Date: Tue, 8 Nov 2011 00:12:47 +0000 From: Alexander Best <arundel@freebsd.org> To: Adrian Chadd <adrian@freebsd.org> Cc: freebsd-toolchain@freebsd.org, Dimitry Andric <dim@freebsd.org> Subject: Re: state of clang(1)'s -Wshift-count-negative and -Wshift-overflow warnings Message-ID: <20111108001247.GA88837@freebsd.org> In-Reply-To: <CAJ-VmoniRVx35M%2Be0baXVLj0Gxx_nok1XPc4n5ewLYNzNASFGQ@mail.gmail.com> References: <20111103104523.GA30132@freebsd.org> <4EB2AF08.9010806@FreeBSD.org> <20111103190312.GA6709@freebsd.org> <4EB2F4CE.8050806@FreeBSD.org> <CAJ-VmoniRVx35M%2Be0baXVLj0Gxx_nok1XPc4n5ewLYNzNASFGQ@mail.gmail.com>
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On Thu Nov 3 11, Adrian Chadd wrote: > Hi, > > Please submit a PR and I'll fix the AR5210 code. I'll have to find an > AR5210 though to test it against though... filed under kern/162366 and assigned to you. ;) cheers. alex > > > Adrian > > On 3 November 2011 13:08, Dimitry Andric <dim@freebsd.org> wrote: > > On 2011-11-03 20:03, Alexander Best wrote: > >> On Thu Nov 3 11, Dimitry Andric wrote: > >>> On 2011-11-03 11:45, Alexander Best wrote: > >>> ... > >>>> /usr/git-freebsd-head/sys/dev/ath/ath_hal/ar5210/ar5210_power.c:36:3: warning: signed shift result (0x200000000) requires 35 bits to represent, but 'int' only has 32 bits [-Wshift-overflow] > >>>> OS_REG_RMW_FIELD(ah, AR_SCR, AR_SCR_SLE, AR_SCR_SLE_ALLOW); > >>>> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > >>>> /usr/git-freebsd-head/sys/dev/ath/ath_hal/ah_internal.h:471:42: note: expanded from macro 'OS_REG_RMW_FIELD' > >>>> (OS_REG_READ(_a, _r) &~ (_f)) | (((_v) << _f##_S) & (_f))) > >>>> ^ > >>>> /usr/git-freebsd-head/sys/dev/ath/ah_osdep.h:127:49: note: expanded from macro 'OS_REG_WRITE' > >>>> (bus_space_handle_t)(_ah)->ah_sh, (_reg), (_val)) > > ... > >>> Those warnings are bogus, and due to this bug: > > > > Actually, I was too quick with this one, since it isn't bogus. The > > macro invocation: > > > > OS_REG_RMW_FIELD(ah, AR_SCR, AR_SCR_SLE, AR_SCR_SLE_ALLOW); > > > > ultimately expands to: > > > > bus_space_write_4((bus_space_tag_t)(ah)->ah_st, (bus_space_handle_t)(ah)->ah_sh, (0x4004), ((bus_space_read_4((bus_space_tag_t)(ah)->ah_st, (bus_space_handle_t)(ah)->ah_sh, (0x4004)) &~ (0x00030000)) | (((0x00020000) << 16) & (0x00030000)))); > > > > The problem part is ((0x00020000) << 16), which is an overflow. I'm not > > sure how clang concludes that the result (0x200000000) needs 35 bits to > > represent, as it seems to use 34 bits to me. But that it doesn't fit > > into a signed integer is crystal-clear. > > > > E.g. this is a real bug! Probably something in the macro needs to > > explicitly cast to 64 integers, or another workaround must be found. > > > > The other warning: > > > >> In file included from /usr/git-freebsd-head/sys/dev/ath/ath_hal/ah_regdomain.c:99: > >> /usr/git-freebsd-head/sys/dev/ath/ath_hal/ah_regdomain/ah_rd_domains.h:69:15: warning: shift count is negative [-Wshift-count-negative] > >> .chan11a = BM4(F1_4950_4980, > >> ^~~~~~~~~~~~~~~~~ > >> /usr/git-freebsd-head/sys/dev/ath/ath_hal/ah_regdomain/ah_rd_domains.h:41:4: note: expanded from macro 'BM4' > >> W1(_fa) | W1(_fb) | W1(_fc) | W1(_fd) } > >> ^ > >> /usr/git-freebsd-head/sys/dev/ath/ath_hal/ah_regdomain/ah_rd_domains.h:34:45: note: expanded from macro 'W1' > >> (((_a) > 63 && (_a) < 128 ? (((uint64_t) 1)<<((_a)-64)) : (uint64_t) 0)) > >> ^ ~~~~~~~~~ > > > > is indeed bogus, since the macro makes sure the shift count never > > becomes negative. (N.B.: This only happens for global initializations, > > *not* if you would use the same macro in a function.) > > > > > >>> http://llvm.org/bugs/show_bug.cgi?id=10030 > >>> > >>> Unfortunately, it is still not fixed for the 3.0 release branch, and I > >>> don't expect it will be fixed for the actual release. > >> > >> thanks for the info. so how about something like > >> > >> diff --git a/sys/conf/kern.mk b/sys/conf/kern.mk > >> index a0a595f..3cb13de 100644 > >> --- a/sys/conf/kern.mk > >> +++ b/sys/conf/kern.mk > >> @@ -1,12 +1,28 @@ > >> # $FreeBSD$ > >> > >> # > >> -# Warning flags for compiling the kernel and components of the kernel: > >> +# XXX Disable bogus llvm warnings, complaining about perfectly valid shifts. > >> +# See http://llvm.org/bugs/show_bug.cgi?id=10030 for more details. > >> +# > >> +.if ${CC:T:Mclang} == "clang" > >> +NOSHIFTWARNS= -Wno-shift-count-negative -Wno-shift-count-overflow \ > >> + -Wno-shift-overflow > >> +.endif > >> + > >> > >> ...and then add ${NOSHIFTWARNS} to the end of CWARNFLAGS? > > > > No, this is a way too big hammer, because it eliminates the useful > > warnings together with the false positives. > > > > It would be better to only apply this band-aid for the specific source > > files that need it, and even then, I would rather wait for the proper > > fix from upstream. > >
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