Re: Fwd: arch/ && tracehook_report_syscall_xxx()

Ingo Molnar
2009-04-29T19:31:42Z

* Oleg Nesterov <oleg@redhat.com> wrote:

> On 04/27, Christoph Hellwig wrote:
> >
> > I've poked a few arch maintainers in the past to separate the enter/exit
> > path and usually got the desired changes :)
>
> I'd like to try your method!
>
> So. Dear maintainers of
>
> alpha
> arm
> avr32
> blackfin
> cris
> h8300
> m32r
> m68k
> m68knommu
> mips
> parisc
> um
> xtensa
>
> . Could you please convert your syscall trace code to use
> tracehook_report_syscall_entry/tracehook_report_syscall_exit ?
>
>
> For example, let's look at more or less typical arch/alpha/kernel/ptrace.c,
>
> asmlinkage void
> syscall_trace(void)
> {
> if (!test_thread_flag(TIF_SYSCALL_TRACE))
> return;
> if (!(current->ptrace & PT_PTRACED))
> return;
> /* The 0x80 provides a way for the tracing parent to distinguish
> between a syscall stop and SIGTRAP delivery */
> ptrace_notify(SIGTRAP | ((current->ptrace & PT_TRACESYSGOOD)
> ? 0x80 : 0));
>
> /*
> * This isn't the same as continuing with a signal, but it will do
> * for normal use. strace only continues with a signal if the
> * stopping signal is not SIGTRAP. -brl
> */
> if (current->exit_code) {
> send_sig(current->exit_code, current, 1);
> current->exit_code = 0;
> }
> }
>
> it would be really nice to turn it into something like
>
> asmlinkage void
> syscall_trace(int entryexit)
> {
> if (!test_thread_flag(TIF_SYSCALL_TRACE))
> return;
>
> if (entryexit)
> tracehook_report_syscall_entry(task_pt_regs(current));
> else
> tracehook_report_syscall_exit(task_pt_regs(current), stepping);
> }
>
> Also, tracehook_report_syscall_entry() might want to abort this system
> call (please see the comment above this helper), it would be great to
> take the returned value into account.
>
> arch/* play with ptrace internals which should be changed soon, not good.

And there's upstream examples in:

arch/ia64/kernel/ptrace.c
arch/powerpc/kernel/ptrace.c
arch/s390/kernel/ptrace.c
arch/sh/kernel/ptrace_32.c
arch/sh/kernel/ptrace_64.c
arch/sparc/kernel/ptrace_32.c
arch/sparc/kernel/ptrace_64.c
arch/x86/kernel/ptrace.c

as well, for tracehook usage. Chances are that your architecture's
syscall entry/exit ptrace hooks look quite similar to one of the
architectures above!

Ingo