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Subjecttest-case (Was: [PATCH 12/X] uprobes: x86: introduce abort_xol())
On 10/21, Oleg Nesterov wrote:
>
> On 10/21, Ananth N Mavinakayanahalli wrote:
> >
> > On Fri, Oct 21, 2011 at 08:12:07PM +0530, Srikar Dronamraju wrote:
> >
> > > > +void abort_xol(struct pt_regs *regs)
> > > > +{
> > > > + // !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
> > > > + // !!! Dear Srikar and Ananth, please implement me !!!
> > > > + // !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
> > > > + struct uprobe_task *utask = current->utask;
> > > > + regs->ip = utask->vaddr;
> > >
> > > nit:
> > > Shouldnt we be setting the ip to the next instruction after this
> > > instruction?
> >
> > No, since we should re-execute the original instruction
>
> Yes,

In case it was not clear, I meant "agree with your 'No'".

> > after removing
> > the breakpoint.
>
> No? we should not remove this uprobe?
>
> > Also, wrt ip being set to the next instruction on a breakpoint hit,
> > that's arch specific.
>
> Probably yes, I am not sure. But:
>
> > For instance, on x86, it points to the next
> > instruction,
>
> No?
>
> /**
> * get_uprobe_bkpt_addr - compute address of bkpt given post-bkpt regs
> * @regs: Reflects the saved state of the task after it has hit a breakpoint
> * instruction.
> * Return the address of the breakpoint instruction.
> */
> unsigned long __weak get_uprobe_bkpt_addr(struct pt_regs *regs)
> {
> return instruction_pointer(regs) - UPROBES_BKPT_INSN_SIZE;
> }
>
> Yes, initially regs->ip points to the next insn after int3, but
> utask->vaddr == get_uprobe_bkpt_addr() == addr of int3.

Ananth, Srikar, I'd suggest this test-case:

#include <stdio.h>
#include <signal.h>
#include <ucontext.h>

void *fault_insn;

static inline void *uc_ip(struct ucontext *ctxt)
{
return (void*)ctxt->uc_mcontext.gregs[16];
}
void segv(int sig, siginfo_t *info, void *ctxt)
{
static int cnt;
printf("SIGSEGV! ip=%p addr=%p\n", uc_ip(ctxt), info->si_addr);

if (uc_ip(ctxt) != fault_insn)
printf("ERR!! wrong ip\n");
if (info->si_addr != (void*)0x12345678)
printf("ERR!! wrong addr\n");
if (++cnt == 3)
signal(SIGSEGV, SIG_DFL);
}
int main(void)
{
struct sigaction sa = {
.sa_sigaction = segv,
.sa_flags = SA_SIGINFO,
};
sigaction(SIGSEGV, &sa, NULL);

fault_insn = &&label;

label:
asm volatile ("movl $0x0,0x12345678");

return 0;
}
result:

$ ulimit -c unlimited

$ ./segv
SIGSEGV! ip=0x4006eb addr=0x12345678
SIGSEGV! ip=0x4006eb addr=0x12345678
SIGSEGV! ip=0x4006eb addr=0x12345678
Segmentation fault (core dumped)

$ gdb -c ./core.1826
...
Program terminated with signal 11, Segmentation fault.
#0 0x00000000004006eb in ?? ()
Now. If you insert uprobe at asm("movl") insn, result should be the same
or the patches I sent are wrong. In particular, the addr in the coredump
should be correct too. And consumer->handler() should be called 3 times
too. This insn is really executed 3 times.

I have no idea how can I test this.

Oleg.



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