f122668d - ARC: Add eBPF JIT support

Tue, 30 Apr 2024 14:56:04 +0000

ARC: Add eBPF JIT supportThis will add eBPF JIT support to the 32-bit ARCv2 processors. Theimplementation is qualified by running the BPF tests on a Synopsys HSDKboard with "ARC HS38 v2.1c at 500 MHz" as the 4-core CPU.The test_bpf.ko reports 2-10 fold improvements in execution time of itstests. For instance:test_bpf: #33 tcpdump port 22 jited:0 704 1766 2104 PASStest_bpf: #33 tcpdump port 22 jited:1 120 224 260 PASStest_bpf: #141 ALU_DIV_X: 4294967295 / 4294967295 = 1 jited:0 238 PASStest_bpf: #141 ALU_DIV_X: 4294967295 / 4294967295 = 1 jited:1 23 PASStest_bpf: #776 JMP32_JGE_K: all ... magnitudes jited:0 2034681 PASStest_bpf: #776 JMP32_JGE_K: all ... magnitudes jited:1 1020022 PASSDeployment and structure------------------------The related codes are added to "arch/arc/net":- bpf_jit.h -- The interface that a back-end translator must provide- bpf_jit_core.c -- Knows how to handle the input eBPF byte stream- bpf_jit_arcv2.c -- The back-end code that knows the translation logicThe bpf_int_jit_compile() at the end of bpf_jit_core.c is the entranceto the whole process. Normally, the translation is done in one pass,namely the "normal pass". In case some relocations are not known duringthis pass, some data (arc_jit_data) is allocated for the next pass tocome. This possible next (and last) pass is called the "extra pass".1. Normal pass # The necessary pass 1a. Dry run # Get the whole JIT length, epilogue offset, etc. 1b. Emit phase # Allocate memory and start emitting instructions2. Extra pass # Only needed if there are relocations to be fixed 2a. Patch relocationsSupport status--------------The JIT compiler supports BPF instructions up to "cpu=v4". However, itdoes not yet provide support for:- Tail calls- Atomic operations- 64-bit division/remainder- BPF_PROBE_MEM* (exception table)The result of "test_bpf" test suite on an HSDK board is:hsdk-lnx# insmod test_bpf.ko test_suite=test_bpf test_bpf: Summary: 863 PASSED, 186 FAILED, [851/851 JIT'ed]All the failing test cases are due to the ones that were not JIT'ed.Categorically, they can be represented as: .-----------.------------.-------------. | test type | opcodes | # of cases | |-----------+------------+-------------| | atomic | 0xC3, 0xDB | 149 | | div64 | 0x37, 0x3F | 22 | | mod64 | 0x97, 0x9F | 15 | `-----------^------------+-------------| | (total) 186 | `-------------'Setup: build config-------------------The following configs must be set to have a working JIT test: CONFIG_BPF_JIT=y CONFIG_BPF_JIT_ALWAYS_ON=y CONFIG_TEST_BPF=mThe following options are not necessary for the tests module,but are good to have: CONFIG_DEBUG_INFO=y # prerequisite for below CONFIG_DEBUG_INFO_BTF=y # so bpftool can generate vmlinux.h CONFIG_FTRACE=y # CONFIG_BPF_SYSCALL=y # all these options lead to CONFIG_KPROBE_EVENTS=y # having CONFIG_BPF_EVENTS=y CONFIG_PERF_EVENTS=y #Some BPF programs provide data through /sys/kernel/debug: CONFIG_DEBUG_FS=yarc# mount -t debugfs debugfs /sys/kernel/debugSetup: elfutils---------------The libdw.{so,a} library that is used by pahole for processingthe final binary must come from elfutils 0.189 or newer. Thesupport for ARCv2 [1] has been added since that version.[1]https://sourceware.org/git/?p=elfutils.git;a=commit;h=de3d46b3e7Setup: pahole-------------The line below in linux/scripts/Makefile.btf must be commented out:pahole-flags-$(call test-ge, $(pahole-ver), 121) += --btf_gen_floatsOr else, the build will fail:$ make V=1 ... BTF .btf.vmlinux.bin.opahole -J --btf_gen_floats \ -j --lang_exclude=rust \ --skip_encoding_btf_inconsistent_proto \ --btf_gen_optimized .tmp_vmlinux.btfComplex, interval and imaginary float types are not supportedEncountered error while encoding BTF. ... BTFIDS vmlinux./tools/bpf/resolve_btfids/resolve_btfids vmlinuxlibbpf: failed to find '.BTF' ELF section in vmlinuxFAILED: load BTF from vmlinux: No data availableThis is due to the fact that the ARC toolchains generate"complex float" DIE entries in libgcc and at the moment, paholecan't handle such entries.Running the tests-----------------host$ scp /bld/linux/lib/test_bpf.ko arc:arc # sysctl net.core.bpf_jit_enable=1arc # insmod test_bpf.ko test_suite=test_bpf ... test_bpf: #1048 Staggered jumps: JMP32_JSLE_X jited:1 697811 PASS test_bpf: Summary: 863 PASSED, 186 FAILED, [851/851 JIT'ed]Acknowledgments---------------- Claudiu Zissulescu for his unwavering support- Yuriy Kolerov for testing and troubleshooting- Vladimir Isaev for the pahole workaround- Sergey Matyukevich for paving the road by adding the interpreter supportSigned-off-by: Shahab Vahedi Link: https://lore.kernel.org/r/20240430145604.38592-1-list+bpf@vahedi.orgSigned-off-by: Alexei Starovoitov List of files: /linux-6.15/arch/arc/net/Makefile

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f122668d - ARC: Add eBPF JIT support