Re: [notmuch] [PATCH 1/2] * avoid gcc 4.4.1 compiler warnings due to ignored write...

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+From: Carl Worth <cworth@cworth.org>\r
+To: Jed Brown <jed@59A2.org>, Karl Wiberg <kha@treskal.com>,\r
+       Dirk-Jan Binnema <djcb.bulk@gmail.com>\r
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+Date: Tue, 01 Dec 2009 07:57:30 -0800\r
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+Cc: "notmuch@notmuchmail org" <notmuch@notmuchmail.org>, djcb@djcbsoftware.nl\r
+Subject: Re: [notmuch] [PATCH 1/2] * avoid gcc 4.4.1 compiler warnings due\r
+ to ignored write return values\r
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+--=-=-=\r
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+On Mon, 23 Nov 2009 15:24:46 +0100, Jed Brown <jed@59A2.org> wrote:\r
+> >From the gcc man page:\r
+>=20\r
+>        -Wunused-value\r
+>            Warn whenever a statement computes a result that is explicitly\r
+>            not used. To suppress this warning cast the unused expression\r
+>            to void. This includes an expression-statement or the left-\r
+>            hand side of a comma expression that contains no side effects.\r
+>            For example, an expression such as x[i,j] will cause a\r
+>            warning, while x[(void)i,j] will not.\r
+>=20\r
+>            This warning is enabled by -Wall.\r
+>=20\r
+> But I'm confused here because I don't currently see any warnings with\r
+> gcc-4.4.2.  Actually this must be a bug because I get no warnings for\r
+> the blatantly unused\r
+>=20\r
+>   malloc(5);\r
+\r
+I'm guessing that the -Wunused-value warning doesn't consider values\r
+computed by function calls.\r
+\r
+> with -Wall -Wextra -pedantic.  Anyway, if your system headers specify\r
+> __attribute__((warn_unused_result)) for write, then you could be running\r
+> into this bug/feature\r
+>=20\r
+>   http://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D35579\r
+\r
+Yes, this is the attribute that's triggering the warnings. I poked\r
+around in the glibc headers to see how to get this warning myself, and I\r
+finally found:\r
+\r
+       make CFLAGS=3D"-O -D_FORTIFY_SOURCE"\r
+\r
+That makes the warning appear even with gcc 4.3.4, (and the definitions\r
+in the headers suggest it will work with any gcc >=3D 4.1).\r
+\r
+So I've pushed the patch now, (with an updated commit message to reflect\r
+the above analysis).\r
+\r
+=2DCarl\r
+\r
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