Messages in this thread | | | From | Rikard Falkeborn <> | Date | Tue, 22 Oct 2019 21:53:06 +0200 | Subject | Re: [Patch v4 2/2] linux/bits.h: Add compile time sanity check of GENMASK inputs |
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On Fri, Oct 11, 2019 at 07:27:37PM -0700, Andrew Morton wrote: > On Wed, 9 Oct 2019 23:45:02 +0200 Rikard Falkeborn <rikard.falkeborn@gmail.com> wrote: > > > GENMASK() and GENMASK_ULL() are supposed to be called with the high bit > > as the first argument and the low bit as the second argument. Mixing > > them will return a mask with zero bits set. > > > > Recent commits show getting this wrong is not uncommon, see e.g. > > commit aa4c0c9091b0 ("net: stmmac: Fix misuses of GENMASK macro") and > > commit 9bdd7bb3a844 ("clocksource/drivers/npcm: Fix misuse of GENMASK > > macro"). > > > > To prevent such mistakes from appearing again, add compile time sanity > > checking to the arguments of GENMASK() and GENMASK_ULL(). If both > > arguments are known at compile time, and the low bit is higher than the > > high bit, break the build to detect the mistake immediately. > > > > Since GENMASK() is used in declarations, BUILD_BUG_ON_ZERO() must be > > used instead of BUILD_BUG_ON(). > > > > __builtin_constant_p does not evaluate is argument, it only checks if it > > is a constant or not at compile time, and __builtin_choose_expr does not > > evaluate the expression that is not chosen. Therefore, GENMASK(x++, 0) > > does only evaluate x++ once. > > > > Commit 95b980d62d52 ("linux/bits.h: make BIT(), GENMASK(), and friends > > available in assembly") made the macros in linux/bits.h available in > > assembly. Since BUILD_BUG_OR_ZERO() is not asm compatible, disable the > > checks if the file is included in an asm file. > > > > Due to bugs in GCC versions before 4.9 [0], disable the check if > > building with a too old GCC compiler. > > > > [0]: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=19449 > > I'm seeing some breakage in code which is newly added in linux-next: > > sound/soc/codecs/tas2562.c: In function tas2562_set_dai_tdm_slot: > ./include/linux/build_bug.h:16:51: error: negative width in bit-field <anonymous> > #define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); }))) > ^ > ./include/linux/bits.h:25:3: note: in expansion of macro BUILD_BUG_ON_ZERO > (BUILD_BUG_ON_ZERO(__builtin_choose_expr( \ > ^~~~~~~~~~~~~~~~~ > ./include/linux/bits.h:39:3: note: in expansion of macro GENMASK_INPUT_CHECK > (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l)) > ^~~~~~~~~~~~~~~~~~~ > sound/soc/codecs/tas2562.h:65:37: note: in expansion of macro GENMASK > #define TAS2562_TDM_CFG2_RXLEN_MASK GENMASK(0, 1) > ^~~~~~~ > sound/soc/codecs/tas2562.c:160:11: note: in expansion of macro TAS2562_TDM_CFG2_RXLEN_MASK > TAS2562_TDM_CFG2_RXLEN_MASK, > ^~~~~~~~~~~~~~~~~~~~~~~~~~~ > ./include/linux/build_bug.h:16:51: error: negative width in bit-field <anonymous> > #define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); }))) > ^ > ./include/linux/bits.h:25:3: note: in expansion of macro BUILD_BUG_ON_ZERO > (BUILD_BUG_ON_ZERO(__builtin_choose_expr( \ > > > and > > In file included from ./include/linux/bits.h:23:0, > from ./include/linux/ioport.h:15, > from ./include/linux/acpi.h:12, > from drivers/crypto/hisilicon/hpre/hpre_main.c:3: > ./include/linux/build_bug.h:16:51: error: negative width in bit-field ‘<anonymous>’ > #define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); }))) > ^ > ./include/linux/bits.h:25:3: note: in expansion of macro ‘BUILD_BUG_ON_ZERO’ > (BUILD_BUG_ON_ZERO(__builtin_choose_expr( \ > ^~~~~~~~~~~~~~~~~ > ./include/linux/bits.h:39:3: note: in expansion of macro ‘GENMASK_INPUT_CHECK’ > (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l)) > ^~~~~~~~~~~~~~~~~~~ > drivers/crypto/hisilicon/hpre/hpre_main.c:119:15: note: in expansion of macro ‘GENMASK’ > { .int_msk = GENMASK(10, 15), .msg = "hpre_ooo_rdrsp_err" }, > ^~~~~~~ > ./include/linux/build_bug.h:16:51: error: negative width in bit-field ‘<anonymous>’ > #define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); }))) > ^ > ./include/linux/bits.h:25:3: note: in expansion of macro ‘BUILD_BUG_ON_ZERO’ > (BUILD_BUG_ON_ZERO(__builtin_choose_expr( \ > ^~~~~~~~~~~~~~~~~ > ./include/linux/bits.h:39:3: note: in expansion of macro ‘GENMASK_INPUT_CHECK’ > (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l)) > ^~~~~~~~~~~~~~~~~~~ > drivers/crypto/hisilicon/hpre/hpre_main.c:120:15: note: in expansion of macro ‘GENMASK’ > { .int_msk = GENMASK(16, 21), .msg = "hpre_ooo_wrrsp_err" }, > ^~~~~~~ >
As of next-20191021, those breakages are fixed ([0], [1]). next-20191021 now builds (at least for x86-64) with the GENMASK compile checks added.
I also stumbled upon [2], which is a fix for an unused macro in a header in mips/include/asm. next-201008 contained both v3 of this patch and the mips header with the bad GENMASK in without build regressions, so it *should* be ok to include v4 (but given the track record of this patch, I totally understand if you want to wait until [2] lands in mips-next and linux-next).
Rikard
[0]: https://lore.kernel.org/patchwork/patch/1139777/ [1]: https://lore.kernel.org/patchwork/patch/1139778/ [2]: https://lore.kernel.org/linux-mips/20191022192547.480095-1-rikard.falkeborn@gmail.com/T/#u
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