From: Adhemerval Zanella <adhemerval.zanella@linaro.org>
To: libc-alpha@sourceware.org,
Alistair Francis <alistair23@gmail.com>,
Alistair Francis <alistair.francis@wdc.com>,
Arnd Bergmann <arnd.bergmann@linaro.org>
Subject: Re: [PATCH v6 3/3] sysv: linux: Pass 64-bit version of semctl syscall
Date: Wed, 29 Apr 2020 18:09:13 -0300 [thread overview]
Message-ID: <3bec18bd-cbee-5853-2d36-df377b6cf7cf@linaro.org> (raw)
In-Reply-To: <20200428220507.3409362-4-alistair.francis@wdc.com>
On 28/04/2020 19:05, Alistair Francis via Libc-alpha wrote:
> The semctl_syscall() function passes a union semun to the kernel. The
> union includes struct semid_ds as a member. On 32-bit architectures the
> Linux kernel provides a *_high version of the 32-bit sem_otime and
> sem_ctime values. These can be combined to get a 64-bit version of the
> time.
>
> This patch adjusts the struct semid_ds to support the *_high versions
> of sem_otime and sem_ctime. For 32-bit systems with a 64-bit time_t
> this can be used to get a 64-bit time from the two 32-bit values.
>
> Due to alignment differences between 64-bit and 32-bit variables we
> also need to set nsems to ensure it's correct.
I think this approach might trigger an issue on semid_ds definition for
time64 that I only noticed now.
Since the idea of semctl is not use a different entrypoint neither to add
aditional flag when issuing the syscall (either semctl or ipc), with this
change we need to assure that __TIMESIZE == 32 sem_otime alignment matches
__TIMESIZE == 64 one.
However for semid_ds and msqid_ds time_t members can't not properly aligned
to be expanded to 64-bit (shmid_ds has a shm_segsz field before the
timestamp fields) due to the ipc_perm header consisting of 9 32-bit words
except on parisc/powerpc/sparc. The alignment difference will make
semctl once programs states build against a semid_ds with time_t
being an 64-bit type.
So we have 2 options here:
1. Keep the semid_ds layout as the kernel expected one and add the
newer time64 timestamps at the *end*, and redefine the command
arguments that passes a struct semid_ds to use
(IPC_STAT, SEM_STAT, SEM_STAT_ANY) to indicate that the semid_ds
is a time64 one. The IPC_64 bit might be a feasible hack since
kernel won't use on possible new commands.
2. Add a new semctl64 to handle the time64 one semid_ds.
> ---
> .../unix/sysv/linux/hppa/struct__semid_ds32.h | 32 +++++++++++++
> .../unix/sysv/linux/mips/struct__semid_ds32.h | 30 ++++++++++++
> .../sysv/linux/powerpc/struct__semid_ds32.h | 32 +++++++++++++
> sysdeps/unix/sysv/linux/semctl.c | 47 +++++++++++++++++--
> .../sysv/linux/sparc/struct__semid_ds32.h | 32 +++++++++++++
> sysdeps/unix/sysv/linux/struct__semid_ds32.h | 32 +++++++++++++
> .../unix/sysv/linux/x86/struct__semid_ds32.h | 32 +++++++++++++
> 7 files changed, 233 insertions(+), 4 deletions(-)
> create mode 100644 sysdeps/unix/sysv/linux/hppa/struct__semid_ds32.h
> create mode 100644 sysdeps/unix/sysv/linux/mips/struct__semid_ds32.h
> create mode 100644 sysdeps/unix/sysv/linux/powerpc/struct__semid_ds32.h
> create mode 100644 sysdeps/unix/sysv/linux/sparc/struct__semid_ds32.h
> create mode 100644 sysdeps/unix/sysv/linux/struct__semid_ds32.h
> create mode 100644 sysdeps/unix/sysv/linux/x86/struct__semid_ds32.h
>
> diff --git a/sysdeps/unix/sysv/linux/hppa/struct__semid_ds32.h b/sysdeps/unix/sysv/linux/hppa/struct__semid_ds32.h
> new file mode 100644
> index 0000000000..9eceaaff2d
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/hppa/struct__semid_ds32.h
> @@ -0,0 +1,32 @@
> +/* HPPA implementation of the semaphore struct __semid_ds32.
> + Copyright (C) 1995-2020 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
> + modify it under the terms of the GNU Lesser General Public
> + License as published by the Free Software Foundation; either
> + version 2.1 of the License, or (at your option) any later version.
> +
> + The GNU C Library is distributed in the hope that it will be useful,
> + but WITHOUT ANY WARRANTY; without even the implied warranty of
> + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> + Lesser General Public License for more details.
> +
> + You should have received a copy of the GNU Lesser General Public
> + License along with the GNU C Library; if not, see
> + <https://www.gnu.org/licenses/>. */
> +
> +#if __WORDSIZE == 32
> +/* This is the "new" y2038 types defined after the 5.1 kernel. It allows
> + the kernel to use {o,c}time{_high} values to support a 64-bit time_t. */
> +struct __semid_ds32 {
> + struct ipc_perm sem_perm; /* operation permission struct */
> + __syscall_ulong_t sem_otime_high; /* last semop() time high */
> + __syscall_ulong_t sem_otime; /* last semop() time */
> + __syscall_ulong_t sem_ctime_high; /* last time changed by semctl() high */
> + __syscall_ulong_t sem_ctime; /* last time changed by semctl() */
> + __syscall_ulong_t sem_nsems; /* number of semaphores in set */
> + __syscall_ulong_t __glibc_reserved3;
> + __syscall_ulong_t __glibc_reserved4;
> +};
> +#endif
No need to define it for __WORDSIZE == 32, the ABI just supports it
anyway.
> diff --git a/sysdeps/unix/sysv/linux/mips/struct__semid_ds32.h b/sysdeps/unix/sysv/linux/mips/struct__semid_ds32.h
> new file mode 100644
> index 0000000000..2e3e2fc562
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/mips/struct__semid_ds32.h
> @@ -0,0 +1,30 @@
> +/* MIPS implementation of the semaphore struct __semid_ds32.
> + Copyright (C) 1995-2020 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
> + modify it under the terms of the GNU Lesser General Public
> + License as published by the Free Software Foundation; either
> + version 2.1 of the License, or (at your option) any later version.
> +
> + The GNU C Library is distributed in the hope that it will be useful,
> + but WITHOUT ANY WARRANTY; without even the implied warranty of
> + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> + Lesser General Public License for more details.
> +
> + You should have received a copy of the GNU Lesser General Public
> + License along with the GNU C Library; if not, see
> + <https://www.gnu.org/licenses/>. */
> +
> +#if __WORDSIZE == 32
> +/* This is the "new" y2038 types defined after the 5.1 kernel. It allows
> + the kernel to use {o,c}time{_high} values to support a 64-bit time_t. */
> +struct __semid_ds32 {
> + struct ipc_perm sem_perm; /* operation permission struct */
> + __syscall_ulong_t sem_otime; /* last semop time */
> + __syscall_ulong_t sem_ctime; /* last change time */
> + __syscall_ulong_t sem_nsems; /* number of semaphores in set */
> + __syscall_ulong_t sem_otime_high;
> + __syscall_ulong_t sem_ctime_high;
> +};
> +#endif
Ok, it cover mips64-n32 as well.
> diff --git a/sysdeps/unix/sysv/linux/powerpc/struct__semid_ds32.h b/sysdeps/unix/sysv/linux/powerpc/struct__semid_ds32.h
> new file mode 100644
> index 0000000000..f509db5a02
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/powerpc/struct__semid_ds32.h
> @@ -0,0 +1,32 @@
> +/* PowerPC implementation of the semaphore struct __semid_ds32.
> + Copyright (C) 1995-2020 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
> + modify it under the terms of the GNU Lesser General Public
> + License as published by the Free Software Foundation; either
> + version 2.1 of the License, or (at your option) any later version.
> +
> + The GNU C Library is distributed in the hope that it will be useful,
> + but WITHOUT ANY WARRANTY; without even the implied warranty of
> + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> + Lesser General Public License for more details.
> +
> + You should have received a copy of the GNU Lesser General Public
> + License along with the GNU C Library; if not, see
> + <https://www.gnu.org/licenses/>. */
> +
> +#if __WORDSIZE == 32
> +/* This is the "new" y2038 types defined after the 5.1 kernel. It allows
> + the kernel to use {o,c}time{_high} values to support a 64-bit time_t. */
> +struct __semid_ds32 {
> + struct ipc_perm sem_perm; /* operation permission struct */
> + __syscall_ulong_t sem_otime_high; /* last semop() time high */
> + __syscall_ulong_t sem_otime; /* last semop() time */
> + __syscall_ulong_t sem_ctime_high; /* last time changed by semctl() high */
> + __syscall_ulong_t sem_ctime; /* last time changed by semctl() */
> + __syscall_ulong_t sem_nsems; /* number of semaphores in set */
> + __syscall_ulong_t __glibc_reserved3;
> + __syscall_ulong_t __glibc_reserved4;
> +};
> +#endif
Ok.
> diff --git a/sysdeps/unix/sysv/linux/semctl.c b/sysdeps/unix/sysv/linux/semctl.c
> index 30571af49f..0634cc1abe 100644
> --- a/sysdeps/unix/sysv/linux/semctl.c
> +++ b/sysdeps/unix/sysv/linux/semctl.c
> @@ -22,8 +22,13 @@
> #include <sysdep.h>
> #include <shlib-compat.h>
> #include <errno.h>
> +#include <struct__semid_ds32.h>
> #include <linux/posix_types.h> /* For __kernel_mode_t. */
>
> +#define IPC_TIME64 \
> + (__WORDSIZE == 32 && __TIMESIZE == 64 \
> + && (!defined __SYSCALL_WORDSIZE || __SYSCALL_WORDSIZE == 32))
I think it would be better to move this definition to the common
ipc_priv.h header since it will most likely be used on msgctl
and shmctl y2038 support as well.
> +
> /* Define a `union semun' suitable for Linux here. */
> union semun
> {
> @@ -44,13 +49,47 @@ union semun
> static int
> semctl_syscall (int semid, int semnum, int cmd, union semun arg)
> {
> + int ret;
> +#if IPC_TIME64
I think we shoul add a comment stating why we need a auxiliary buffer
for STAT/STAT_ANY operations. Something like:
A temporary buffer is used to avoid both an issue where the export
semid_ds might not have follow kernel expected layout (due
sem_{o,c}time alignment in 64-bit time case) and the issue where
some kernel version might not clear the high bits when returning
then sem_{o,c}time information.
> + struct __semid_ds32 tmp;
> + struct semid_ds *orig;
> + bool restore = false;
> + if (cmd == IPC_STAT || cmd == SEM_STAT || cmd == SEM_STAT_ANY)
> + {
> + tmp = (struct __semid_ds32) {
> + .sem_perm = arg.buf->sem_perm,
> + .sem_otime = arg.buf->sem_otime,
> + .sem_ctime = arg.buf->sem_ctime,
> + .sem_nsems = arg.buf->sem_nsems,
> + };
We need to fully initialize the temporary struct to avoid a kernel
issue fixed in 4693916846269d633a3664586650dbfac2c5562f (4.14) where
kernel does not clear the timestamps high bits.
> + orig = arg.buf;
> + arg.buf = (struct semid_ds*)&tmp;
Space before &tmp.
> + restore = true;
> + }
> +#endif
> +
> #ifdef __ASSUME_DIRECT_SYSVIPC_SYSCALLS
> - return INLINE_SYSCALL_CALL (semctl, semid, semnum, cmd | __IPC_64,
> - arg.array);
> + ret = INLINE_SYSCALL_CALL (semctl, semid, semnum, cmd | __IPC_64,
> + arg.array);
> #else
> - return INLINE_SYSCALL_CALL (ipc, IPCOP_semctl, semid, semnum, cmd | __IPC_64,
> - SEMCTL_ARG_ADDRESS (arg));
> + ret = INLINE_SYSCALL_CALL (ipc, IPCOP_semctl, semid, semnum, cmd | __IPC_64,
> + SEMCTL_ARG_ADDRESS (arg));
> #endif
Ok.
> +
> +#if IPC_TIME64
> + if (ret >= 0 && restore)
> + {
> + arg.buf = orig;
> + arg.buf->sem_perm = tmp.sem_perm;
> + arg.buf->sem_otime = tmp.sem_otime
> + | ((time_t) tmp.sem_otime_high << 32);
> + arg.buf->sem_ctime = tmp.sem_ctime
> + | ((time_t) tmp.sem_ctime_high << 32);
> + arg.buf->sem_nsems = tmp.sem_nsems;
I think it would be better to use __time64_t explicit here.
> + }
> +#endif
> +
> + return ret;
> }
>
> int
> diff --git a/sysdeps/unix/sysv/linux/sparc/struct__semid_ds32.h b/sysdeps/unix/sysv/linux/sparc/struct__semid_ds32.h
> new file mode 100644
> index 0000000000..f641825d37
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/sparc/struct__semid_ds32.h
> @@ -0,0 +1,32 @@
> +/* Sparc implementation of the semaphore struct __semid_ds32.
> + Copyright (C) 1995-2020 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
> + modify it under the terms of the GNU Lesser General Public
> + License as published by the Free Software Foundation; either
> + version 2.1 of the License, or (at your option) any later version.
> +
> + The GNU C Library is distributed in the hope that it will be useful,
> + but WITHOUT ANY WARRANTY; without even the implied warranty of
> + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> + Lesser General Public License for more details.
> +
> + You should have received a copy of the GNU Lesser General Public
> + License along with the GNU C Library; if not, see
> + <https://www.gnu.org/licenses/>. */
> +
> +#if __WORDSIZE == 32
> +/* This is the "new" y2038 types defined after the 5.1 kernel. It allows
> + the kernel to use {o,c}time{_high} values to support a 64-bit time_t. */
> +struct __semid_ds32 {
> + struct ipc_perm sem_perm; /* operation permission struct */
> + __syscall_ulong_t sem_otime_high; /* last semop() time high */
> + __syscall_ulong_t sem_otime; /* last semop() time */
> + __syscall_ulong_t sem_ctime_high; /* last time changed by semctl() high */
> + __syscall_ulong_t sem_ctime; /* last time changed by semctl() */
> + __syscall_ulong_t sem_nsems; /* number of semaphores in set */
> + __syscall_ulong_t __glibc_reserved3;
> + __syscall_ulong_t __glibc_reserved4;
> +};
> +#endif
Ok.
> diff --git a/sysdeps/unix/sysv/linux/struct__semid_ds32.h b/sysdeps/unix/sysv/linux/struct__semid_ds32.h
> new file mode 100644
> index 0000000000..51ff83206d
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/struct__semid_ds32.h
> @@ -0,0 +1,32 @@
> +/* Generic implementation of the semaphore struct __semid_ds32.
> + Copyright (C) 1995-2020 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
> + modify it under the terms of the GNU Lesser General Public
> + License as published by the Free Software Foundation; either
> + version 2.1 of the License, or (at your option) any later version.
> +
> + The GNU C Library is distributed in the hope that it will be useful,
> + but WITHOUT ANY WARRANTY; without even the implied warranty of
> + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> + Lesser General Public License for more details.
> +
> + You should have received a copy of the GNU Lesser General Public
> + License along with the GNU C Library; if not, see
> + <https://www.gnu.org/licenses/>. */
> +
> +#if __WORDSIZE == 32
> +/* This is the "new" y2038 types defined after the 5.1 kernel. It allows
> + the kernel to use {o,c}time{_high} values to support a 64-bit time_t. */
> +struct __semid_ds32 {
> + struct ipc_perm sem_perm; /* operation permission struct */
> + __syscall_ulong_t sem_otime; /* last semop() time */
> + __syscall_ulong_t sem_otime_high; /* last semop() time high */
> + __syscall_ulong_t sem_ctime; /* last time changed by semctl() */
> + __syscall_ulong_t sem_ctime_high; /* last time changed by semctl() high */
> + __syscall_ulong_t sem_nsems; /* number of semaphores in set */
> + __syscall_ulong_t __glibc_reserved3;
> + __syscall_ulong_t __glibc_reserved4;
> +};
> +#endif
Ok.
> diff --git a/sysdeps/unix/sysv/linux/x86/struct__semid_ds32.h b/sysdeps/unix/sysv/linux/x86/struct__semid_ds32.h
> new file mode 100644
> index 0000000000..f65c9fc877
> --- /dev/null
> +++ b/sysdeps/unix/sysv/linux/x86/struct__semid_ds32.h
> @@ -0,0 +1,32 @@
> +/* x86 implementation of the semaphore struct __semid_ds32.
> + Copyright (C) 1995-2020 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
> + modify it under the terms of the GNU Lesser General Public
> + License as published by the Free Software Foundation; either
> + version 2.1 of the License, or (at your option) any later version.
> +
> + The GNU C Library is distributed in the hope that it will be useful,
> + but WITHOUT ANY WARRANTY; without even the implied warranty of
> + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
> + Lesser General Public License for more details.
> +
> + You should have received a copy of the GNU Lesser General Public
> + License along with the GNU C Library; if not, see
> + <https://www.gnu.org/licenses/>. */
> +
> +#ifdef __i386__
> +/* This is the "new" y2038 types defined after the 5.1 kernel. It allows
> + the kernel to use {o,c}time{_high} values to support a 64-bit time_t. */
> +struct __semid_ds32 {
> + struct ipc_perm sem_perm; /* operation permission struct */
> + __syscall_ulong_t sem_otime; /* last semop() time */
> + __syscall_ulong_t sem_otime_high; /* last semop() time high */
> + __syscall_ulong_t sem_ctime; /* last time changed by semctl() */
> + __syscall_ulong_t sem_ctime_high; /* last time changed by semctl() high */
> + __syscall_ulong_t sem_nsems; /* number of semaphores in set */
> + __syscall_ulong_t __glibc_reserved3;
> + __syscall_ulong_t __glibc_reserved4;
> +};
> +#endif
>
Ok.
next prev parent reply other threads:[~2020-04-29 21:09 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-28 22:05 [PATCH v6 0/3] Support y2038 semctl_syscall() Alistair Francis
2020-04-28 22:05 ` [PATCH v6 1/3] bits/sem.h: Split out struct semid_ds Alistair Francis
2020-04-28 22:05 ` [PATCH v6 2/3] semctl: Remove the sem-pad.h file Alistair Francis
2020-04-28 22:05 ` [PATCH v6 3/3] sysv: linux: Pass 64-bit version of semctl syscall Alistair Francis
2020-04-29 21:09 ` Adhemerval Zanella [this message]
2020-04-29 23:24 ` Alistair Francis
2020-04-30 15:06 ` Adhemerval Zanella
2020-04-30 21:25 ` Alistair Francis
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