linux-kernel - Re: [PATCH] kallsyms: optimize kallsyms_lookup

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Message-ID: <87lgqn1m8k.fsf@concordia.ellerman.id.au>
Date:   Wed, 26 Apr 2017 20:44:59 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
Cc:     Masami Hiramatsu <mhiramat@...nel.org>,
        Paul Clarke <pc@...ibm.com>,
        David Laight <David.Laight@...LAB.COM>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH] kallsyms: optimize kallsyms_lookup_name() for a few cases

"Naveen N. Rao" <naveen.n.rao@...ux.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.

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.

cheers