linux-kernel - [PATCH 2/6] kallsyms: Cleanup code for appending the module buildid

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Message-ID: <20251105142319.1139183-3-pmladek@suse.com>
Date: Wed,  5 Nov 2025 15:23:14 +0100
From: Petr Mladek <pmladek@...e.com>
To: Petr Pavlu <petr.pavlu@...e.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Alexei Starovoitov <ast@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kees Cook <kees@...nel.org>
Cc: Daniel Borkmann <daniel@...earbox.net>,
	John Fastabend <john.fastabend@...il.com>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Luis Chamberlain <mcgrof@...nel.org>,
	Daniel Gomez <da.gomez@...nel.org>,
	Sami Tolvanen <samitolvanen@...gle.com>,
	linux-kernel@...r.kernel.org,
	bpf@...r.kernel.org,
	linux-modules@...r.kernel.org,
	linux-trace-kernel@...r.kernel.org,
	Petr Mladek <pmladek@...e.com>
Subject: [PATCH 2/6] kallsyms: Cleanup code for appending the module buildid

Put the code for appending the optional "buildid" into a helper
function, It makes __sprint_symbol() better readable.

Also print a warning when the "modname" is set and the "buildid" isn't.
It might catch a situation when some lookup function in
kallsyms_lookup_buildid() does not handle the "buildid".

Use pr_*_once() to avoid an infinite recursion when the function
is called from printk(). The recursion is rather theoretical but
better be on the safe side.

Signed-off-by: Petr Mladek <pmladek@...e.com>
---
 kernel/kallsyms.c | 42 +++++++++++++++++++++++++++++++++---------
 1 file changed, 33 insertions(+), 9 deletions(-)

diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index 1e7635864124..9455e3bb07fc 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -423,6 +423,37 @@ int lookup_symbol_name(unsigned long addr, char *symname)
 	return lookup_module_symbol_name(addr, symname);
 }
 
+#ifdef CONFIG_STACKTRACE_BUILD_ID
+
+static int append_buildid(char *buffer,  const char *modname,
+			  const unsigned char *buildid)
+{
+	if (!modname)
+		return 0;
+
+	if (!buildid) {
+		pr_warn_once("Undefined buildid for the module %s\n", modname);
+		return 0;
+	}
+
+	/* build ID should match length of sprintf */
+#ifdef CONFIG_MODULES
+	static_assert(sizeof(typeof_member(struct module, build_id)) == 20);
+#endif
+
+	return sprintf(buffer, " %20phN", buildid);
+}
+
+#else /* CONFIG_STACKTRACE_BUILD_ID */
+
+static int append_buildid(char *buffer,   const char *modname,
+			  const unsigned char *buildid)
+{
+	return 0;
+}
+
+#endif /* CONFIG_STACKTRACE_BUILD_ID */
+
 /* Look up a kernel symbol and return it in a text buffer. */
 static int __sprint_symbol(char *buffer, unsigned long address,
 			   int symbol_offset, int add_offset, int add_buildid)
@@ -445,15 +476,8 @@ static int __sprint_symbol(char *buffer, unsigned long address,
 
 	if (modname) {
 		len += sprintf(buffer + len, " [%s", modname);
-#if IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID)
-		if (add_buildid && buildid) {
-			/* build ID should match length of sprintf */
-#if IS_ENABLED(CONFIG_MODULES)
-			static_assert(sizeof(typeof_member(struct module, build_id)) == 20);
-#endif
-			len += sprintf(buffer + len, " %20phN", buildid);
-		}
-#endif
+		if (add_buildid)
+			len += append_buildid(buffer + len, modname, buildid);
 		len += sprintf(buffer + len, "]");
 	}
 
-- 
2.51.1