diff options
| author | H. Peter Anvin <hpa@linux.intel.com> | 2013-02-12 11:47:31 -0800 |
|---|---|---|
| committer | H. Peter Anvin <hpa@linux.intel.com> | 2013-02-12 12:46:40 -0800 |
| commit | 3578baaed4613a9fc09bab9f79f6ce2ac682e8a3 (patch) | |
| tree | 2f58dbf5dcc6325fd87f17ccafd00f08bed741d8 /arch/x86/include/asm | |
| parent | 16640165c9079e2cf36fdcfca093f29663a716f7 (diff) | |
x86, mm: Redesign get_user with a __builtin_choose_expr hack
Instead of using a bitfield, use an odd little trick using typeof,
__builtin_choose_expr, and sizeof. __builtin_choose_expr is
explicitly defined to not convert its type (its argument is required
to be a constant expression) so this should be well-defined.
The code is still not 100% preturbation-free versus the baseline
before 64-bit get_user(), but the differences seem to be very small,
mostly related to padding and to gcc deciding when to spill registers.
Cc: Jamie Lokier <jamie@shareable.org>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: H. J. Lu <hjl.tools@gmail.com>
Link: http://lkml.kernel.org/r/511A8922.6050908@zytor.com
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Diffstat (limited to 'arch/x86/include/asm')
| -rw-r--r-- | arch/x86/include/asm/uaccess.h | 57 |
1 files changed, 14 insertions, 43 deletions
diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h index a8d12653f304..d710a2555fd6 100644 --- a/arch/x86/include/asm/uaccess.h +++ b/arch/x86/include/asm/uaccess.h @@ -125,13 +125,12 @@ extern int __get_user_4(void); extern int __get_user_8(void); extern int __get_user_bad(void); -#define __get_user_x(size, ret, x, ptr) \ - asm volatile("call __get_user_" #size \ - : "=a" (ret), "=d" (x) \ - : "0" (ptr)) \ - -/* Careful: we have to cast the result to the type of the pointer - * for sign reasons */ +/* + * This is a type: either unsigned long, if the argument fits into + * that type, or otherwise unsigned long long. + */ +#define __inttype(x) \ +__typeof__(__builtin_choose_expr(sizeof(x) > sizeof(0UL), 0ULL, 0UL)) /** * get_user: - Get a simple variable from user space. @@ -149,48 +148,20 @@ extern int __get_user_bad(void); * * Returns zero on success, or -EFAULT on error. * On error, the variable @x is set to zero. + * + * Careful: we have to cast the result to the type of the pointer + * for sign reasons. */ -#ifdef CONFIG_X86_32 -#define __get_user_8(ret, x, ptr) \ -do { \ - register unsigned long long __xx asm("%edx"); \ - asm volatile("call __get_user_8" \ - : "=a" (ret), "=r" (__xx) \ - : "0" (ptr)); \ - (x) = __xx; \ -} while (0) - -#else -#define __get_user_8(__ret_gu, __val_gu, ptr) \ - __get_user_x(8, __ret_gu, __val_gu, ptr) -#endif - #define get_user(x, ptr) \ ({ \ int __ret_gu; \ - struct { \ - unsigned long long __val_n : 8*sizeof(*(ptr)); \ - } __val_gu; \ + register __inttype(*(ptr)) __val_gu asm("%edx"); \ __chk_user_ptr(ptr); \ might_fault(); \ - switch (sizeof(*(ptr))) { \ - case 1: \ - __get_user_x(1, __ret_gu, __val_gu.__val_n, ptr); \ - break; \ - case 2: \ - __get_user_x(2, __ret_gu, __val_gu.__val_n, ptr); \ - break; \ - case 4: \ - __get_user_x(4, __ret_gu, __val_gu.__val_n, ptr); \ - break; \ - case 8: \ - __get_user_8(__ret_gu, __val_gu.__val_n, ptr); \ - break; \ - default: \ - __get_user_x(X, __ret_gu, __val_gu.__val_n, ptr); \ - break; \ - } \ - (x) = (__typeof__(*(ptr)))__val_gu.__val_n; \ + asm volatile("call __get_user_%P3" \ + : "=a" (__ret_gu), "=r" (__val_gu) \ + : "0" (ptr), "i" (sizeof(*(ptr)))); \ + (x) = (__typeof__(*(ptr))) __val_gu; \ __ret_gu; \ }) |