bpf: Add function to extract program source info

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.

Reviewed-by: Emil Tsalapatis <[email protected]>
Signed-off-by: Kumar Kartikeya Dwivedi <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Alexei Starovoitov <[email protected]>

Author: kkdwivedi

include/linux/bpf.h

@@ -3661,4 +3661,7 @@ 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 */

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 || !jited_linfo)
+		return -EINVAL;
+	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)
+		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