selftests/bpf: utility function to get program disassembly after jit

2024-08-21T18:03:01Z

This commit adds a utility function to get disassembled text for jited representation of a BPF program designated by file descriptor. Function prototype looks as follows: int get_jited_program_text(int fd, char *text, size_t text_sz) Where 'fd' is a file descriptor for the program, 'text' and 'text_sz' refer to a destination buffer for disassembled text. Output format looks as follows: 18: 77 06 ja L0 1a: 50 pushq %rax 1b: 48 89 e0 movq %rsp, %rax 1e: eb 01 jmp L1 20: 50 L0: pushq %rax 21: 50 L1: pushq %rax ^ ^^^^^^^^ ^ ^^^^^^^^^^^^^^^^^^ | binary insn | textual insn | representation | representation | | instruction offset inferred local label name The code and makefile changes are inspired by jit_disasm.c from bpftool. Use llvm libraries to disassemble BPF program instead of libbfd to avoid issues with disassembly output stability pointed out in [1]. Selftests makefile uses Makefile.feature to detect if LLVM libraries are available. If that is not the case selftests build proceeds but the function returns -EOPNOTSUPP at runtime. [1] commit eb9d1acf634b ("bpftool: Add LLVM as default library for disassembling JIT-ed programs") Acked-by: Yonghong Song Signed-off-by: Eduard Zingerman Link: https://lore.kernel.org/r/20240820102357.3372779-6-eddyz87@gmail.com Signed-off-by: Alexei Starovoitov

kernel/tools/testing/selftests/bpf/jit_disasm_helpers.h, branch linux-rolling-stable

selftests/bpf: utility function to get program disassembly after jit