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    SubjectRe: test-case (Was: [PATCH 12/X] uprobes: x86: introduce abort_xol())
    > 
    > 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.
    >

    I have tested this on both x86_32 and x86_64 and can confirm that the
    behaviour is same with or without uprobes placed at that instruction.
    This is on the uprobes code with your changes.

    However on x86_32; the output is different from x86_64.

    On x86_32 (I have additionally printed the uc_ip and fault_insn.

    SIGSEGV! ip=0x10246 addr=0x12345678
    ERR!! wrong ip uc_ip(ctxt) = 10246 fault_insn = 804856c
    SIGSEGV! ip=0x10246 addr=0x12345678
    ERR!! wrong ip uc_ip(ctxt) = 10246 fault_insn = 804856c
    SIGSEGV! ip=0x10246 addr=0x12345678
    ERR!! wrong ip uc_ip(ctxt) = 10246 fault_insn = 804856c
    Segmentation fault

    the fault_insn matches the address shown in disassemble of gdb.
    I still trying to dig up what uc_ip is and why its different on x86_32.

    On x86_64 the result is what you pasted above.


    Also I was thinking on your suggestion of making abort_xol a weak
    function. In which case we could have architecture independent function
    in kernel/uprobes.c which is just a wrapper for set_instruction_pointer.

    void __weak abort_xol(struct pt_regs *regs, struct uprobe_task *utask)
    {
    set_instruction_pointer(regs, utask->vaddr);
    }

    where it would called from uprobe_notify_resume() as

    abort_xol(regs, utask);

    If other archs would want to do something else, they could override
    abort_xol definition.

    --
    Thanks and Regards
    Srikar



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