On Mon, Aug 19, 2019 at 05:59:48PM +0100, Mark Rutland wrote: > Hi, > > I found that when I enable both KCOV and UBSAN on arm64, clang fails to > emit any __sanitizer_cov_trace_*() calls in the resulting binary, > rendering KCOV useless. > > For example, when building v5.3-rc3's arch/arm64/kernel/setup.o: > > * With defconfig + CONFIG KCOV: > > clang -Wp,-MD,arch/arm64/kernel/.setup.o.d -nostdinc -isystem > > /mnt/data/opt/toolchain/llvm/8.0.0/clang+llvm-8.0.0-x86_64-linux-sles11.3/lib/clang/8.0.0/include > -I./arch/arm64/include -I./arch/arm64/include/generated -I./include > -I./arch/arm64/include/uapi -I./arch/arm64/include/generated/uapi > -I./include/uapi -I./include/generated/uapi -include > ./include/linux/kconfig.h -include ./include/linux/compiler_types.h > -D__KERNEL__ -mlittle-endian -DKASAN_SHADOW_SCALE_SHIFT=3 > -Qunused-arguments -Wall -Wundef -Werror=strict-prototypes > -Wno-trigraphs -fno-strict-aliasing -fno-common -fshort-wchar -fno-PIE > -Werror=implicit-function-declaration -Werror=implicit-int > -Wno-format-security -std=gnu89 --target=aarch64-linux > > --prefix=/mnt/data/opt/toolchain/kernel-org-crosstool/gcc-8.1.0-nolibc/aarch64-linux/bin/ > > --gcc-toolchain=/mnt/data/opt/toolchain/kernel-org-crosstool/gcc-8.1.0-nolibc/aarch64-linux > -no-integrated-as -Werror=unknown-warning-option -mgeneral-regs-only > -DCONFIG_AS_LSE=1 -fno-asynchronous-unwind-tables > -DKASAN_SHADOW_SCALE_SHIFT=3 -fno-delete-null-pointer-checks > -Wno-address-of-packed-member -O2 -Wframe-larger-than=2048 > -fstack-protector-strong -Wno-format-invalid-specifier -Wno-gnu > -Wno-tautological-compare -mno-global-merge -Wno-unused-const-variable > -fno-omit-frame-pointer -fno-optimize-sibling-calls -g > -Wdeclaration-after-statement -Wvla -Wno-pointer-sign > -fno-strict-overflow -fno-merge-all-constants -fno-stack-check > -Werror=date-time -Werror=incompatible-pointer-types > -Wno-initializer-overrides -Wno-format -Wno-sign-compare > -Wno-format-zero-length -fsanitize-coverage=trace-pc > -DKBUILD_BASENAME='"setup"' -DKBUILD_MODNAME='"setup"' -c -o > arch/arm64/kernel/setup.o arch/arm64/kernel/setup.c > > ... and there are 44 calls to __sanitizer_cov_trace_pc in the > resulting setup.o > > * with defconfig + CONFIG_KCOV + CONFIG_UBSAN: > > clang -Wp,-MD,arch/arm64/kernel/.setup.o.d -nostdinc -isystem > > /mnt/data/opt/toolchain/llvm/8.0.0/clang+llvm-8.0.0-x86_64-linux-sles11.3/lib/clang/8.0.0/include > -I./arch/arm64/include -I./arch/arm64/include/generated -I./include > -I./arch/arm64/include/uapi -I./arch/arm64/include/generated/uapi > -I./include/uapi -I./include/generated/uapi -include > ./include/linux/kconfig.h -include ./include/linux/compiler_types.h > -D__KERNEL__ -mlittle-endian -DKASAN_SHADOW_SCALE_SHIFT=3 > -Qunused-arguments -Wall -Wundef -Werror=strict-prototypes > -Wno-trigraphs -fno-strict-aliasing -fno-common -fshort-wchar -fno-PIE > -Werror=implicit-function-declaration -Werror=implicit-int > -Wno-format-security -std=gnu89 --target=aarch64-linux > > --prefix=/mnt/data/opt/toolchain/kernel-org-crosstool/gcc-8.1.0-nolibc/aarch64-linux/bin/ > > --gcc-toolchain=/mnt/data/opt/toolchain/kernel-org-crosstool/gcc-8.1.0-nolibc/aarch64-linux > -no-integrated-as -Werror=unknown-warning-option -mgeneral-regs-only > -DCONFIG_AS_LSE=1 -fno-asynchronous-unwind-tables > -DKASAN_SHADOW_SCALE_SHIFT=3 -fno-delete-null-pointer-checks > -Wno-address-of-packed-member -O2 -Wframe-larger-than=2048 > -fstack-protector-strong -Wno-format-invalid-specifier -Wno-gnu > -Wno-tautological-compare -mno-global-merge -Wno-unused-const-variable > -fno-omit-frame-pointer -fno-optimize-sibling-calls -g > -Wdeclaration-after-statement -Wvla -Wno-pointer-sign > -fno-strict-overflow -fno-merge-all-constants -fno-stack-check > -Werror=date-time -Werror=incompatible-pointer-types > -Wno-initializer-overrides -Wno-format -Wno-sign-compare > -Wno-format-zero-length -fsanitize=shift > -fsanitize=integer-divide-by-zero -fsanitize=unreachable > -fsanitize=signed-integer-overflow -fsanitize=bounds > -fsanitize=object-size -fsanitize=bool -fsanitize=enum > -fsanitize-coverage=trace-pc -DKBUILD_BASENAME='"setup"' > -DKBUILD_MODNAME='"setup"' -c -o arch/arm64/kernel/setup.o > arch/arm64/kernel/setup.c > > ... and there are 0 calls to __sanitizer_cov_trace_pc in the resulting > setup.o, even though -fsanitize-coverage=trace-pc was passed to clang. > > If I remove -fsanitize=bounds, there are 121 calls to > __sanitizer_cov_trace_pc in setup.o. Removing the other options enabled > by UBSAN didn't have any effect on setup.o. > > I'm using the llvm.org 8.0.{0,1} binaries [1,2], along with the > kernel.org crosstool 8.1.0 binaries [3]. > > Any ideas as to what's going on? > > Thanks, > Mark. > > [1] http://releases.llvm.org/download.html#8.0.0 > [2] http://releases.llvm.org/download.html#8.0.1 > [3] https://mirrors.edge.kernel.org/pub/tools/crosstool/
Hi Mark, I've narrowed it down further; it seems that the combination of -fsanitize-coverage=trace-pc and -fsanitize=local-bounds prevents the emission of __sanitizer_cov_trace_pc. -fsanitize=bounds is the same as -fsanitize=local-bounds and -fsanitize=array-bounds, the latter of which has no issues. https://godbolt.org/z/YdF-he This reproducer was taken from a somewhat related bug report in April. https://bugs.llvm.org/show_bug.cgi?id=41387 What's also interesting is when you remove -Qunused-arguments from the clang command, the following warning appears (also visible in the godbolt link): clang-10: warning: argument unused during compilation: '-fsanitize-coverage=trace-pc' [-Wunused-command-line-argument] I have no idea why this combination is special, I've been searching the source trying to see what I can find and I am currently not coming up with anything (I'm sure a good night's rest will give me a fresh set of eyes). This is still an issue on Clang trunk. Cheers, Nathan