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ARC: syscall for userspace cmpxchg assist

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Older ARC700 cores (ARC750 specifically) lack instructions to implement
atomic r-w-w. This is problematic for userspace libraries such as NPTL
which need atomic primitives. So enable them by providing kernel assist.
This is costly but really the only sane soluton (othern than tight
spinning using the otherwise availiable atomic exchange EX instruciton).

Good thing is there are only a few of these cores running Linux out in
the wild.

This only works on UP systems.

Reviewed-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
This commit is contained in:
Vineet Gupta
2016-10-20 07:39:45 -07:00
parent 1dec785853
commit 91e040a79d
3 changed files with 39 additions and 4 deletions
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9
arch/arc/include/uapi/asm/unistd.h
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@@ -27,18 +27,19 @@
#define NR_syscalls __NR_syscalls
/* Generic syscall (fs/filesystems.c - lost in asm-generic/unistd.h */
#define __NR_sysfs (__NR_arch_specific_syscall + 3)
/* ARC specific syscall */
#define __NR_cacheflush (__NR_arch_specific_syscall + 0)
#define __NR_arc_settls (__NR_arch_specific_syscall + 1)
#define __NR_arc_gettls (__NR_arch_specific_syscall + 2)
#define __NR_arc_usr_cmpxchg (__NR_arch_specific_syscall + 4)
__SYSCALL(__NR_cacheflush, sys_cacheflush)
__SYSCALL(__NR_arc_settls, sys_arc_settls)
__SYSCALL(__NR_arc_gettls, sys_arc_gettls)
/* Generic syscall (fs/filesystems.c - lost in asm-generic/unistd.h */
#define __NR_sysfs (__NR_arch_specific_syscall + 3)
__SYSCALL(__NR_arc_usr_cmpxchg, sys_arc_usr_cmpxchg)
__SYSCALL(__NR_sysfs, sys_sysfs)
#undef __SYSCALL