Messages in this thread | | | Date | Mon, 10 Dec 2018 16:30:25 +0300 | From | "Dmitry V. Levin" <> | Subject | Re: [PATCH v5 13/25] m68k: add asm/syscall.h |
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Hi Geert,
On Mon, Dec 10, 2018 at 02:06:28PM +0100, Geert Uytterhoeven wrote: > On Mon, Dec 10, 2018 at 1:41 PM Dmitry V. Levin <ldv@altlinux.org> wrote: > > On Mon, Dec 10, 2018 at 09:45:42AM +0100, Geert Uytterhoeven wrote: > > > On Mon, Dec 10, 2018 at 5:30 AM Dmitry V. Levin <ldv@altlinux.org> wrote: > > > > syscall_get_* functions are required to be implemented on all > > > > architectures in order to extend the generic ptrace API with > > > > PTRACE_GET_SYSCALL_INFO request. > > > > > > > > This introduces asm/syscall.h on m68k implementing all 5 syscall_get_* > > > > functions as documented in asm-generic/syscall.h: syscall_get_nr, > > > > syscall_get_arguments, syscall_get_error, syscall_get_return_value, > > > > and syscall_get_arch. > > > > > > > > Cc: Geert Uytterhoeven <geert@linux-m68k.org> > > > > Cc: Oleg Nesterov <oleg@redhat.com> > > > > Cc: Andy Lutomirski <luto@kernel.org> > > > > Cc: Elvira Khabirova <lineprinter@altlinux.org> > > > > Cc: Eugene Syromyatnikov <esyr@redhat.com> > > > > Cc: linux-m68k@lists.linux-m68k.org > > > > Signed-off-by: Dmitry V. Levin <ldv@altlinux.org> > > > > --- > > > > > > > > Notes: > > > > v5: added syscall_get_nr, syscall_get_arguments, syscall_get_error, > > > > and syscall_get_return_value > > > > v1: added syscall_get_arch > > > > > > > --- /dev/null > > > > +++ b/arch/m68k/include/asm/syscall.h > > > > @@ -0,0 +1,39 @@ > > > > > > > +static inline void > > > > +syscall_get_arguments(struct task_struct *task, struct pt_regs *regs, > > > > + unsigned int i, unsigned int n, unsigned long *args) > > > > +{ > > > > + BUG_ON(i + n > 6); > > > > > > Does this have to crash the kernel? > > > > This is what most of other architectures do, but we could choose > > a softer approach, e.g. use WARN_ON_ONCE instead. > > > > > Perhaps you can return an error code instead? > > > > That would be problematic given the signature of this function > > and the nature of the potential bug which would most likely be a usage error. > > Of course to handle that, the function's signature need to be changed. > Changing it has the advantage that the error handling can be done at the > caller, in common code, instead of duplicating it for all > architectures, possibly > leading to different semantics.
Given that *all* current users of syscall_get_arguments specify i == 0 (and there is an architecture that has BUG_ON(i)), it should be really a usage error to get into situation where i + n > 6, I wish a BUILD_BUG_ON could be used here instead.
I don't think it worths pushing the change of API just to convert a "cannot happen" assertion into an error that would have to be dealt with on the caller side.
-- ldv [unhandled content-type:application/pgp-signature] | |