Commit-ID: 3578baaed4613a9fc09bab9f79f6ce2ac682e8a3
Gitweb: http://git.kernel.org/tip/3578baaed4613a9fc09bab9f79f6ce2ac682e8a3
Author: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
AuthorDate: Tue, 12 Feb 2013 11:47:31 -0800
Committer: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
CommitDate: Tue, 12 Feb 2013 12:46:40 -0800
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@xxxxxxxxxxxxx>
Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Russell King <linux@xxxxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: H. J. Lu <hjl.tools@xxxxxxxxx>
Link: http://lkml.kernel.org/r/511A8922.6050908@xxxxxxxxx
Signed-off-by: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
---
arch/x86/include/asm/uaccess.h | 57 +++++++++++-------------------------------
1 file changed, 14 insertions(+), 43 deletions(-)
diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index a8d1265..d710a25 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; \
})
--
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