# [PATCH] Avoid gcc compiler warning 3 messages from 2014-12-08 to 2014-12-09. Participants: Johannes Schindelin, Jeff King. Thread: https://gitlist.dev/t/38146 ## Johannes Schindelin, 2014-12-08 16:38 Subject: [PATCH] Avoid gcc compiler warning Message-ID: URL: https://gitlist.dev/e/b9e1cb1f858e71b964be4f752fcebc22cd944ebc.1418056722.git.johannes.schindelin%40gmx.de In-Reply-To: ``` At least on this developer's MacOSX (Snow Leopard, gcc-4.2.1), GCC prints a warning that 'hash' may be used uninitialized when compiling test-hashmap that 'hash' may be used uninitialized (but GCC 4.6.3 on this developer's Ubuntu server does not report this problem). Since hash() is called from perf_hashmap() which accepts an unchecked integer value from the command line, the warning appears to be legitimate, even if the test-hashmap command is only called from the test suite. Signed-off-by: Johannes Schindelin --- test-hashmap.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/test-hashmap.c b/test-hashmap.c index 07aa7ec..40a126d 100644 --- a/test-hashmap.c +++ b/test-hashmap.c @@ -62,6 +62,8 @@ static unsigned int hash(unsigned int method, unsigned int i, const char *key) case HASH_METHOD_0: hash = 0; break; + default: + die("Unknown method: %d", method); } if (method & HASH_METHOD_X2) -- 2.0.0.rc3.9669.g840d1f9 ``` ## Jeff King, 2014-12-09 08:47 Subject: Re: [PATCH] Avoid gcc compiler warning Message-ID: <20141209084728.GA13123@peff.net> URL: https://gitlist.dev/e/20141209084728.GA13123%40peff.net In-Reply-To: ``` On Mon, Dec 08, 2014 at 05:38:59PM +0100, Johannes Schindelin wrote: > At least on this developer's MacOSX (Snow Leopard, gcc-4.2.1), GCC prints > a warning that 'hash' may be used uninitialized when compiling > test-hashmap that 'hash' may be used uninitialized (but GCC 4.6.3 on this > developer's Ubuntu server does not report this problem). > > Since hash() is called from perf_hashmap() which accepts an unchecked > integer value from the command line, the warning appears to be legitimate, > even if the test-hashmap command is only called from the test suite. I think the older gcc is wrong; we are switching on "method & 3", which must be in the range 0-3 (and we cover all cases). I do not mind silencing the warning anyway, but see this discussion: http://thread.gmane.org/gmane.comp.version-control.git/258186 The thread seems very broken in gmane, but it continues here: http://article.gmane.org/gmane.comp.version-control.git/258232 http://thread.gmane.org/gmane.comp.version-control.git/258245 http://article.gmane.org/gmane.comp.version-control.git/258264 -Peff ``` ## Johannes Schindelin, 2014-12-09 09:48 Subject: Re: [PATCH] Avoid gcc compiler warning Message-ID: URL: https://gitlist.dev/e/alpine.DEB.1.00.1412091039130.13845%40s15462909.onlinehome-server.info In-Reply-To: <20141209084728.GA13123@peff.net> ``` Hi Peff, On Tue, 9 Dec 2014, Jeff King wrote: > On Mon, Dec 08, 2014 at 05:38:59PM +0100, Johannes Schindelin wrote: > > > At least on this developer's MacOSX (Snow Leopard, gcc-4.2.1), GCC prints > > a warning that 'hash' may be used uninitialized when compiling > > test-hashmap that 'hash' may be used uninitialized (but GCC 4.6.3 on this > > developer's Ubuntu server does not report this problem). > > > > Since hash() is called from perf_hashmap() which accepts an unchecked > > integer value from the command line, the warning appears to be legitimate, > > even if the test-hashmap command is only called from the test suite. > > I think the older gcc is wrong; Thanks for pointing to the older thread. It just happened to make it inconvenient to develop the rather huge fsck api topic branch I submitted yesterday because my vi kept jumping to test-hashmap.c because of that compiler warning (and as you know, not everybody has the luxury of being able to upgrade their gcc *cough* *Xcode* *cough* *Snow Leopard*). > we are switching on "method & 3", which must be in the range 0-3 (and we > cover all cases). That is of course correct, but still does not address the compiler warning. Junio, you said that you would prefer the useless initialization, so here goes: -- snipsnap -- Subject: [PATCH] Avoid gcc compiler warning At least on this developer's MacOSX (Snow Leopard, gcc-4.2.1), GCC prints a warning that 'hash' may be used uninitialized when compiling test-hashmap that 'hash' may be used uninitialized (but GCC 4.6.3 on this developer's Ubuntu server does not report this problem). The old compiler is wrong, of course, as the switch(method & 3) statement already handles all the possible cases, but that does not help in a scenario where it is hard or impossible to upgrade to a newer compiler (e.g. being stuck on an older MacOSX and having to rely on Xcode). So let's just initialize the variable and be done with it, it is hardly a crucial part of the code because it is only used by the test suite and invisible to the end users. Signed-off-by: Johannes Schindelin --- test-hashmap.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/test-hashmap.c b/test-hashmap.c index 07aa7ec..cc2891d 100644 --- a/test-hashmap.c +++ b/test-hashmap.c @@ -47,7 +47,7 @@ static struct test_entry *alloc_test_entry(int hash, char *key, int klen, static unsigned int hash(unsigned int method, unsigned int i, const char *key) { - unsigned int hash; + unsigned int hash = 0; switch (method & 3) { case HASH_METHOD_FNV: -- 2.0.0.rc3.9669.g840d1f9 ```