netdev - [PATCHv2 bpf-next 2/4] fprobe: Resolve symbols with kallsyms_lookup

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Date:   Mon, 18 Apr 2022 14:48:32 +0200
From:   Jiri Olsa <jolsa@...nel.org>
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org,
        lkml <linux-kernel@...r.kernel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>
Subject: [PATCHv2 bpf-next 2/4] fprobe: Resolve symbols with kallsyms_lookup_names

Using kallsyms_lookup_names to speed up symbols lookup
in register_fprobe_syms API.

This requires syms array to be alphabetically sorted.

Signed-off-by: Jiri Olsa <jolsa@...nel.org>
---
 kernel/trace/fprobe.c | 32 ++++++++++++--------------------
 1 file changed, 12 insertions(+), 20 deletions(-)

diff --git a/kernel/trace/fprobe.c b/kernel/trace/fprobe.c
index 89d9f994ebb0..6419501a0036 100644
--- a/kernel/trace/fprobe.c
+++ b/kernel/trace/fprobe.c
@@ -85,39 +85,31 @@ static void fprobe_exit_handler(struct rethook_node *rh, void *data,
 }
 NOKPROBE_SYMBOL(fprobe_exit_handler);
 
+static int symbols_cmp(const void *a, const void *b)
+{
+	const char **str_a = (const char **) a;
+	const char **str_b = (const char **) b;
+
+	return strcmp(*str_a, *str_b);
+}
+
 /* Convert ftrace location address from symbols */
 static unsigned long *get_ftrace_locations(const char **syms, int num)
 {
-	unsigned long addr, size;
 	unsigned long *addrs;
-	int i;
 
 	/* Convert symbols to symbol address */
 	addrs = kcalloc(num, sizeof(*addrs), GFP_KERNEL);
 	if (!addrs)
 		return ERR_PTR(-ENOMEM);
 
-	for (i = 0; i < num; i++) {
-		addr = kallsyms_lookup_name(syms[i]);
-		if (!addr)	/* Maybe wrong symbol */
-			goto error;
-
-		/* Convert symbol address to ftrace location. */
-		if (!kallsyms_lookup_size_offset(addr, &size, NULL) || !size)
-			goto error;
+	/* kallsyms_lookup_names expects sorted symbols */
+	sort(syms, num, sizeof(*syms), symbols_cmp, NULL);
 
-		addr = ftrace_location_range(addr, addr + size - 1);
-		if (!addr) /* No dynamic ftrace there. */
-			goto error;
+	if (!kallsyms_lookup_names(syms, num, addrs))
+		return addrs;
 
-		addrs[i] = addr;
-	}
-
-	return addrs;
-
-error:
 	kfree(addrs);
-
 	return ERR_PTR(-ENOENT);
 }
 
-- 
2.35.1