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Re: [PATCH v2] sysv: linux: Pass 64-bit version of semctl syscall
- From: Adhemerval Zanella <adhemerval dot zanella at linaro dot org>
- To: libc-alpha at sourceware dot org
- Date: Fri, 21 Feb 2020 11:03:24 -0300
- Subject: Re: [PATCH v2] sysv: linux: Pass 64-bit version of semctl syscall
- References: <20200205005610.31739-1-alistair.francis@wdc.com>
On 04/02/2020 21:56, Alistair Francis 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 union semun to include a struct __semid_ds32
> which supports 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.
> ---
> v2:
> - Fix the HPPA error
> - Simplfy the code changes
>
> include/sys/sem.h | 35 +++++++++++++++++++
> sysdeps/unix/sysv/linux/bits/sem-pad.h | 1 +
> sysdeps/unix/sysv/linux/hppa/bits/sem-pad.h | 2 ++
> sysdeps/unix/sysv/linux/mips/bits/sem-pad.h | 2 ++
> .../unix/sysv/linux/powerpc/bits/sem-pad.h | 2 ++
> sysdeps/unix/sysv/linux/semctl.c | 23 +++++++++---
> sysdeps/unix/sysv/linux/sparc/bits/sem-pad.h | 2 ++
> sysdeps/unix/sysv/linux/x86/bits/sem-pad.h | 1 +
> 8 files changed, 64 insertions(+), 4 deletions(-)
>
> diff --git a/include/sys/sem.h b/include/sys/sem.h
> index 69fdf1f752..70b83127cb 100644
> --- a/include/sys/sem.h
> +++ b/include/sys/sem.h
> @@ -5,5 +5,40 @@
>
> __typeof__ (semtimedop) __semtimedop attribute_hidden;
>
> +# endif
> +
> +# ifdef __SEMID_DS_HIGH
> +# if defined (__SEMID_DS_HIGH_END)
The current idea for per-architecture overrides is to define the expected
default value on the generic header and check for the value *value* instead
of *existence*. So here it should be:
#if __SEMID_DS_HIGH
# if __SEMID_DS_HIGH_END
...
# elif __SEMID_DS_HIGH_SWAP
...
# else
# endif
#endif
So you need to define __SEMID_DS_HIGH, __SEMID_DS_HIGH_END, and
__SEMID_DS_HIGH_SWAP for all architectures (this is how __SEM_PAD_BEFORE_TIME
and __SEM_PAD_AFTER_TIME are organized).
And I think it might be worth to add a _Static_assert to avoid possible
errors if an architecture wrongly set __SEMID_DS_HIGH_END and __SEMID_DS_HIGH_SWAP:
#if __SEMID_DS_HIGH
# if __SEMID_DS_HIGH_END
_Static_assert (!__SEMID_DS_HIGH_SWAP, "__SEMID_DS_HIGH_SWAP if defined");
...
# elif __SEMID_DS_HIGH_SWAP
...
# else
# endif
#endif
> +struct __semid_ds32 {
> + struct ipc_perm sem_perm; /* permissions .. see ipc.h */
> + __syscall_ulong_t sem_otime; /* last semop time */
> + __syscall_ulong_t sem_ctime; /* last change time */
> + __syscall_ulong_t sem_nsems; /* no. of semaphores in array */
> + __syscall_ulong_t sem_otime_high;
> + __syscall_ulong_t sem_ctime_high;
> +};
> +# elif defined (__SEMID_DS_HIGH_SWAP)
> +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;
> +};
> +# else
> +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
> # endif
> #endif
>From my pthread refactoring, I wonder if would be better to parametriz the
semid_ds instead and define the sem_{o,c}time{_time} directly on the structure
instead of adding define layer.
So we will have an installed Linux semid_ds_t.h header which Linux sem.h includes
and each architecture redefines if required. It would allow to add the requires
y2038 fields you are proposing and semctl will change it directly.
> diff --git a/sysdeps/unix/sysv/linux/bits/sem-pad.h b/sysdeps/unix/sysv/linux/bits/sem-pad.h
> index 566ce039cc..18235e56df 100644
> --- a/sysdeps/unix/sysv/linux/bits/sem-pad.h
> +++ b/sysdeps/unix/sysv/linux/bits/sem-pad.h
> @@ -31,3 +31,4 @@
>
> #define __SEM_PAD_AFTER_TIME (__TIMESIZE == 32)
> #define __SEM_PAD_BEFORE_TIME 0
> +#define __SEMID_DS_HIGH (__WORDSIZE == 32)
> diff --git a/sysdeps/unix/sysv/linux/hppa/bits/sem-pad.h b/sysdeps/unix/sysv/linux/hppa/bits/sem-pad.h
> index ee0332325b..62580792b3 100644
> --- a/sysdeps/unix/sysv/linux/hppa/bits/sem-pad.h
> +++ b/sysdeps/unix/sysv/linux/hppa/bits/sem-pad.h
> @@ -24,3 +24,5 @@
>
> #define __SEM_PAD_AFTER_TIME 0
> #define __SEM_PAD_BEFORE_TIME (__TIMESIZE == 32)
> +#define __SEMID_DS_HIGH (__WORDSIZE == 32)
> +#define __SEMID_DS_HIGH_SWAP (__WORDSIZE == 32)
> diff --git a/sysdeps/unix/sysv/linux/mips/bits/sem-pad.h b/sysdeps/unix/sysv/linux/mips/bits/sem-pad.h
> index 4c581f7694..12f2bd9c62 100644
> --- a/sysdeps/unix/sysv/linux/mips/bits/sem-pad.h
> +++ b/sysdeps/unix/sysv/linux/mips/bits/sem-pad.h
> @@ -22,3 +22,5 @@
>
> #define __SEM_PAD_AFTER_TIME 0
> #define __SEM_PAD_BEFORE_TIME 0
> +#define __SEMID_DS_HIGH (__WORDSIZE == 32)
> +#define __SEMID_DS_HIGH_END (__WORDSIZE == 32)
> diff --git a/sysdeps/unix/sysv/linux/powerpc/bits/sem-pad.h b/sysdeps/unix/sysv/linux/powerpc/bits/sem-pad.h
> index 42d8827906..a13ca5f6bd 100644
> --- a/sysdeps/unix/sysv/linux/powerpc/bits/sem-pad.h
> +++ b/sysdeps/unix/sysv/linux/powerpc/bits/sem-pad.h
> @@ -24,3 +24,5 @@
>
> #define __SEM_PAD_AFTER_TIME 0
> #define __SEM_PAD_BEFORE_TIME (__TIMESIZE == 32)
> +#define __SEMID_DS_HIGH (__WORDSIZE == 32)
> +#define __SEMID_DS_HIGH_SWAP (__WORDSIZE == 32)
> diff --git a/sysdeps/unix/sysv/linux/semctl.c b/sysdeps/unix/sysv/linux/semctl.c
> index 0c3eb0932f..8dcb012b0b 100644
> --- a/sysdeps/unix/sysv/linux/semctl.c
> +++ b/sysdeps/unix/sysv/linux/semctl.c
> @@ -28,6 +28,9 @@ union semun
> {
> int val; /* value for SETVAL */
> struct semid_ds *buf; /* buffer for IPC_STAT & IPC_SET */
> +#ifdef __SEMID_DS_HIGH
> + struct __semid_ds32 *buf32; /* buffer for IPC_STAT & IPC_SET on 32-bit systems */
> +#endif
> unsigned short int *array; /* array for GETALL & SETALL */
> struct seminfo *__buf; /* buffer for IPC_INFO */
> };
> @@ -43,13 +46,25 @@ union semun
> static int
> semctl_syscall (int semid, int semnum, int cmd, union semun arg)
> {
> + int ret;
> #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
> +#ifdef __SEMID_DS_HIGH
> +/* If we aren't going to overflow the time_t sem_ctime/sem_otime set it */
> +# if __TIMESIZE == 64 && __WORDSIZE == 32
My understanding is for the SysV IPC y2038-safe call it should be done with
a different IPC_STAT value than current one (with the __IPC_64 bit set).
So I think a better strategy would be to:
1. Check if IPC_STAT has the __IPC_64 bit set.
2. Only set the y2038 safe values if command also has __IPC_64 bit set.
3. Adjust all the requires architecture to have IPC_STAT with __IPC_64 set.
4. For time32 symbol, clear the __IPC_64 bit.
So here it would be:
[...]
#define __IPC_TIME64 (IPC_STAT & __IPC_64)
[...]
#if __IPC_TIME64
if (ret == 0 && (cmd & __IPC_TIME64))
{
[...]
}
#endif
It wouldn't be active since IPC_STAT does not have IPC_64 set currently.
> + if (ret == 0)
> + {
> + arg.buf->sem_ctime = arg.buf32->sem_ctime | ((time_t) arg.buf32->sem_ctime_high << 32);
> + arg.buf->sem_otime = arg.buf32->sem_otime | ((time_t) arg.buf32->sem_otime_high << 32);
> + }
> +# endif
Line too long.
> +#endif
> + return ret;
> }
>
> int
> diff --git a/sysdeps/unix/sysv/linux/sparc/bits/sem-pad.h b/sysdeps/unix/sysv/linux/sparc/bits/sem-pad.h
> index 5f4e214d12..79655b8149 100644
> --- a/sysdeps/unix/sysv/linux/sparc/bits/sem-pad.h
> +++ b/sysdeps/unix/sysv/linux/sparc/bits/sem-pad.h
> @@ -24,3 +24,5 @@
>
> #define __SEM_PAD_AFTER_TIME 0
> #define __SEM_PAD_BEFORE_TIME (__TIMESIZE == 32)
> +#define __SEMID_DS_HIGH (__WORDSIZE == 32)
> +#define __SEMID_DS_HIGH_SWAP (__WORDSIZE == 32)
> diff --git a/sysdeps/unix/sysv/linux/x86/bits/sem-pad.h b/sysdeps/unix/sysv/linux/x86/bits/sem-pad.h
> index 102e226997..db397857e7 100644
> --- a/sysdeps/unix/sysv/linux/x86/bits/sem-pad.h
> +++ b/sysdeps/unix/sysv/linux/x86/bits/sem-pad.h
> @@ -22,3 +22,4 @@
>
> #define __SEM_PAD_AFTER_TIME 1
> #define __SEM_PAD_BEFORE_TIME 0
> +#define __SEMID_DS_HIGH 1
>