Re: [PATCH 11/13] tools/nolibc: sys_select: riscv: use __NR_pselect6_time64 for rv32

Thomas Weißschuh
2023-05-25T07:28:36Z

On 2023-05-25 15:10:21+0800, Zhangjin Wu wrote:
> Hi, Thomas
>
> > On 2023-05-25 01:59:55+0800, Zhangjin Wu wrote:
> > > rv32 uses the generic include/uapi/asm-generic/unistd.h and it has no
> > > __NR_pselect6 after kernel commit d4c08b9776b3 ("riscv: Use latest
> > > system call ABI"), use __NR_pselect6_time64 instead.
> > >
> > > Signed-off-by: Zhangjin Wu <falcon@tinylab.org>
> > > ---
> > > tools/include/nolibc/sys.h | 7 ++++++-
> > > 1 file changed, 6 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/tools/include/nolibc/sys.h b/tools/include/nolibc/sys.h
> > > index c0335a84f880..00c7197dcd50 100644
> > > --- a/tools/include/nolibc/sys.h
> > > +++ b/tools/include/nolibc/sys.h
> > > @@ -1041,8 +1041,13 @@ int sys_select(int nfds, fd_set *rfds, fd_set *wfds, fd_set *efds, struct timeva
> > > struct timeval *t;
> > > } arg = { .n = nfds, .r = rfds, .w = wfds, .e = efds, .t = timeout };
> > > return my_syscall1(__NR_select, &arg);
> > > -#elif defined(__ARCH_WANT_SYS_PSELECT6) && defined(__NR_pselect6)
> > > +#elif defined(__ARCH_WANT_SYS_PSELECT6) && (defined(__NR_pselect6) || defined(__NR_pselect6_time64))
> > > +#ifdef __NR_pselect6
> > > struct timespec t;
> > > +#else
> > > + struct timespec64 t;
> > > +#define __NR_pselect6 __NR_pselect6_time64
> >
> > Wouldn't this #define leak to the users of nolibc and lead to calls to
> > pselect6_time64 with the ABI of the __NR_pselect6 if userspace is doing
> > its own raw syscalls?
> >
>
> Yeah, it would break the user-side raw __NR_pselect6 syscall for nolibc is a
> header-only libc, so, it is not safe to use such method like glibc.
>
> Something like this will let the syscall call to pselect6_time64 instead of the
> user-required __NR_pselect6 and pass the wrong type of argument.
>
> #include "nolibc.h" // If no __NR_pselect6 defined, __NR_pselect6 = __NR_pselect6_time64
>
> #ifdef __NR_pselect6
> struct timespec t; // come here for __NR_pselect6_time64, but t is not timespec64, broken
> syscall(__NR_pselect6, nfds, rfds, wfds, efds, timeout ? &t : NULL, NULL);
> #else
> struct timespec64 t;
> syscall(__NR_pselect6, nfds, rfds, wfds, efds, timeout ? &t : NULL, NULL);
> #endif
>
> I have used something like __NR_pselect6_time3264 locally, before
> sending the patchset, I found a cleaner method already used in sys.h:
>
> #ifndef __NR__newselect
> #define __NR__newselect __NR_select
> #endif
>
> But I forgot the arguments mixing issue, __NR__newselect and __NR_select
> share the same type of arguments, but __NR_pselect6 and
> __NR_pselect6_time64 not, so, I will use back the old method but still
> need to find a better string, just like __NR__newselect, __NR__pselect6
> may be used in kernel space in the future, and __NR_pselect6_time3264 is
> too long, what about this?
>
> #ifdef __NR_pselect6
> struct timespec t;
> #define __NR_pselect6__ __NR_pselect6
> #else
> struct timespec64 t;
> #define __NR_pselect6__ __NR_pselect6_time64
> #endif
>
> Or even ___NR_pselect6?

What about:

#ifdef __NR_pselect6
struct timespec t;
const long nr_pselect = __NR_pselect6;
#else
struct timespec64 t;
const long nr_pselect = __NR_pselect6_time64;
#endif

>
> The same issue is in this patch:
>
> [PATCH 13/13] tools/nolibc: sys_gettimeofday: riscv: use __NR_clock_gettime64
>
> will solve it with the same method.

Thanks!