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    SubjectRe: [RFC][PATCH] Demultiplexing SIGTRAP signal

    * Srinivasa Ds <srinivasa@in.ibm.com> wrote:

    > Currently a SIGTRAP signal can denote any one of below reasons.
    > - Breakpoint hit
    > - H/W debug register hit
    > - Single step
    > - SIGTRAP signal sent through kill() or rasie()
    >
    > Architectures like powerpc/parisc provides infrastructure to
    > demultiplex SIGTRAP signal by passing down the information for
    > receiving SIGTRAP through si_code of siginfot_t structure. Here is an
    > attempt is generalise this infrastructure by extending it to x86 and
    > x86_64 archs.

    no fundamental objections - assuming existing x86 apps have not grown an
    ABI dependency on the existing send_sigtrap() semantics. (Debuggers and
    JITs would be a candidate for such dependencies.)

    a small implementational detail, this bit:

    > @@ -935,8 +936,22 @@ void __kprobes do_debug(struct pt_regs *
    > goto clear_TF_reenable;
    > }
    >
    > - /* Ok, finally something we can handle */
    > - send_sigtrap(tsk, regs, error_code);
    > + tsk->thread.trap_no = 1;
    > + tsk->thread.error_code = error_code;
    > +
    > + memset(&info, 0, sizeof(info));
    > + info.si_signo = SIGTRAP;
    > + if (condition & DR_STEP)
    > + info.si_code = TRAP_TRACE;
    > + else if (condition & (DR_TRAP0|DR_TRAP1|DR_TRAP2|DR_TRAP3))
    > + info.si_code = TRAP_HWBKPT;
    > + else
    > + info.si_code = TRAP_BRKPT;
    > + /* User-mode ip? */
    > + info.si_addr = user_mode_vm(regs) ? (void __user *) regs->ip : NULL;
    > +
    > + /* Send us the fake SIGTRAP */
    > + force_sig_info(SIGTRAP, &info, tsk);

    should be pushed into [a sufficiently extended] send_sigtrap() instead.

    and this bit:

    > - info.si_code = TRAP_BRKPT;
    > + if (condition & DR_STEP)
    > + info.si_code = TRAP_TRACE;
    > + else if (condition & (DR_TRAP0|DR_TRAP1|DR_TRAP2|DR_TRAP3))
    > + info.si_code = TRAP_HWBKPT;
    > + else
    > + info.si_code = TRAP_BRKPT;

    should be separated into a helper function as well i guess.

    Roland, any objections to the core idea (or to the implementation)?

    Ingo


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