Messages in this thread | | | From | Geert Uytterhoeven <> | Date | Sat, 30 Mar 2019 21:57:46 +0100 | Subject | Re: [PATCH v5 13/25] m68k: add asm/syscall.h |
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CC Steven
On Fri, Mar 29, 2019 at 11:04 PM Dmitry V. Levin <ldv@altlinux.org> wrote: > On Wed, Dec 12, 2018 at 11:55:16AM +0300, Dmitry V. Levin wrote: > > On Mon, Dec 10, 2018 at 04:30:25PM +0300, Dmitry V. Levin wrote: > > > 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. > > > > I suggest the following BUG_ON replacement for syscall_get_arguments: > > > > #define SYSCALL_MAX_ARGS 6 > > > > static inline void > > syscall_get_arguments(struct task_struct *task, struct pt_regs *regs, > > unsigned int i, unsigned int n, unsigned long *args) > > { > > /* > > * Ideally there should have been > > * BUILD_BUG_ON(i + n > SYSCALL_MAX_ARGS); > > * instead of these checks. > > */ > > if (unlikely(i > SYSCALL_MAX_ARGS)) { > > WARN_ONCE(1, "i > SYSCALL_MAX_ARGS"); > > return; > > } > > if (unlikely(n > SYSCALL_MAX_ARGS - i)) { > > WARN_ONCE(1, "i + n > SYSCALL_MAX_ARGS"); > > n = SYSCALL_MAX_ARGS - i; > > } > > BUILD_BUG_ON(sizeof(regs->d1) != sizeof(args[0])); > > memcpy(args, ®s->d1 + i, n * sizeof(args[0])); > > } > > There seems to be a more straightforward approach to this issue. > > Assuming there is a general consensus [1] to get rid of "i" and "n" > arguments of syscall_get_arguments(), the implementation could be > simplified to > > static inline void > syscall_get_arguments(struct task_struct *task, struct pt_regs *regs, > unsigned long *args) > { > memcpy(args, ®s->d1, 6 * sizeof(args[0])); > } > > [1] https://lore.kernel.org/lkml/20190328230512.486297455@goodmis.org/
Yeah, no longer a need for all these ugly checks, good.
Gr{oetje,eeting}s,
Geert
-- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
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