On 26/07/22 10:30, Jason A. Donenfeld wrote:
> + l = __getrandom_nocancel (p, n, 0);
> + if (l > 0)
> + {
> + if ((size_t) l == n)
> + return; /* Done reading, success. */
> + p = (uint8_t *) p + l;
> + n -= l;
> + continue; /* Interrupted by a signal; keep going. */
> + }
> + else if (l == 0)
> + arc4random_getrandom_failure (); /* Weird, should never happen. */
> + else if (l == -EINTR)
> + continue; /* Interrupted by a signal; keep going. */
> + else if (!__ASSUME_GETRANDOM && l == -ENOSYS)
> + {
> + atomic_store_relaxed (&have_getrandom, false);
I still think there is no much gain in this optimization, the syscall will
most likely be present and it is one less static data. Also, we avoid to
use __ASSUME_GETRANDOM on generic code (all __ASSUME usage within
sysdeps and/or nptl).
> diff --git a/sysdeps/unix/sysv/linux/Makefile b/sysdeps/unix/sysv/linux/Makefile
> index 2ccc92b6b8..2f4f9784ee 100644
> --- a/sysdeps/unix/sysv/linux/Makefile
> +++ b/sysdeps/unix/sysv/linux/Makefile
> @@ -380,7 +380,8 @@ sysdep_routines += xstatconv internal_statvfs \
> open_nocancel open64_nocancel \
> openat_nocancel openat64_nocancel \
> read_nocancel pread64_nocancel \
> - write_nocancel statx_cp stat_t64_cp
> + write_nocancel statx_cp stat_t64_cp \
> + ppoll_nocancel
>
> sysdep_headers += bits/fcntl-linux.h
>
> diff --git a/sysdeps/unix/sysv/linux/Versions b/sysdeps/unix/sysv/linux/Versions
> index 65d2ceda2c..febe1ad421 100644
> --- a/sysdeps/unix/sysv/linux/Versions
> +++ b/sysdeps/unix/sysv/linux/Versions
> @@ -320,6 +320,7 @@ libc {
> __read_nocancel;
> __pread64_nocancel;
> __close_nocancel;
> + __ppoll_infinity_nocancel;
> __sigtimedwait;
> # functions used by nscd
> __netlink_assert_response;
There is no need to export on GLIBC_PRIVATE, since it is not currently usage
libc.so. Just define is a hidden (attribute_hidden).
> diff --git a/sysdeps/unix/sysv/linux/kernel-features.h b/sysdeps/unix/sysv/linux/kernel-features.h
> index 74adc3956b..75d5f953d4 100644
> --- a/sysdeps/unix/sysv/linux/kernel-features.h
> +++ b/sysdeps/unix/sysv/linux/kernel-features.h
> @@ -236,4 +236,11 @@
> # define __ASSUME_FUTEX_LOCK_PI2 0
> #endif
>
> +/* The getrandom() syscall was added in 3.17. */
> +#if __LINUX_KERNEL_VERSION >= 0x031100
> +# define __ASSUME_GETRANDOM 1
> +#else
> +# define __ASSUME_GETRANDOM 0
> +#endif
> +
> #endif /* kernel-features.h */
> diff --git a/sysdeps/unix/sysv/linux/not-cancel.h b/sysdeps/unix/sysv/linux/not-cancel.h
> index 2c58d5ae2f..d3df8fa79e 100644
> --- a/sysdeps/unix/sysv/linux/not-cancel.h
> +++ b/sysdeps/unix/sysv/linux/not-cancel.h
> @@ -23,6 +23,7 @@
> #include <sysdep.h>
> #include <errno.h>
> #include <unistd.h>
> +#include <sys/poll.h>
> #include <sys/syscall.h>
> #include <sys/wait.h>
> #include <time.h>
> @@ -77,6 +78,10 @@ __getrandom_nocancel (void *buf, size_t buflen, unsigned int flags)
> /* Uncancelable fcntl. */
> __typeof (__fcntl) __fcntl64_nocancel;
>
> +/* Uncancelable ppoll. */
> +int
> +__ppoll_infinity_nocancel (struct pollfd *fds, nfds_t nfds);
Use attribute_hidden here and remove it from sysdeps/unix/sysv/linux/Versions.
> +
> #if IS_IN (libc) || IS_IN (rtld)
> hidden_proto (__open_nocancel)
> hidden_proto (__open64_nocancel)
> @@ -87,6 +92,7 @@ hidden_proto (__pread64_nocancel)
> hidden_proto (__write_nocancel)
> hidden_proto (__close_nocancel)
> hidden_proto (__fcntl64_nocancel)
> +hidden_proto (__ppoll_infinity_nocancel)
> #endif
>
> #endif /* NOT_CANCEL_H */
Also update the hurd sysdeps/mach/hurd/not-cancel.h with a wrapper to
__poll (since it does not really support pthread cancellation).
> diff --git a/sysdeps/generic/chacha20_arch.h b/sysdeps/unix/sysv/linux/ppoll_nocancel.c
> similarity index 62%
> rename from sysdeps/generic/chacha20_arch.h
> rename to sysdeps/unix/sysv/linux/ppoll_nocancel.c
> index 1b4559ccbc..28c8761566 100644
> --- a/sysdeps/generic/chacha20_arch.h
> +++ b/sysdeps/unix/sysv/linux/ppoll_nocancel.c
> @@ -1,5 +1,5 @@
> -/* Chacha20 implementation, generic interface for encrypt.
> - Copyright (C) 2022 Free Software Foundation, Inc.
> +/* Linux ppoll syscall implementation -- non-cancellable.
> + Copyright (C) 2018-2022 Free Software Foundation, Inc.
> This file is part of the GNU C Library.
>
> The GNU C Library is free software; you can redistribute it and/or
> @@ -16,9 +16,16 @@
> License along with the GNU C Library; if not, see
> <https://www.gnu.org/licenses/>. */
>
> -static inline void
> -chacha20_crypt (uint32_t *state, uint8_t *dst, const uint8_t *src,
> - size_t bytes)
> +#include <unistd.h>
> +#include <sysdep-cancel.h>
> +#include <not-cancel.h>
> +
> +int
> +__ppoll_infinity_nocancel (struct pollfd *fds, nfds_t nfds)
> {
> - chacha20_crypt_generic (state, dst, src, bytes);
> +#ifndef __NR_ppoll_time64
> +# define __NR_ppoll_time64 __NR_ppoll
> +#endif
> + return INLINE_SYSCALL_CALL (ppoll_time64, fds, nfds, NULL, NULL, 0);
> }
> +hidden_def (__ppoll_infinity_nocancel)
Maybe just add an inline wrapper on sysdeps/unix/sysv/linux/not-cancel.h,
as for __getrandom_nocancel:
static inline int
__ppoll_infinity_nocancel (struct pollfd *fds, nfds_t nfds)
{
#ifndef __NR_ppoll_time64
# define __NR_ppoll_time64 __NR_ppoll
#endif
return INLINE_SYSCALL_CALL (ppoll_time64, fds, nfds, NULL, NULL, 0);
}
It avoids a lot of boilerplate code to add the internal symbol.
Hi Adhemerval,
On Tue, Jul 26, 2022 at 01:20:11PM -0300, Adhemerval Zanella Netto wrote:
> > + {
> > + atomic_store_relaxed (&have_getrandom, false);
>
> I still think there is no much gain in this optimization, the syscall will
> most likely be present and it is one less static data. Also, we avoid to
> use __ASSUME_GETRANDOM on generic code (all __ASSUME usage within
> sysdeps and/or nptl).
Oh! *That's* what you were talking about before. Sorry I didn't catch
your meaning the first time through.
Okay so you're alright having +1 syscall overhead on old systems, so
that new systems can have a byte less of static data. I don't hold any
opinions either way there and will defer to your expertise, so I'll get
rid of this part on v5.
> > + __ppoll_infinity_nocancel;
> > __sigtimedwait;
> > # functions used by nscd
> > __netlink_assert_response;
>
> There is no need to export on GLIBC_PRIVATE, since it is not currently usage
> libc.so. Just define is a hidden (attribute_hidden).
> Use attribute_hidden here and remove it from sysdeps/unix/sysv/linux/Versions.
>> Maybe just add an inline wrapper on sysdeps/unix/sysv/linux/not-cancel.h,
> as for __getrandom_nocancel:
> It avoids a lot of boilerplate code to add the internal symbol.
Okay I'll skip all the symbol stuff and just do the static inline like
getrandom has. Thanks for the suggestion; that's a lot simpler.
> Also update the hurd sysdeps/mach/hurd/not-cancel.h with a wrapper to
> __poll (since it does not really support pthread cancellation).
Ack.
Thanks for the comments. v5 coming up shortly.
Jason