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f991f01571
Most architectures now use the asm-generic copy of the sysvipc data
structures (msqid64_ds, semid64_ds, shmid64_ds), which use 32-bit
__kernel_time_t on 32-bit architectures but have padding behind them to
allow extending the type to 64-bit.
Unfortunately, that fails on all big-endian architectures, which have the
padding on the wrong side. As so many of them get it wrong, we decided to
not bother even trying to fix it up when we introduced the asm-generic
copy. Instead we always use the padding word now to provide the upper
32 bits of the seconds value, regardless of the endianess.
A libc implementation on a typical big-endian system can deal with
this by providing its own copy of the structure definition to user
space, and swapping the two 32-bit words before returning from the
semctl/shmctl/msgctl system calls.
Note that msqid64_ds and shmid64_ds were broken on x32 since commit
f4b4aae182 ("x86/headers/uapi: Fix __BITS_PER_LONG value for x32
builds"). I have sent a separate fix for that, but as we no longer
have to worry about x32 here, I no longer worry about x32 here and
use 'unsigned long' instead of __kernel_ulong_t.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
46 lines
1.5 KiB
C
46 lines
1.5 KiB
C
/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
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#ifndef __ASM_GENERIC_SEMBUF_H
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#define __ASM_GENERIC_SEMBUF_H
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#include <asm/bitsperlong.h>
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/*
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* The semid64_ds structure for x86 architecture.
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* Note extra padding because this structure is passed back and forth
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* between kernel and user space.
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*
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* semid64_ds was originally meant to be architecture specific, but
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* everyone just ended up making identical copies without specific
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* optimizations, so we may just as well all use the same one.
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*
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* 64 bit architectures use a 64-bit __kernel_time_t here, while
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* 32 bit architectures have a pair of unsigned long values.
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* so they do not need the first two padding words.
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*
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* On big-endian systems, the padding is in the wrong place for
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* historic reasons, so user space has to reconstruct a time_t
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* value using
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*
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* user_semid_ds.sem_otime = kernel_semid64_ds.sem_otime +
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* ((long long)kernel_semid64_ds.sem_otime_high << 32)
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*
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* Pad space is left for 2 miscellaneous 32-bit values
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*/
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struct semid64_ds {
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struct ipc64_perm sem_perm; /* permissions .. see ipc.h */
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#if __BITS_PER_LONG == 64
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__kernel_time_t sem_otime; /* last semop time */
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__kernel_time_t sem_ctime; /* last change time */
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#else
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unsigned long sem_otime; /* last semop time */
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unsigned long sem_otime_high;
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unsigned long sem_ctime; /* last change time */
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unsigned long sem_ctime_high;
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#endif
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unsigned long sem_nsems; /* no. of semaphores in array */
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unsigned long __unused3;
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unsigned long __unused4;
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};
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#endif /* __ASM_GENERIC_SEMBUF_H */
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