| Message ID | 20231110193644.3130906-1-yonghong.song@linux.dev (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 100888fb6d8a185866b1520031ee7e3182b173de |
| Delegated to: | BPF |
| Headers | show |
| Series | [bpf-next,v2] selftests/bpf: Fix pyperf180 compilation failure with clang18 | expand |
On Fri, Nov 10, 2023 at 11:37 AM Yonghong Song <yonghong.song@linux.dev> wrote: > > With latest clang18 (main branch of llvm-project repo), when building bpf selftests, > [~/work/bpf-next (master)]$ make -C tools/testing/selftests/bpf LLVM=1 -j > > The following compilation error happens: > fatal error: error in backend: Branch target out of insn range > ... > Stack dump: > 0. Program arguments: clang -g -Wall -Werror -D__TARGET_ARCH_x86 -mlittle-endian > -I/home/yhs/work/bpf-next/tools/testing/selftests/bpf/tools/include > -I/home/yhs/work/bpf-next/tools/testing/selftests/bpf -I/home/yhs/work/bpf-next/tools/include/uapi > -I/home/yhs/work/bpf-next/tools/testing/selftests/usr/include -idirafter > /home/yhs/work/llvm-project/llvm/build.18/install/lib/clang/18/include -idirafter /usr/local/include > -idirafter /usr/include -Wno-compare-distinct-pointer-types -DENABLE_ATOMICS_TESTS -O2 --target=bpf > -c progs/pyperf180.c -mcpu=v3 -o /home/yhs/work/bpf-next/tools/testing/selftests/bpf/pyperf180.bpf.o > 1. <eof> parser at end of file > 2. Code generation > ... > > The compilation failure only happens to cpu=v2 and cpu=v3. cpu=v4 is okay > since cpu=v4 supports 32-bit branch target offset. > > The above failure is due to upstream llvm patch [1] where some inlining behavior > are changed in clang18. > > To workaround the issue, previously all 180 loop iterations are fully unrolled. > The bpf macro __BPF_CPU_VERSION__ (implemented in clang18 recently) is used to avoid > unrolling changes if cpu=v4. If __BPF_CPU_VERSION__ is not available and the > compiler is clang18, the unrollng amount is unconditionally reduced. > > [1] https://github.com/llvm/llvm-project/commit/1a2e77cf9e11dbf56b5720c607313a566eebb16e > > Signed-off-by: Yonghong Song <yonghong.song@linux.dev> > --- > tools/testing/selftests/bpf/progs/pyperf180.c | 22 +++++++++++++++++++ > 1 file changed, 22 insertions(+) > > diff --git a/tools/testing/selftests/bpf/progs/pyperf180.c b/tools/testing/selftests/bpf/progs/pyperf180.c > index c39f559d3100..42c4a8b62e36 100644 > --- a/tools/testing/selftests/bpf/progs/pyperf180.c > +++ b/tools/testing/selftests/bpf/progs/pyperf180.c > @@ -1,4 +1,26 @@ > // SPDX-License-Identifier: GPL-2.0 > // Copyright (c) 2019 Facebook > #define STACK_MAX_LEN 180 > + > +/* llvm upstream commit at clang18 > + * https://github.com/llvm/llvm-project/commit/1a2e77cf9e11dbf56b5720c607313a566eebb16e > + * changed inlining behavior and caused compilation failure as some branch > + * target distance exceeded 16bit representation which is the maximum for > + * cpu v1/v2/v3. Macro __BPF_CPU_VERSION__ is later implemented in clang18 > + * to specify which cpu version is used for compilation. So a smaller > + * unroll_count can be set if __BPF_CPU_VERSION__ is less than 4, which > + * reduced some branch target distances and resolved the compilation failure. > + * > + * To capture the case where a developer/ci uses clang18 but the corresponding > + * repo checkpoint does not have __BPF_CPU_VERSION__, a smaller unroll_count > + * will be set as well to prevent potential compilation failures. > + */ > +#ifdef __BPF_CPU_VERSION__ > +#if __BPF_CPU_VERSION__ < 4 > +#define UNROLL_COUNT 90 > +#endif > +#elif __clang_major__ == 18 > +#define UNROLL_COUNT 90 > +#endif > + can it be written as one if? #if (defined(__BPF_CPU_VERSION__) && __BPF_CPU_VERSION__ < 4) || __clang_major >= 18 ? > #include "pyperf.h" > -- > 2.34.1 > >
On 10/11/2023 19:36, Yonghong Song wrote: > With latest clang18 (main branch of llvm-project repo), when building bpf selftests, > [~/work/bpf-next (master)]$ make -C tools/testing/selftests/bpf LLVM=1 -j > > The following compilation error happens: > fatal error: error in backend: Branch target out of insn range > ... > Stack dump: > 0. Program arguments: clang -g -Wall -Werror -D__TARGET_ARCH_x86 -mlittle-endian > -I/home/yhs/work/bpf-next/tools/testing/selftests/bpf/tools/include > -I/home/yhs/work/bpf-next/tools/testing/selftests/bpf -I/home/yhs/work/bpf-next/tools/include/uapi > -I/home/yhs/work/bpf-next/tools/testing/selftests/usr/include -idirafter > /home/yhs/work/llvm-project/llvm/build.18/install/lib/clang/18/include -idirafter /usr/local/include > -idirafter /usr/include -Wno-compare-distinct-pointer-types -DENABLE_ATOMICS_TESTS -O2 --target=bpf > -c progs/pyperf180.c -mcpu=v3 -o /home/yhs/work/bpf-next/tools/testing/selftests/bpf/pyperf180.bpf.o > 1. <eof> parser at end of file > 2. Code generation > ... > > The compilation failure only happens to cpu=v2 and cpu=v3. cpu=v4 is okay > since cpu=v4 supports 32-bit branch target offset. > > The above failure is due to upstream llvm patch [1] where some inlining behavior > are changed in clang18. > > To workaround the issue, previously all 180 loop iterations are fully unrolled. > The bpf macro __BPF_CPU_VERSION__ (implemented in clang18 recently) is used to avoid > unrolling changes if cpu=v4. If __BPF_CPU_VERSION__ is not available and the > compiler is clang18, the unrollng amount is unconditionally reduced. > > [1] https://github.com/llvm/llvm-project/commit/1a2e77cf9e11dbf56b5720c607313a566eebb16e > > Signed-off-by: Yonghong Song <yonghong.song@linux.dev> Fixes the issue for me; Tested-by: Alan Maguire <alan.maguire@oracle.com>
On 11/10/23 11:45 AM, Andrii Nakryiko wrote: > On Fri, Nov 10, 2023 at 11:37 AM Yonghong Song <yonghong.song@linux.dev> wrote: >> With latest clang18 (main branch of llvm-project repo), when building bpf selftests, >> [~/work/bpf-next (master)]$ make -C tools/testing/selftests/bpf LLVM=1 -j >> >> The following compilation error happens: >> fatal error: error in backend: Branch target out of insn range >> ... >> Stack dump: >> 0. Program arguments: clang -g -Wall -Werror -D__TARGET_ARCH_x86 -mlittle-endian >> -I/home/yhs/work/bpf-next/tools/testing/selftests/bpf/tools/include >> -I/home/yhs/work/bpf-next/tools/testing/selftests/bpf -I/home/yhs/work/bpf-next/tools/include/uapi >> -I/home/yhs/work/bpf-next/tools/testing/selftests/usr/include -idirafter >> /home/yhs/work/llvm-project/llvm/build.18/install/lib/clang/18/include -idirafter /usr/local/include >> -idirafter /usr/include -Wno-compare-distinct-pointer-types -DENABLE_ATOMICS_TESTS -O2 --target=bpf >> -c progs/pyperf180.c -mcpu=v3 -o /home/yhs/work/bpf-next/tools/testing/selftests/bpf/pyperf180.bpf.o >> 1. <eof> parser at end of file >> 2. Code generation >> ... >> >> The compilation failure only happens to cpu=v2 and cpu=v3. cpu=v4 is okay >> since cpu=v4 supports 32-bit branch target offset. >> >> The above failure is due to upstream llvm patch [1] where some inlining behavior >> are changed in clang18. >> >> To workaround the issue, previously all 180 loop iterations are fully unrolled. >> The bpf macro __BPF_CPU_VERSION__ (implemented in clang18 recently) is used to avoid >> unrolling changes if cpu=v4. If __BPF_CPU_VERSION__ is not available and the >> compiler is clang18, the unrollng amount is unconditionally reduced. >> >> [1] https://github.com/llvm/llvm-project/commit/1a2e77cf9e11dbf56b5720c607313a566eebb16e >> >> Signed-off-by: Yonghong Song <yonghong.song@linux.dev> >> --- >> tools/testing/selftests/bpf/progs/pyperf180.c | 22 +++++++++++++++++++ >> 1 file changed, 22 insertions(+) >> >> diff --git a/tools/testing/selftests/bpf/progs/pyperf180.c b/tools/testing/selftests/bpf/progs/pyperf180.c >> index c39f559d3100..42c4a8b62e36 100644 >> --- a/tools/testing/selftests/bpf/progs/pyperf180.c >> +++ b/tools/testing/selftests/bpf/progs/pyperf180.c >> @@ -1,4 +1,26 @@ >> // SPDX-License-Identifier: GPL-2.0 >> // Copyright (c) 2019 Facebook >> #define STACK_MAX_LEN 180 >> + >> +/* llvm upstream commit at clang18 >> + * https://github.com/llvm/llvm-project/commit/1a2e77cf9e11dbf56b5720c607313a566eebb16e >> + * changed inlining behavior and caused compilation failure as some branch >> + * target distance exceeded 16bit representation which is the maximum for >> + * cpu v1/v2/v3. Macro __BPF_CPU_VERSION__ is later implemented in clang18 >> + * to specify which cpu version is used for compilation. So a smaller >> + * unroll_count can be set if __BPF_CPU_VERSION__ is less than 4, which >> + * reduced some branch target distances and resolved the compilation failure. >> + * >> + * To capture the case where a developer/ci uses clang18 but the corresponding >> + * repo checkpoint does not have __BPF_CPU_VERSION__, a smaller unroll_count >> + * will be set as well to prevent potential compilation failures. >> + */ >> +#ifdef __BPF_CPU_VERSION__ >> +#if __BPF_CPU_VERSION__ < 4 >> +#define UNROLL_COUNT 90 >> +#endif >> +#elif __clang_major__ == 18 >> +#define UNROLL_COUNT 90 >> +#endif >> + > can it be written as one if? > > #if (defined(__BPF_CPU_VERSION__) && __BPF_CPU_VERSION__ < 4) || > __clang_major >= 18 > > > ? This won't work. For example, using latest upstream clang18, __BPF_CPU_VERSION__ does exist, and user use cpu v4, in this case we do not want to do unrolling but with the above: (defined(__BPF_CPU_VERSION__) && __BPF_CPU_VERSION__ < 4) is false __clang_major >= 18 is true so we do unrolling but we do not need to do since user uses cpu v4. > >> #include "pyperf.h" >> -- >> 2.34.1 >> >>
Hello: This patch was applied to bpf/bpf-next.git (master) by Andrii Nakryiko <andrii@kernel.org>: On Fri, 10 Nov 2023 11:36:44 -0800 you wrote: > With latest clang18 (main branch of llvm-project repo), when building bpf selftests, > [~/work/bpf-next (master)]$ make -C tools/testing/selftests/bpf LLVM=1 -j > > The following compilation error happens: > fatal error: error in backend: Branch target out of insn range > ... > Stack dump: > 0. Program arguments: clang -g -Wall -Werror -D__TARGET_ARCH_x86 -mlittle-endian > -I/home/yhs/work/bpf-next/tools/testing/selftests/bpf/tools/include > -I/home/yhs/work/bpf-next/tools/testing/selftests/bpf -I/home/yhs/work/bpf-next/tools/include/uapi > -I/home/yhs/work/bpf-next/tools/testing/selftests/usr/include -idirafter > /home/yhs/work/llvm-project/llvm/build.18/install/lib/clang/18/include -idirafter /usr/local/include > -idirafter /usr/include -Wno-compare-distinct-pointer-types -DENABLE_ATOMICS_TESTS -O2 --target=bpf > -c progs/pyperf180.c -mcpu=v3 -o /home/yhs/work/bpf-next/tools/testing/selftests/bpf/pyperf180.bpf.o > 1. <eof> parser at end of file > 2. Code generation > ... > > [...] Here is the summary with links: - [bpf-next,v2] selftests/bpf: Fix pyperf180 compilation failure with clang18 https://git.kernel.org/bpf/bpf-next/c/100888fb6d8a You are awesome, thank you!
diff --git a/tools/testing/selftests/bpf/progs/pyperf180.c b/tools/testing/selftests/bpf/progs/pyperf180.c index c39f559d3100..42c4a8b62e36 100644 --- a/tools/testing/selftests/bpf/progs/pyperf180.c +++ b/tools/testing/selftests/bpf/progs/pyperf180.c @@ -1,4 +1,26 @@ // SPDX-License-Identifier: GPL-2.0 // Copyright (c) 2019 Facebook #define STACK_MAX_LEN 180 + +/* llvm upstream commit at clang18 + * https://github.com/llvm/llvm-project/commit/1a2e77cf9e11dbf56b5720c607313a566eebb16e + * changed inlining behavior and caused compilation failure as some branch + * target distance exceeded 16bit representation which is the maximum for + * cpu v1/v2/v3. Macro __BPF_CPU_VERSION__ is later implemented in clang18 + * to specify which cpu version is used for compilation. So a smaller + * unroll_count can be set if __BPF_CPU_VERSION__ is less than 4, which + * reduced some branch target distances and resolved the compilation failure. + * + * To capture the case where a developer/ci uses clang18 but the corresponding + * repo checkpoint does not have __BPF_CPU_VERSION__, a smaller unroll_count + * will be set as well to prevent potential compilation failures. + */ +#ifdef __BPF_CPU_VERSION__ +#if __BPF_CPU_VERSION__ < 4 +#define UNROLL_COUNT 90 +#endif +#elif __clang_major__ == 18 +#define UNROLL_COUNT 90 +#endif + #include "pyperf.h"
With latest clang18 (main branch of llvm-project repo), when building bpf selftests, [~/work/bpf-next (master)]$ make -C tools/testing/selftests/bpf LLVM=1 -j The following compilation error happens: fatal error: error in backend: Branch target out of insn range ... Stack dump: 0. Program arguments: clang -g -Wall -Werror -D__TARGET_ARCH_x86 -mlittle-endian -I/home/yhs/work/bpf-next/tools/testing/selftests/bpf/tools/include -I/home/yhs/work/bpf-next/tools/testing/selftests/bpf -I/home/yhs/work/bpf-next/tools/include/uapi -I/home/yhs/work/bpf-next/tools/testing/selftests/usr/include -idirafter /home/yhs/work/llvm-project/llvm/build.18/install/lib/clang/18/include -idirafter /usr/local/include -idirafter /usr/include -Wno-compare-distinct-pointer-types -DENABLE_ATOMICS_TESTS -O2 --target=bpf -c progs/pyperf180.c -mcpu=v3 -o /home/yhs/work/bpf-next/tools/testing/selftests/bpf/pyperf180.bpf.o 1. <eof> parser at end of file 2. Code generation ... The compilation failure only happens to cpu=v2 and cpu=v3. cpu=v4 is okay since cpu=v4 supports 32-bit branch target offset. The above failure is due to upstream llvm patch [1] where some inlining behavior are changed in clang18. To workaround the issue, previously all 180 loop iterations are fully unrolled. The bpf macro __BPF_CPU_VERSION__ (implemented in clang18 recently) is used to avoid unrolling changes if cpu=v4. If __BPF_CPU_VERSION__ is not available and the compiler is clang18, the unrollng amount is unconditionally reduced. [1] https://github.com/llvm/llvm-project/commit/1a2e77cf9e11dbf56b5720c607313a566eebb16e Signed-off-by: Yonghong Song <yonghong.song@linux.dev> --- tools/testing/selftests/bpf/progs/pyperf180.c | 22 +++++++++++++++++++ 1 file changed, 22 insertions(+)