Messages in this thread | | | Date | Fri, 15 Jul 2022 15:03:37 -0700 | From | Nathan Chancellor <> | Subject | Re: GCC fails to spot uninitialized variable |
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On Fri, Jul 15, 2022 at 11:09:17PM +0300, Petko Manolov wrote: > Guys, > > Today i was bitten by a stupid bug that i introduced myself while writing some > v4l2 code. Looking at it a bit more carefully i was surprised that GCC didn't > catch this one, as it was something that should definitely emit a warning. > > When included into the driver, this particular code: > > int blah(int a, int *b) > { > int ret; > > switch (a) { > case 0: > ret = a; > break; > case 1: > ret = *b; > break; > case 2: > *b = a; > break; > default: > ret = 0; > } > > return ret; > } > > somehow managed to defeat GCC checks. Compiling it as a standalone .c file > with: > > gcc -Wall -O2 -c t.c > > gives me nice: > > t.c:19:16: warning: 'ret' may be used uninitialized in this function [-Wmaybe-uninitialized] > 19 | return ret; > | ^~~ > > Any idea what might have gone wrong?
See commit 78a5255ffb6a ("Stop the ad-hoc games with -Wno-maybe-initialized") in 5.7, which disabled that warning for a default kernel build. You have to either include 'W=2' (which will introduce other warnings which might be noisy) or 'KCFLAGS=-Wmaybe-uninitialized' (which will just add that warning) in your make command to see those warnings.
As an aside, your mailer adds a "Mail-Followup-To:" header that was set to LKML, meaning that you would not have seen this reply unless you were subscribed to LKML. Might be something worth looking into.
Cheers, Nathan
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