Michael Ellerman wrote:

"Naveen N. Rao" [off-list ref] writes:

quoted

diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index 6a3b249a2ae1..d134b060564f 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c

@@ -205,6 +205,12 @@ unsigned long kallsyms_lookup_name(const char *name)
 	unsigned long i;
 	unsigned int off;
 
+	if (!name || *name == '\0')
+		return false;
+
+	if (strnchr(name, MODULE_NAME_LEN, ':'))
+		return module_kallsyms_lookup_name(name);
+
 	for (i = 0, off = 0; i < kallsyms_num_syms; i++) {
 		off = kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf));

	...				
	}
       	return module_kallsyms_lookup_name(name);

Is the rest of the context.

Which looks a bit odd, we already did module lookup previously?

But it's correct, because you can lookup a symbol in a module without a
module prefix, it just looks in every module.

Yes.

You could invert the logic, ie. check that there isn't a ":" in the name
and only in that case do the for loop, always falling back to module
lookup.

Or just add a comment explaining why we call module lookup in two places.

Good point. Here's a v2 - I'm using a goto so as to not indent the code too much.

Thanks for the review!
- Naveen

--
[PATCH v2] kallsyms: optimize kallsyms_lookup_name() for a few cases

1. Fail early for invalid/zero length symbols.
2. Detect names of the form <mod:name> and skip checking for kernel
symbols in that case.

Signed-off-by: Naveen N. Rao <redacted>
---
 kernel/kallsyms.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index 6a3b249a2ae1..f7558dc5c6ac 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c

@@ -205,12 +205,20 @@ unsigned long kallsyms_lookup_name(const char *name)
 	unsigned long i;
 	unsigned int off;
 
+	if (!name || *name == '\0')
+		return 0;
+
+	/* For symbols of the form <mod>:<sym>, only check the modules */
+	if (strnchr(name, MODULE_NAME_LEN, ':'))
+		goto mod;
+
 	for (i = 0, off = 0; i < kallsyms_num_syms; i++) {
 		off = kallsyms_expand_symbol(off, namebuf, ARRAY_SIZE(namebuf));
 
 		if (strcmp(namebuf, name) == 0)
 			return kallsyms_sym_address(i);
 	}
+mod:
 	return module_kallsyms_lookup_name(name);
 }
 EXPORT_SYMBOL_GPL(kallsyms_lookup_name);

-- 
2.12.2