This adds a static assert to ensure `KSYM_NAME_LEN_BUFFER`
gets updated when `KSYM_NAME_LEN` changes.

The relationship used is one that keeps the new size (512+1)
close to the original buffer size (500).

Co-developed-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
---
 scripts/kallsyms.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
index f3c5a2623f71..f543b1c4f99f 100644
--- a/scripts/kallsyms.c
+++ b/scripts/kallsyms.c
@@ -33,7 +33,11 @@
 #define KSYM_NAME_LEN		128
 
 /* A substantially bigger size than the current maximum. */
-#define KSYM_NAME_LEN_BUFFER	499
+#define KSYM_NAME_LEN_BUFFER	512
+_Static_assert(
+	KSYM_NAME_LEN_BUFFER == KSYM_NAME_LEN * 4,
+	"Please keep KSYM_NAME_LEN_BUFFER in sync with KSYM_NAME_LEN"
+);
 
 struct sym_entry {
 	unsigned long long addr;
-- 
2.37.1

On Fri, Aug 05, 2022 at 05:41:48PM +0200, Miguel Ojeda wrote:
> This adds a static assert to ensure `KSYM_NAME_LEN_BUFFER`
> gets updated when `KSYM_NAME_LEN` changes.
> 
> The relationship used is one that keeps the new size (512+1)
> close to the original buffer size (500).
> 
> Co-developed-by: Boqun Feng <boqun.feng@gmail.com>
> Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
> Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
> ---
>  scripts/kallsyms.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
> index f3c5a2623f71..f543b1c4f99f 100644
> --- a/scripts/kallsyms.c
> +++ b/scripts/kallsyms.c
> @@ -33,7 +33,11 @@
>  #define KSYM_NAME_LEN		128
>  
>  /* A substantially bigger size than the current maximum. */
> -#define KSYM_NAME_LEN_BUFFER	499
> +#define KSYM_NAME_LEN_BUFFER	512
> +_Static_assert(
> +	KSYM_NAME_LEN_BUFFER == KSYM_NAME_LEN * 4,
> +	"Please keep KSYM_NAME_LEN_BUFFER in sync with KSYM_NAME_LEN"
> +);

Why not just make this define:

#define KSYM_NAME_LEN_BUFFER (KSYM_NAME_LEN * 4)

? If there's a good reason not it, please put it in the commit log.

-Kees

-- 
Kees Cook

On Wed, Aug 17, 2022 at 12:39:48PM -0700, Kees Cook wrote:
> On Fri, Aug 05, 2022 at 05:41:48PM +0200, Miguel Ojeda wrote:
> > This adds a static assert to ensure `KSYM_NAME_LEN_BUFFER`
> > gets updated when `KSYM_NAME_LEN` changes.
> > 
> > The relationship used is one that keeps the new size (512+1)
> > close to the original buffer size (500).
> > 
> > Co-developed-by: Boqun Feng <boqun.feng@gmail.com>
> > Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
> > Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
> > ---
> >  scripts/kallsyms.c | 6 +++++-
> >  1 file changed, 5 insertions(+), 1 deletion(-)
> > 
> > diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
> > index f3c5a2623f71..f543b1c4f99f 100644
> > --- a/scripts/kallsyms.c
> > +++ b/scripts/kallsyms.c
> > @@ -33,7 +33,11 @@
> >  #define KSYM_NAME_LEN		128
> >  
> >  /* A substantially bigger size than the current maximum. */
> > -#define KSYM_NAME_LEN_BUFFER	499
> > +#define KSYM_NAME_LEN_BUFFER	512
> > +_Static_assert(
> > +	KSYM_NAME_LEN_BUFFER == KSYM_NAME_LEN * 4,
> > +	"Please keep KSYM_NAME_LEN_BUFFER in sync with KSYM_NAME_LEN"
> > +);
> 
> Why not just make this define:
> 
> #define KSYM_NAME_LEN_BUFFER (KSYM_NAME_LEN * 4)
> 
> ? If there's a good reason not it, please put it in the commit log.
> 

Because KSYM_NAME_LEN_BUFFER is used as a string by stringify() in
fscanf(), defining it as (KSYM_NAME_LEN * 4) will produce a string

	"128 * 4"

after stringify() and that doesn't work with fscanf().

Miguel, maybe we can add something below in the commit log?

`KSYM_NAME_LEN_BUFFER` cannot be defined as an expression, because it
gets stringified in the fscanf() format. Therefore a _Static_assert() is
needed.

Thoughts?

Regards,
Boqun

> -Kees
> 
> -- 
> Kees Cook

On Wed, Aug 17, 2022 at 12:50:50PM -0700, Boqun Feng wrote:
> On Wed, Aug 17, 2022 at 12:39:48PM -0700, Kees Cook wrote:
> > On Fri, Aug 05, 2022 at 05:41:48PM +0200, Miguel Ojeda wrote:
> > > This adds a static assert to ensure `KSYM_NAME_LEN_BUFFER`
> > > gets updated when `KSYM_NAME_LEN` changes.
> > > 
> > > The relationship used is one that keeps the new size (512+1)
> > > close to the original buffer size (500).
> > > 
> > > Co-developed-by: Boqun Feng <boqun.feng@gmail.com>
> > > Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
> > > Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
> > > ---
> > >  scripts/kallsyms.c | 6 +++++-
> > >  1 file changed, 5 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
> > > index f3c5a2623f71..f543b1c4f99f 100644
> > > --- a/scripts/kallsyms.c
> > > +++ b/scripts/kallsyms.c
> > > @@ -33,7 +33,11 @@
> > >  #define KSYM_NAME_LEN		128
> > >  
> > >  /* A substantially bigger size than the current maximum. */
> > > -#define KSYM_NAME_LEN_BUFFER	499
> > > +#define KSYM_NAME_LEN_BUFFER	512
> > > +_Static_assert(
> > > +	KSYM_NAME_LEN_BUFFER == KSYM_NAME_LEN * 4,
> > > +	"Please keep KSYM_NAME_LEN_BUFFER in sync with KSYM_NAME_LEN"
> > > +);
> > 
> > Why not just make this define:
> > 
> > #define KSYM_NAME_LEN_BUFFER (KSYM_NAME_LEN * 4)
> > 
> > ? If there's a good reason not it, please put it in the commit log.
> > 
> 
> Because KSYM_NAME_LEN_BUFFER is used as a string by stringify() in
> fscanf(), defining it as (KSYM_NAME_LEN * 4) will produce a string
> 
> 	"128 * 4"
> 
> after stringify() and that doesn't work with fscanf().

Ah yeah. Thanks!

> Miguel, maybe we can add something below in the commit log?
> 
> `KSYM_NAME_LEN_BUFFER` cannot be defined as an expression, because it
> gets stringified in the fscanf() format. Therefore a _Static_assert() is
> needed.

Yeah, please add a source comment for that. :)

-- 
Kees Cook

On Wed, Aug 17, 2022 at 10:31 PM Kees Cook <keescook@chromium.org> wrote:
>
> Yeah, please add a source comment for that. :)

I agree, I think this sort of explanation should be in the source vs.
the commit message, since it explains something about the code, not
the change itself.

Cheers,
Miguel