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selftests/bpf: Fix pyperf180 compilation failure with clang18
[ Upstream commit100888fb6d
] 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]1a2e77cf9e
Signed-off-by: Yonghong Song <yonghong.song@linux.dev> Signed-off-by: Andrii Nakryiko <andrii@kernel.org> Tested-by: Alan Maguire <alan.maguire@oracle.com> Link: https://lore.kernel.org/bpf/20231110193644.3130906-1-yonghong.song@linux.dev Signed-off-by: Sasha Levin <sashal@kernel.org>
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// SPDX-License-Identifier: GPL-2.0
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// Copyright (c) 2019 Facebook
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#define STACK_MAX_LEN 180
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/* llvm upstream commit at clang18
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* https://github.com/llvm/llvm-project/commit/1a2e77cf9e11dbf56b5720c607313a566eebb16e
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* changed inlining behavior and caused compilation failure as some branch
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* target distance exceeded 16bit representation which is the maximum for
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* cpu v1/v2/v3. Macro __BPF_CPU_VERSION__ is later implemented in clang18
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* to specify which cpu version is used for compilation. So a smaller
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* unroll_count can be set if __BPF_CPU_VERSION__ is less than 4, which
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* reduced some branch target distances and resolved the compilation failure.
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*
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* To capture the case where a developer/ci uses clang18 but the corresponding
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* repo checkpoint does not have __BPF_CPU_VERSION__, a smaller unroll_count
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* will be set as well to prevent potential compilation failures.
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*/
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#ifdef __BPF_CPU_VERSION__
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#if __BPF_CPU_VERSION__ < 4
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#define UNROLL_COUNT 90
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#endif
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#elif __clang_major__ == 18
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#define UNROLL_COUNT 90
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#endif
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#include "pyperf.h"
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