[PATCH bpf-next v3 03/12] bpf: Add function to extract program source info

[Kumar Kartikeya Dwivedi <memxor@gmail.com>]

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@gmail.com>
---
 include/linux/bpf.h |  3 +++
 kernel/bpf/core.c   | 47 +++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 50 insertions(+)

diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index cdd726cfe622..f30697c72ba9 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -3667,4 +3667,7 @@ 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;
+	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
-- 
2.47.1