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SubjectRe: linux-next: Tree for Dec 6 (objtool, lots in btrfs)
On Tue, Dec 17, 2019 at 04:29:54PM +0100, David Sterba wrote:
> Separating the definitions by #ifdef looks ok, I'd rather do separate
> definitions of ASSERT too, to avoid the ternary operator. I'll send the
> patch.

Subject: [PATCH] btrfs: separate definition of assertion failure handlers

There's a report where objtool detects unreachable instructions, eg.:

fs/btrfs/ctree.o: warning: objtool: btrfs_search_slot()+0x2d4: unreachable instruction

This seems to be a false positive due to compiler version. The cause is
in the ASSERT macro implementation that does the conditional check as
IS_DEFINED(CONFIG_BTRFS_ASSERT) and not an #ifdef.

To avoid that, use the ifdefs directly.

CC: Josh Poimboeuf <jpoimboe@redhat.com>
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: David Sterba <dsterba@suse.com>
---
fs/btrfs/ctree.h | 20 ++++++++++++--------
1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 569931dd0ce5..f90b82050d2d 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -3157,17 +3157,21 @@ do { \
rcu_read_unlock(); \
} while (0)

-__cold
-static inline void assfail(const char *expr, const char *file, int line)
+#ifdef CONFIG_BTRFS_ASSERT
+__cold __noreturn
+static inline void assertfail(const char *expr, const char *file, int line)
{
- if (IS_ENABLED(CONFIG_BTRFS_ASSERT)) {
- pr_err("assertion failed: %s, in %s:%d\n", expr, file, line);
- BUG();
- }
+ pr_err("assertion failed: %s, in %s:%d\n", expr, file, line);
+ BUG();
}

-#define ASSERT(expr) \
- (likely(expr) ? (void)0 : assfail(#expr, __FILE__, __LINE__))
+#define ASSERT(expr) \
+ (likely(expr) ? (void)0 : assertfail(#expr, __FILE__, __LINE__))
+
+#else
+static inline void assertfail(const char *expr, const char* file, int line) { }
+#define ASSERT(expr) (void)(expr)
+#endif

/*
* Use that for functions that are conditionally exported for sanity tests but
--
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