On Thu, Sep 26, 2024 at 5:22 AM Christophe Leroy
<christophe.leroy@xxxxxxxxxx> wrote:
>
>
>
> Le 26/09/2024 à 01:38, Matthew Maurer a écrit :
> > Adds a new format for MODVERSIONS which stores each field in a separate
> > ELF section. This initially adds support for variable length names, but
> > could later be used to add additional fields to MODVERSIONS in a
> > backwards compatible way if needed. Any new fields will be ignored by
> > old user tooling, unlike the current format where user tooling cannot
> > tolerate adjustments to the format (for example making the name field
> > longer).
> >
> > Since PPC munges its version records to strip leading dots, we reproduce
> > the munging for the new format. Other architectures do not appear to
> > have architecture-specific usage of this information.
> >
> > Signed-off-by: Matthew Maurer <mmaurer@xxxxxxxxxx>
> > ---
> > arch/powerpc/kernel/module_64.c | 23 ++++++++-
> > kernel/module/internal.h | 11 ++++
> > kernel/module/main.c | 92 ++++++++++++++++++++++++++++++---
> > kernel/module/version.c | 45 ++++++++++++++++
> > 4 files changed, 161 insertions(+), 10 deletions(-)
> >
> > diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
> > index e9bab599d0c2..4e7b156dd8b2 100644
> > --- a/arch/powerpc/kernel/module_64.c
> > +++ b/arch/powerpc/kernel/module_64.c
> > @@ -355,6 +355,23 @@ static void dedotify_versions(struct modversion_info *vers,
> > }
> > }
> >
> > +static void dedotify_ext_version_names(char *str_seq, unsigned long size)
> > +{
> > + unsigned long out = 0;
> > + unsigned long in;
> > + char last = '\0';
> > +
> > + for (in = 0; in < size; in++) {
> > + /* Skip one leading dot */
> > + if (last == '\0' && str_seq[in] == '.')
> > + in++;
> > + last = str_seq[in];
> > + str_seq[out++] = last;
> > + }
>
> Why do you need a loop here ?
>
> Can't you just do something like:
>
> if (str_seq[0] == '.')
> memmove(str_seq, str_seq + 1, size);
I initially had the same thought, but it's because this is is a
sequence of multiple null-terminated strings, and we need to dedotify
all of them, not just the first one. Here's an example:
https://godbolt.org/z/avMGnd48M
> > + /* Zero the trailing portion of the names table for robustness */
> > + memset(&str_seq[out], 0, size - out);
>
> This seems unneeded.
Strictly speaking it shouldn't be needed, but I think it's still good
hygiene to not leave another null-terminated fragment at the end.
Sami
