On Tue, Sep 6, 2022 at 6:36 AM Quentin Monnet <quentin@xxxxxxxxxxxxx> wrote: > > Naturally, the display of disassembled instructions comes with a few > minor differences. Here is a sample output with libbfd (already > supported before this patch): > > # bpftool prog dump jited id 56 > bpf_prog_6deef7357e7b4530: > 0: nopl 0x0(%rax,%rax,1) > 5: xchg %ax,%ax > 7: push %rbp > 8: mov %rsp,%rbp > b: push %rbx > c: push %r13 > e: push %r14 > 10: mov %rdi,%rbx > 13: movzwq 0xb0(%rbx),%r13 > 1b: xor %r14d,%r14d > 1e: or $0x2,%r14d > 22: mov $0x1,%eax > 27: cmp $0x2,%r14 > 2b: jne 0x000000000000002f > 2d: xor %eax,%eax > 2f: pop %r14 > 31: pop %r13 > 33: pop %rbx > 34: leave > 35: ret > 36: int3 > > LLVM supports several variants that we could set when initialising the > disassembler, for example with: > > LLVMSetDisasmOptions(*ctx, > LLVMDisassembler_Option_AsmPrinterVariant); > > but the default printer is kept for now. Here is the output with LLVM: > > # bpftool prog dump jited id 56 > bpf_prog_6deef7357e7b4530: > 0: nopl (%rax,%rax) > 5: nop > 7: pushq %rbp > 8: movq %rsp, %rbp > b: pushq %rbx > c: pushq %r13 > e: pushq %r14 > 10: movq %rdi, %rbx > 13: movzwq 176(%rbx), %r13 > 1b: xorl %r14d, %r14d > 1e: orl $2, %r14d > 22: movl $1, %eax > 27: cmpq $2, %r14 > 2b: jne 2 > 2d: xorl %eax, %eax > 2f: popq %r14 If I'm reading the asm correctly the difference is significant. jne 0x2f was an absolute address and jmps were easy to follow. While in llvm disasm it's 'jne 2' ?! What is 2 ? 2 bytes from the next insn of 0x2d ? That is super hard to read. Is there a way to tune/configure llvm disasm?
