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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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