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 <[email protected]>
> Signed-off-by: Boqun Feng <[email protected]>
> Signed-off-by: Miguel Ojeda <[email protected]>
> ---
> 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 <[email protected]>
> > Signed-off-by: Boqun Feng <[email protected]>
> > Signed-off-by: Miguel Ojeda <[email protected]>
> > ---
> > 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 <[email protected]>
> > > Signed-off-by: Boqun Feng <[email protected]>
> > > Signed-off-by: Miguel Ojeda <[email protected]>
> > > ---
> > > 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 <[email protected]> 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