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Subject[PATCH] kmemcheck: make bitfield annotations truly no-ops when disabled
Date
It turns out that even zero-sized struct members (int foo[0];) will affect
the struct layout, causing us in particular to lose 4 bytes in struct sock.

This patch fixes the regression in CONFIG_KMEMCHECK=n case.

Reported-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Vegard Nossum <vegard.nossum@gmail.com>
---
include/linux/kmemcheck.h | 110 ++++++++++++++++++++++++---------------------
1 files changed, 58 insertions(+), 52 deletions(-)

Andrew: Compile tested on x86_32 and x86_64, but because of my bad track
record when it comes to brown paper bugs, can you please keep this in -mm
for a little while? Thanks.

diff --git a/include/linux/kmemcheck.h b/include/linux/kmemcheck.h
index e880d4c..08d7dc4 100644
--- a/include/linux/kmemcheck.h
+++ b/include/linux/kmemcheck.h
@@ -36,6 +36,56 @@ int kmemcheck_hide_addr(unsigned long address);

bool kmemcheck_is_obj_initialized(unsigned long addr, size_t size);

+/*
+ * Bitfield annotations
+ *
+ * How to use: If you have a struct using bitfields, for example
+ *
+ * struct a {
+ * int x:8, y:8;
+ * };
+ *
+ * then this should be rewritten as
+ *
+ * struct a {
+ * kmemcheck_bitfield_begin(flags);
+ * int x:8, y:8;
+ * kmemcheck_bitfield_end(flags);
+ * };
+ *
+ * Now the "flags_begin" and "flags_end" members may be used to refer to the
+ * beginning and end, respectively, of the bitfield (and things like
+ * &x.flags_begin is allowed). As soon as the struct is allocated, the bit-
+ * fields should be annotated:
+ *
+ * struct a *a = kmalloc(sizeof(struct a), GFP_KERNEL);
+ * kmemcheck_annotate_bitfield(a, flags);
+ */
+#define kmemcheck_bitfield_begin(name) \
+ int name##_begin[0];
+
+#define kmemcheck_bitfield_end(name) \
+ int name##_end[0];
+
+#define kmemcheck_annotate_bitfield(ptr, name) \
+ do { \
+ int _n; \
+ \
+ if (!ptr) \
+ break; \
+ \
+ _n = (long) &((ptr)->name##_end) \
+ - (long) &((ptr)->name##_begin); \
+ MAYBE_BUILD_BUG_ON(_n < 0); \
+ \
+ kmemcheck_mark_initialized(&((ptr)->name##_begin), _n); \
+ } while (0)
+
+#define kmemcheck_annotate_variable(var) \
+ do { \
+ kmemcheck_mark_initialized(&(var), sizeof(var)); \
+ } while (0) \
+
#else
#define kmemcheck_enabled 0

@@ -106,60 +156,16 @@ static inline bool kmemcheck_is_obj_initialized(unsigned long addr, size_t size)
return true;
}

-#endif /* CONFIG_KMEMCHECK */
-
-/*
- * Bitfield annotations
- *
- * How to use: If you have a struct using bitfields, for example
- *
- * struct a {
- * int x:8, y:8;
- * };
- *
- * then this should be rewritten as
- *
- * struct a {
- * kmemcheck_bitfield_begin(flags);
- * int x:8, y:8;
- * kmemcheck_bitfield_end(flags);
- * };
- *
- * Now the "flags_begin" and "flags_end" members may be used to refer to the
- * beginning and end, respectively, of the bitfield (and things like
- * &x.flags_begin is allowed). As soon as the struct is allocated, the bit-
- * fields should be annotated:
- *
- * struct a *a = kmalloc(sizeof(struct a), GFP_KERNEL);
- * kmemcheck_annotate_bitfield(a, flags);
- *
- * Note: We provide the same definitions for both kmemcheck and non-
- * kmemcheck kernels. This makes it harder to introduce accidental errors. It
- * is also allowed to pass NULL pointers to kmemcheck_annotate_bitfield().
- */
-#define kmemcheck_bitfield_begin(name) \
- int name##_begin[0];
-
-#define kmemcheck_bitfield_end(name) \
- int name##_end[0];
+#define kmemcheck_bitfield_begin(name)
+#define kmemcheck_bitfield_end(name)
+#define kmemcheck_annotate_bitfield(ptr, name) \
+ do { \
+ } while (0)

-#define kmemcheck_annotate_bitfield(ptr, name) \
- do { \
- int _n; \
- \
- if (!ptr) \
- break; \
- \
- _n = (long) &((ptr)->name##_end) \
- - (long) &((ptr)->name##_begin); \
- MAYBE_BUILD_BUG_ON(_n < 0); \
- \
- kmemcheck_mark_initialized(&((ptr)->name##_begin), _n); \
+#define kmemcheck_annotate_variable(var) \
+ do { \
} while (0)

-#define kmemcheck_annotate_variable(var) \
- do { \
- kmemcheck_mark_initialized(&(var), sizeof(var)); \
- } while (0) \
+#endif /* CONFIG_KMEMCHECK */

#endif /* LINUX_KMEMCHECK_H */
--
1.6.0.6


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