Michael Ellerman wrote:
> "Naveen N. Rao" <naveen.n....@linux.vnet.ibm.com> writes:
>> 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 <naveen.n....@linux.vnet.ibm.com>
---
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
