On Wed, 9 Oct 2019 23:45:02 +0200 Rikard Falkeborn <rikard.falkeb...@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" }, ^~~~~~~