Re: [PATCH bpf] bpf, bpftool: Fix incorrect disasm pc

[Leon Hwang <leon.hwang@linux.dev>]

On 2024/10/30 17:47, Leon Hwang wrote:
> From: Leon Hwang <leon.hwang@linux.dev>
> 
> 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@linux.dev>
> ---
>  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)

It seems we should update the type of pc from int to __u64, as the type
of func_ksym is __u64 and the type of pc argument in disassemble
function of LLVM and libbfd is __u64 for 64 bit arch.

Thanks,
Leon

>  	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);
>  
>  		if (json_output) {
>  			/* Operand array, was started in fprintf_json. Before