# git rev-parse -q --verify d936eb23874433caa3e3d841cfa16f5434b85dcf^{commit} d936eb23874433caa3e3d841cfa16f5434b85dcf already have revision, skipping fetch # git checkout -q -f -B kisskb d936eb23874433caa3e3d841cfa16f5434b85dcf # git clean -qxdf # < git log -1 # commit d936eb23874433caa3e3d841cfa16f5434b85dcf # Author: Linus Torvalds # Date: Thu Jul 15 18:05:31 2021 -0700 # # Revert "Makefile: Enable -Wimplicit-fallthrough for Clang" # # This reverts commit b7eb335e26a9c7f258c96b3962c283c379d3ede0. # # It turns out that the problem with the clang -Wimplicit-fallthrough # warning is not about the kernel source code, but about clang itself, and # that the warning is unusable until clang fixes its broken ways. # # In particular, when you enable this warning for clang, you not only get # warnings about implicit fallthroughs. You also get this: # # warning: fallthrough annotation in unreachable code [-Wimplicit-fallthrough] # # which is completely broken becasue it # # (a) doesn't even tell you where the problem is (seriously: no line # numbers, no filename, no nothing). # # (b) is fundamentally broken anyway, because there are perfectly valid # reasons to have a fallthrough statement even if it turns out that # it can perhaps not be reached. # # In the kernel, an example of that second case is code in the scheduler: # # switch (state) { # case cpuset: # if (IS_ENABLED(CONFIG_CPUSETS)) { # cpuset_cpus_allowed_fallback(p); # state = possible; # break; # } # fallthrough; # case possible: # # where if CONFIG_CPUSETS is enabled you actually never hit the # fallthrough case at all. But that in no way makes the fallthrough # wrong. # # So the warning is completely broken, and enabling it for clang is a very # bad idea. # # In the meantime, we can keep the gcc option enabled, and make the gcc # build use # # -Wimplicit-fallthrough=5 # # which means that we will at least continue to require a proper # fallthrough statement, and that gcc won't silently accept the magic # comment versions. Because gcc does this all correctly, and while the odd # "=5" part is kind of obscure, it's documented in [1]: # # "-Wimplicit-fallthrough=5 doesn’t recognize any comments as # fallthrough comments, only attributes disable the warning" # # so if clang ever fixes its bad behavior we can try enabling it there again. # # Link: https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html [1] # Cc: Kees Cook # Cc: Gustavo A. R. Silva # Cc: Nathan Chancellor # Cc: Nick Desaulniers # Signed-off-by: Linus Torvalds # < /opt/cross/kisskb/korg/gcc-8.1.0-nolibc/s390-linux/bin/s390-linux-gcc --version # < /opt/cross/kisskb/korg/gcc-8.1.0-nolibc/s390-linux/bin/s390-linux-ld --version # < git log --format=%s --max-count=1 d936eb23874433caa3e3d841cfa16f5434b85dcf # < make -s -j 48 ARCH=s390 O=/kisskb/build/linus_s390-allmodconfig_s390x-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.1.0-nolibc/s390-linux/bin/s390-linux- allmodconfig # Added to kconfig CONFIG_BUILD_DOCSRC=n # Added to kconfig CONFIG_MODULE_SIG=n # Added to kconfig CONFIG_SAMPLES=n # < make -s -j 48 ARCH=s390 O=/kisskb/build/linus_s390-allmodconfig_s390x-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.1.0-nolibc/s390-linux/bin/s390-linux- help # make -s -j 48 ARCH=s390 O=/kisskb/build/linus_s390-allmodconfig_s390x-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.1.0-nolibc/s390-linux/bin/s390-linux- olddefconfig # make -s -j 48 ARCH=s390 O=/kisskb/build/linus_s390-allmodconfig_s390x-gcc8 CROSS_COMPILE=/opt/cross/kisskb/korg/gcc-8.1.0-nolibc/s390-linux/bin/s390-linux- /kisskb/src/arch/s390/kernel/syscall.c: In function '__do_syscall': /kisskb/src/arch/s390/kernel/syscall.c:168:1: warning: '__do_syscall' uses dynamic stack allocation } ^ /kisskb/src/kernel/trace/trace_osnoise.c: In function 'start_kthread': /kisskb/src/kernel/trace/trace_osnoise.c:1461:8: warning: 'main' is usually a function [-Wmain] void *main = osnoise_main; ^~~~ /kisskb/src/lib/test_scanf.c: In function 'numbers_list_field_width_val_width': /kisskb/src/lib/test_scanf.c:530:1: warning: the frame size of 2488 bytes is larger than 2048 bytes [-Wframe-larger-than=] } ^ /kisskb/src/lib/test_scanf.c: In function 'numbers_list_field_width_typemax': /kisskb/src/lib/test_scanf.c:488:1: warning: the frame size of 2976 bytes is larger than 2048 bytes [-Wframe-larger-than=] } ^ /kisskb/src/lib/test_scanf.c: In function 'numbers_list': /kisskb/src/lib/test_scanf.c:437:1: warning: the frame size of 2488 bytes is larger than 2048 bytes [-Wframe-larger-than=] } ^ /kisskb/src/drivers/input/joystick/analog.c:160:2: warning: #warning Precise timer not defined for this architecture. [-Wcpp] #warning Precise timer not defined for this architecture. ^~~~~~~ /kisskb/src/drivers/gpu/drm/rockchip/cdn-dp-core.c:1126:12: warning: 'cdn_dp_resume' defined but not used [-Wunused-function] static int cdn_dp_resume(struct device *dev) ^~~~~~~~~~~~~ In file included from /kisskb/src/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c:42: /kisskb/src/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c: In function 'mvpp2_setup_bm_pool': /kisskb/src/drivers/net/ethernet/marvell/mvpp2/mvpp2.h:844:2: warning: overflow in conversion from 'long unsigned int' to 'int' changes value from '18446744073709551584' to '-32' [-Woverflow] ((total_size) - MVPP2_SKB_HEADROOM - MVPP2_SKB_SHINFO_SIZE) ^ /kisskb/src/drivers/net/ethernet/marvell/mvpp2/mvpp2.h:948:33: note: in expansion of macro 'MVPP2_RX_MAX_PKT_SIZE' #define MVPP2_BM_SHORT_PKT_SIZE MVPP2_RX_MAX_PKT_SIZE(MVPP2_BM_SHORT_FRAME_SIZE) ^~~~~~~~~~~~~~~~~~~~~ /kisskb/src/drivers/net/ethernet/marvell/mvpp2/mvpp2_main.c:683:41: note: in expansion of macro 'MVPP2_BM_SHORT_PKT_SIZE' mvpp2_pools[MVPP2_BM_SHORT].pkt_size = MVPP2_BM_SHORT_PKT_SIZE; ^~~~~~~~~~~~~~~~~~~~~~~ Completed OK # rm -rf /kisskb/build/linus_s390-allmodconfig_s390x-gcc8 # Build took: 0:23:00.349639