On Thu, 27 Apr 2017 01:38:10 +0530
"Naveen N. Rao" <naveen.n....@linux.vnet.ibm.com> wrote:
> 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.
>
Looks good to me.
Reviewed-by: Masami Hiramatsu <mhira...@kernel.org>
Thanks,
> 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
>
--
Masami Hiramatsu <mhira...@kernel.org>
