch. please review. >> Well, it's been quite some time, but here we go. >> >> I'm generally fine with this patch, but pleas note that it can't be >> included on its own: >> >> 1. There still is the race condition introduced by moving >> set_current_state(TASK_TRACED) after the spin_unlock_irq > I don't know the details, but Roland said if other parts are ok, he can help fix the issue. > >> 2. You must couple it with the (planned) changes to the ptrace, >> because otherwise PTRACE_{PEEK,POKE}{TEXT,DATA} still access the kernel >> RBS, but it gets later overwritten back from userspace when it is synced. > >> I have verified that failing to do so breaks "strace -f", because >> strace >> relies on intercepting the clone() system call and setting the >> CLONE_PTRACE bit in the flags argument. Of course, if the bit is only >> set in the kernel RBS, which is overwritten with the (old) value from >> the user RBS on a PTRACE_CONT, the new process is not traced. > The patch sync kernel RBS to user just before the task is suspended, so > I think we should be fine here. I did test 'strace -f', and test is ok. Maybe you're right. I was porting this to 2.6.16 for SUSE Linux Enterprise Server 10, so my patch was a bit different. I'll retest with latest git. Nevertheless, I still think that ia64_poke() can't do the right thing here, because the changes made by PTRACE_PEEKDATA should also be visible in /proc/<pid>/mem, for example. Cheers, Petr Tesarik - To unsubscribe from this list: send the line "unsubscribe linux-ia64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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