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authorRichard Henderson <rth@twiddle.net>2013-01-04 16:39:31 -0800
committerBlue Swirl <blauwirbel@gmail.com>2013-01-12 12:24:47 +0000
commit658f2dc970996d547a641b5685e384ebe6f2648e (patch)
treec88fc8c6d516caac5942676f65bcb7cb1f5788ff /linux-user
parentc732a52d3e3b7ed42d7daa94ba40a83408cd6f22 (diff)
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linux-user: Rewrite __get_user/__put_user with __builtin_choose_expr
The previous formuation with multiple assignments to __typeof(*hptr) falls down when hptr is qualified const. E.g. with const struct S *p, p->f is also qualified const. With this formulation, there's no assignment to any local variable. Signed-off-by: Richard Henderson <rth@twiddle.net> Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
Diffstat (limited to 'linux-user')
-rw-r--r--linux-user/qemu.h63
1 files changed, 33 insertions, 30 deletions
diff --git a/linux-user/qemu.h b/linux-user/qemu.h
index 8a3538c..31a220a 100644
--- a/linux-user/qemu.h
+++ b/linux-user/qemu.h
@@ -287,36 +287,39 @@ static inline int access_ok(int type, abi_ulong addr, abi_ulong size)
(type == VERIFY_READ) ? PAGE_READ : (PAGE_READ | PAGE_WRITE)) == 0;
}
-/* NOTE __get_user and __put_user use host pointers and don't check access. */
-/* These are usually used to access struct data members once the
- * struct has been locked - usually with lock_user_struct().
- */
-#define __put_user(x, hptr)\
-({ __typeof(*hptr) pu_ = (x);\
- switch(sizeof(*hptr)) {\
- case 1: break;\
- case 2: pu_ = tswap16(pu_); break; \
- case 4: pu_ = tswap32(pu_); break; \
- case 8: pu_ = tswap64(pu_); break; \
- default: abort();\
- }\
- memcpy(hptr, &pu_, sizeof(pu_)); \
- 0;\
-})
-
-#define __get_user(x, hptr) \
-({ __typeof(*hptr) gu_; \
- memcpy(&gu_, hptr, sizeof(gu_)); \
- switch(sizeof(*hptr)) {\
- case 1: break; \
- case 2: gu_ = tswap16(gu_); break; \
- case 4: gu_ = tswap32(gu_); break; \
- case 8: gu_ = tswap64(gu_); break; \
- default: abort();\
- }\
- (x) = gu_; \
- 0;\
-})
+/* NOTE __get_user and __put_user use host pointers and don't check access.
+ These are usually used to access struct data members once the struct has
+ been locked - usually with lock_user_struct. */
+
+/* Tricky points:
+ - Use __builtin_choose_expr to avoid type promotion from ?:,
+ - Invalid sizes result in a compile time error stemming from
+ the fact that abort has no parameters.
+ - It's easier to use the endian-specific unaligned load/store
+ functions than host-endian unaligned load/store plus tswapN. */
+
+#define __put_user_e(x, hptr, e) \
+ (__builtin_choose_expr(sizeof(*(hptr)) == 1, stb_p, \
+ __builtin_choose_expr(sizeof(*(hptr)) == 2, stw_##e##_p, \
+ __builtin_choose_expr(sizeof(*(hptr)) == 4, stl_##e##_p, \
+ __builtin_choose_expr(sizeof(*(hptr)) == 8, stq_##e##_p, abort)))) \
+ ((hptr), (x)), 0)
+
+#define __get_user_e(x, hptr, e) \
+ ((x) = \
+ __builtin_choose_expr(sizeof(*(hptr)) == 1, ldub_p, \
+ __builtin_choose_expr(sizeof(*(hptr)) == 2, lduw_##e##_p, \
+ __builtin_choose_expr(sizeof(*(hptr)) == 4, ldl_##e##_p, \
+ __builtin_choose_expr(sizeof(*(hptr)) == 8, ldq_##e##_p, abort)))) \
+ (hptr), 0)
+
+#ifdef TARGET_WORDS_BIGENDIAN
+# define __put_user(x, hptr) __put_user_e(x, hptr, be)
+# define __get_user(x, hptr) __get_user_e(x, hptr, be)
+#else
+# define __put_user(x, hptr) __put_user_e(x, hptr, le)
+# define __get_user(x, hptr) __get_user_e(x, hptr, le)
+#endif
/* put_user()/get_user() take a guest address and check access */
/* These are usually used to access an atomic data type, such as an int,