2024-10-30 17:47 UTC+0800 ~ Leon Hwang <hffilwlqm@xxxxxxxxx> > From: Leon Hwang <leon.hwang@xxxxxxxxx> > > This patch addresses the bpftool issue "Wrong callq address displayed"[0]. > > The issue stemmed from an incorrect program counter (PC) value used during > disassembly with LLVM or libbfd. To calculate the correct address for > relative calls, the PC argument must reflect the actual address in the > kernel. > > [0] https://github.com/libbpf/bpftool/issues/109 > > Fixes: e1947c750ffe ("bpftool: Refactor disassembler for JIT-ed programs") > Signed-off-by: Leon Hwang <leon.hwang@xxxxxxxxx> > --- > tools/bpf/bpftool/jit_disasm.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/tools/bpf/bpftool/jit_disasm.c b/tools/bpf/bpftool/jit_disasm.c > index 7b8d9ec89ebd3..fe8fabba4b05f 100644 > --- a/tools/bpf/bpftool/jit_disasm.c > +++ b/tools/bpf/bpftool/jit_disasm.c > @@ -114,8 +114,7 @@ disassemble_insn(disasm_ctx_t *ctx, unsigned char *image, ssize_t len, int pc) > char buf[256]; > int count; > > - count = LLVMDisasmInstruction(*ctx, image + pc, len - pc, pc, > - buf, sizeof(buf)); > + count = LLVMDisasmInstruction(*ctx, image, len, pc, buf, sizeof(buf)); > if (json_output) > printf_json(buf); > else > @@ -360,7 +359,8 @@ int disasm_print_insn(unsigned char *image, ssize_t len, int opcodes, > printf("%4x:" DISASM_SPACER, pc); > } > > - count = disassemble_insn(&ctx, image, len, pc); > + count = disassemble_insn(&ctx, image + pc, len - pc, > + func_ksym + pc); Thanks a lot for looking into this! Your patch does solve the issue for the LLVM disassembler (nice!), but it breaks the libbfd one: $ ./bpftool version | grep features features: libbfd # ./bpftool prog dump j id 111 op int xdp_redirect_map_0(struct xdp_md * xdp): bpf_prog_a8f6f9c4be77b94c_xdp_redirect_map_0: ; return bpf_redirect_map(&tx_port, 0, 0); 0: Address 0xffffffffc01ae950 is out of bounds. I don't think we can change the PC in the case of libbfd, as far as I can tell it needs to point to the first instruction to disassemble. Two of the arguments we pass to disassemble_insn(), image and len, are ignored by the libbfd disassembler; so it leaves only the ctx argument that we can maybe update to pass the func_ksym, but I haven't found how to do that yet (if possible at all). Thanks, Quentin pw-bot: cr
