Date: Wed, 5 Sep 2012 20:34:50 +0000 From: Alexander Best <arundel@freebsd.org> To: Eir Nym <eirnym@gmail.com> Cc: FreeBSD Mail Lists <freebsd-current@freebsd.org> Subject: Re: Are clang unsigned comparison warnings in kern/kern_* ok? Message-ID: <20120905203450.GA45200@freebsd.org> In-Reply-To: <CAO8GK0qXVGkaOByjRcn=ruSoBw6j%2Bj-hrMeDUjYRsFguCSpELw@mail.gmail.com> References: <CAO8GK0qXVGkaOByjRcn=ruSoBw6j%2Bj-hrMeDUjYRsFguCSpELw@mail.gmail.com>
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On Wed Sep 5 12, Eir Nym wrote: > I've got following warnings [no errors had been generated while > -Werror is in command line] and want to know if they are ok. There are > much more same warnings in modules, but I worry about kernel : > Kernel config: http://eroese.org/_/_/pub/bsd/240070/GENERIC_PF.amd64 > src.conf: http://eroese.org/_/_/pub/bsd/240070/src.conf > make.conf: /dev/null > kernel build logs: http://eroese.org/_/_/pub/bsd/240070/kernel.amd64.GENERIC_PF yes these are OK. clang complains about variables that were defined as unsigned, but are being compared against < 0. since those variables cannot be negative, comparing them against < 0 makes no sence (hence -Wtautological-compare as name to define this group of warnings). in theory calng is right, however in practice there might be good reasons to do so: 1) as a general safety belt to make programmers feel comfortable 2) the check might be there, because in the future it is being planed to switch a certain variable from unsigned to signed 3) a variable type might be unsigned on one platform per default (no signed or unsigned keyword used), but might be signed on another. doing the < 0 check prevents programmers from having to deal with both cases. you can disable these warnings for clang by setting -Wno-tautological-compare. no idea however what var to put it in. CWARNFLAGS+= in src.conf maybe. cheers. alex > > cc -c -O2 -pipe -fno-strict-aliasing -std=c99 -Wall > -Wredundant-decls -Wnested-externs -Wstrict-prototypes > -Wmissing-prototypes -Wpointer-arith -Winline -Wcast-qual -Wundef > -Wno-pointer-sign -fformat-extensions -Wmissing-include-dirs > -fdiagnostics-show-option -Wno-error-tautological-compare > -Wno-error-empty-body -Wno-error-parentheses-equality -nostdinc -I. > -I/usr/head/src/sys -I/usr/head/src/sys/contrib/altq -D_KERNEL > -DHAVE_KERNEL_OPTION_HEADERS -include opt_global.h > -fno-omit-frame-pointer -mno-aes -mno-avx -mcmodel=kernel > -mno-red-zone -mno-mmx -mno-sse -msoft-float > -fno-asynchronous-unwind-tables -ffreestanding -fstack-protector > -Werror /usr/head/src/sys/kern/kern_cpuset.c > /usr/head/src/sys/kern/kern_cpuset.c:654:16: warning: comparison of > unsigned expression < 0 is always false [-Wtautological-compare] > for (i = 0; i < (_NCPUWORDS - 1); i++) { > ~ ^ ~~~~~~~~~~~~~~~~ > 1 warning generated. > > /usr/head/src/sys/kern/kern_poll.c:173:10: warning: comparison of > unsigned expression < 0 is always false [-Wtautological-compare] > if (val < 0 || val > 99) > ~~~ ^ ~ > 1 warning generated. > > cc -c -O2 -pipe -fno-strict-aliasing -std=c99 -Wall > -Wredundant-decls -Wnested-externs -Wstrict-prototypes > -Wmissing-prototypes -Wpointer-arith -Winline -Wcast-qual -Wundef > -Wno-pointer-sign -fformat-extensions -Wmissing-include-dirs > -fdiagnostics-show-option -Wno-error-tautological-compare > -Wno-error-empty-body -Wno-error-parentheses-equality -nostdinc -I. > -I/usr/head/src/sys -I/usr/head/src/sys/contrib/altq -D_KERNEL > -DHAVE_KERNEL_OPTION_HEADERS -include opt_global.h > -fno-omit-frame-pointer -mno-aes -mno-avx -mcmodel=kernel > -mno-red-zone -mno-mmx -mno-sse -msoft-float > -fno-asynchronous-unwind-tables -ffreestanding -fstack-protector > -Werror /usr/head/src/sys/kern/kern_umtx.c > /usr/head/src/sys/kern/kern_umtx.c:3312:19: warning: comparison of > unsigned expression < 0 is always false [-Wtautological-compare] > if (ts32.tv_sec < 0 || > ~~~~~~~~~~~ ^ ~ > /usr/head/src/sys/kern/kern_umtx.c:3314:20: warning: comparison of > unsigned expression < 0 is always false [-Wtautological-compare] > ts32.tv_nsec < 0) > ~~~~~~~~~~~~ ^ ~ > /usr/head/src/sys/kern/kern_umtx.c:3338:25: warning: comparison of > unsigned expression < 0 is always false [-Wtautological-compare] > if (t32.timeout.tv_sec < 0 || > ~~~~~~~~~~~~~~~~~~ ^ ~ > /usr/head/src/sys/kern/kern_umtx.c:3339:63: warning: comparison of > unsigned expression < 0 is always false [-Wtautological-compare] > t32.timeout.tv_nsec >= 1000000000 || t32.timeout.tv_nsec < 0) > ~~~~~~~~~~~~~~~~~~~ ^ ~ > 4 warnings generated. > > > cc -c -O2 -pipe -fno-strict-aliasing -std=c99 -Wall > -Wredundant-decls -Wnested-externs -Wstrict-prototypes > -Wmissing-prototypes -Wpointer-arith -Winline -Wcast-qual -Wundef > -Wno-pointer-sign -fformat-extensions -Wmissing-include-dirs > -fdiagnostics-show-option -Wno-error-tautological-compare > -Wno-error-empty-body -Wno-error-parentheses-equality -nostdinc -I. > -I/usr/head/src/sys -I/usr/head/src/sys/contrib/altq -D_KERNEL > -DHAVE_KERNEL_OPTION_HEADERS -include opt_global.h > -fno-omit-frame-pointer -mno-aes -mno-avx -mcmodel=kernel > -mno-red-zone -mno-mmx -mno-sse -msoft-float > -fno-asynchronous-unwind-tables -ffreestanding -fstack-protector > -Werror /usr/head/src/sys/kern/uipc_syscalls.c > /usr/head/src/sys/kern/uipc_syscalls.c:356:16: warning: comparison of > unsigned expression < 0 is always false [-Wtautological-compare] > if (*namelen < 0) > ~~~~~~~~ ^ ~ > /usr/head/src/sys/kern/uipc_syscalls.c:1487:12: warning: comparison of > unsigned expression < 0 is always false [-Wtautological-compare] > if (*alen < 0) > ~~~~~ ^ ~ > /usr/head/src/sys/kern/uipc_syscalls.c:1587:12: warning: comparison of > unsigned expression < 0 is always false [-Wtautological-compare] > if (*alen < 0) > ~~~~~ ^ ~ > 3 warnings generated. > > -- Eir Nym
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