From: Nathan Chancellor <natechancellor@gmail.com>
To: Mark Rutland <mark.rutland@arm.com>
Cc: clang-built-linux@googlegroups.com,
Nick Desaulniers <ndesaulniers@google.com>,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org
Subject: Re: Enabling UBSAN breaks KCOV in clang (8.0.*) on arm64
Date: Tue, 20 Aug 2019 00:28:09 -0700 [thread overview]
Message-ID: <20190820072809.GA62296@archlinux-threadripper> (raw)
In-Reply-To: <20190819165947.GA30292@lakrids.cambridge.arm.com>
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
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prev parent reply other threads:[~2019-08-20 7:28 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-19 16:59 Enabling UBSAN breaks KCOV in clang (8.0.*) on arm64 Mark Rutland
2019-08-20 7:28 ` Nathan Chancellor [this message]
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