[PATCH v2] cache.h: work around broken NetBSD system headers

Wrap the `mode' argument to the `canon_mode' macro in extra
parentheses to avoid a bug with the S_* macros in sys/stat.h on
NetBSD.

This issue was originally spotted in NetBSD Problem Report #42168 and
worked around by der Mouse, but later filed as a bug with NetBSD
itself in NetBSD Problem Report #43937 by me.

The issue is that NetBSD doesn't take care to wrap its macro arguments
in parentheses, so on Linux and other sane systems we have S_ISREG(m)
defined as something like:

    (((m) & S_IFMT) == S_IFREG)

But on NetBSD:

    ((m & _S_IFMT) == _S_IFREG)

Since a caller in builtin/diff.c called our macro as `S_IFREG | 0644'
this bug introduced a logic error on NetBSD, since the precedence of
bit-wise & is higher than | in C.

NetBSD-PR: http://gnats.netbsd.org/cgi-bin/query-pr-single.pl?number=43937
Originally-reported-by: der Mouse [off-list ref]
Signed-off-by: Ævar Arnfjörð Bjarmason <redacted>
---

On Mon, Oct 4, 2010 at 17:54, Junio C Hamano [off-list ref] wrote:

instead of contaminating the calling sites.  Otherwise new calling sites
we will add in the future need to be aware of the same bug for no good
reason.

Agreed. Here's a v2 that does that. With an updated commit message to
mention the bug I filed with NetBSD.

 cache.h |   10 ++++++++--
 1 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/cache.h b/cache.h
index 2ef2fa3..891d5d0 100644
--- a/cache.h
+++ b/cache.h

@@ -277,9 +277,15 @@ static inline int ce_to_dtype(const struct cache_entry *ce)
 	else
 		return DT_UNKNOWN;
 }
+
+/*
+ * We use extra parentheses around mode to work around a NetBSD issue
+ * described in NetBSD Problem Report #43937. See
+ * http://www.netbsd.org/cgi-bin/query-pr-single.pl?number=43937
+ */
 #define canon_mode(mode) \
-	(S_ISREG(mode) ? (S_IFREG | ce_permissions(mode)) : \
-	S_ISLNK(mode) ? S_IFLNK : S_ISDIR(mode) ? S_IFDIR : S_IFGITLINK)
+	(S_ISREG((mode)) ? (S_IFREG | ce_permissions(mode)) : \
+	S_ISLNK((mode)) ? S_IFLNK : S_ISDIR((mode)) ? S_IFDIR : S_IFGITLINK)
 
 #define flexible_size(STRUCT,len) ((offsetof(struct STRUCT,name) + (len) + 8) & ~7)
 #define cache_entry_size(len) flexible_size(cache_entry,len)

-- 
1.7.3.159.g610493