On Tue, Jul 1, 2025 at 11:17 PM Kumar Kartikeya Dwivedi
<memxor@xxxxxxxxx> wrote:
>
> Prepare a function for use in future patches that can extract the file
> info, line info, and the source line number for a given BPF program
> provided it's program counter.
>
> Only the basename of the file path is provided, given it can be
> excessively long in some cases.
>
> This will be used in later patches to print source info to the BPF
> stream.
>
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>
> ---
> include/linux/bpf.h | 3 +++
> kernel/bpf/core.c | 47 +++++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 50 insertions(+)
>
Nits aside:
Reviewed-by: Emil Tsalapatis <emil@xxxxxxxxxxxxxxx>
> diff --git a/include/linux/bpf.h b/include/linux/bpf.h
> index 85b1cbe494f5..09f06b1ea62e 100644
> --- a/include/linux/bpf.h
> +++ b/include/linux/bpf.h
> @@ -3660,4 +3660,7 @@ static inline bool bpf_is_subprog(const struct bpf_prog *prog)
> return prog->aux->func_idx != 0;
> }
>
> +int bpf_prog_get_file_line(struct bpf_prog *prog, unsigned long ip, const char **filep,
> + const char **linep, int *nump);
> +
> #endif /* _LINUX_BPF_H */
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index f0def24573ae..5c6e9fbb5508 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -3213,3 +3213,50 @@ EXPORT_SYMBOL(bpf_stats_enabled_key);
>
> EXPORT_TRACEPOINT_SYMBOL_GPL(xdp_exception);
> EXPORT_TRACEPOINT_SYMBOL_GPL(xdp_bulk_tx);
> +
> +#ifdef CONFIG_BPF_SYSCALL
> +
> +int bpf_prog_get_file_line(struct bpf_prog *prog, unsigned long ip, const char **filep,
> + const char **linep, int *nump)
> +{
> + int idx = -1, insn_start, insn_end, len;
> + struct bpf_line_info *linfo;
> + void **jited_linfo;
> + struct btf *btf;
> +
> + btf = prog->aux->btf;
> + linfo = prog->aux->linfo;
> + jited_linfo = prog->aux->jited_linfo;
> +
> + if (!btf || !linfo || !prog->aux->jited_linfo)
> + return -EINVAL;
Either use jited_linfo in the condition, or remove the shorthands
above sin ce btf and
jited_linfo immediately get overwritten anyway.
> + len = prog->aux->func ? prog->aux->func[prog->aux->func_idx]->len : prog->len;
> +
> + linfo = &prog->aux->linfo[prog->aux->linfo_idx];
> + jited_linfo = &prog->aux->jited_linfo[prog->aux->linfo_idx];
> +
> + insn_start = linfo[0].insn_off;
> + insn_end = insn_start + len;
> +
> + for (int i = 0; i < prog->aux->nr_linfo &&
> + linfo[i].insn_off >= insn_start && linfo[i].insn_off < insn_end; i++) {
> + if (jited_linfo[i] >= (void *)ip)
> + break;
> + idx = i;
> + }
> +
> + if (idx == -1)
This doesn't catch the case where we exhaust the loop without ever
triggering the
jited_linfo[i] >= (void *)ip branch. Is it worth using (jited_linfo[i]
< (void *)ip as the
error condition instead, or do we not need to account for it?
> + return -ENOENT;
> +
> + /* Get base component of the file path. */
> + *filep = btf_name_by_offset(btf, linfo[idx].file_name_off);
> + *filep = kbasename(*filep);
> + /* Obtain the source line, and strip whitespace in prefix. */
> + *linep = btf_name_by_offset(btf, linfo[idx].line_off);
> + while (isspace(**linep))
> + *linep += 1;
> + *nump = BPF_LINE_INFO_LINE_NUM(linfo[idx].line_col);
> + return 0;
> +}
> +
> +#endif
> --
> 2.47.1
>
