Re: git: 005aa1743b42 - main - modules: bzero the modspecific_t

On Sat, Jul 1, 2023 at 7:13 PM Konstantin Belousov <kostikbel@gmail.com>
wrote:

> On Sat, Jul 01, 2023 at 10:59:22PM +0000, Ka Ho Ng wrote:
> > The branch main has been updated by khng:
> >
> > URL:
> https://cgit.FreeBSD.org/src/commit/?id=005aa1743b42b52fbd49b9d5ec44816902b6ee9f
> >
> > commit 005aa1743b42b52fbd49b9d5ec44816902b6ee9f
> > Author:     Ka Ho Ng <khng@FreeBSD.org>
> > AuthorDate: 2023-07-01 19:41:53 +0000
> > Commit:     Ka Ho Ng <khng@FreeBSD.org>
> > CommitDate: 2023-07-01 22:58:46 +0000
> >
> >     modules: bzero the modspecific_t
> >
> >     Per https://reviews.llvm.org/D68115, only the first field is
> >     zero-initialized, meanwhile other fields are undef.
> This is not true.
>
> >
> >     The pattern can be observed on clang as well, that when
> >     -ftrivial-auto-var-init=pattern is specified 0xaa is filled for
> >     non-active fields, otherwise they are zero-initialized.
> What are non-active fields?
> All fields with implicit initializers
> "shall be initialized implicitly the same as
> objects that have static storage duration."
>
> I do not think this is required for padding.
>
In that case, modspecific_t ms did become 0xaaaaaaaa00000000 on amd64 if
-ftrivial-auto-var-init=pattern was specified.


>
> >     Technically both are acceptable when using clang. However it
> >     would be good to simply bzero the modspecific_t in such case to
> >     be strict to the standard.
> >
> >     MFC with:       2cab2d43b83b
> >     MFC after:      1 day
> Min MFC period is 3 days.
>
> >     Sponsored by:   Juniper Networks, Inc.
> >     Reviewed by:    delphij
> >     Differential Revision:  https://reviews.freebsd.org/D40830
> > ---
> >  sys/kern/kern_syscalls.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/sys/kern/kern_syscalls.c b/sys/kern/kern_syscalls.c
> > index 234e51cfd280..0b51edf5e985 100644
> > --- a/sys/kern/kern_syscalls.c
> > +++ b/sys/kern/kern_syscalls.c
> > @@ -173,9 +173,10 @@ kern_syscall_module_handler(struct sysent *sysents,
> struct module *mod,
> >      int what, void *arg)
> >  {
> >       struct syscall_module_data *data = arg;
> > -     modspecific_t ms = { 0 };
> > +     modspecific_t ms;
> >       int error;
> >
> > +     bzero(&ms, sizeof(ms));
> >       switch (what) {
> >       case MOD_LOAD:
> >               error = kern_syscall_register(sysents, data->offset,


Ka Ho