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charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Sun, Jul 2, 2023 at 6:03=E2=80=AFAM Ka Ho Ng wrote: > On Sat, Jul 1, 2023 at 7:13=E2=80=AFPM Konstantin Belousov > 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=3D005aa1743b42b52fbd49b9d5ec4481= 6902b6ee9f >> > >> > commit 005aa1743b42b52fbd49b9d5ec44816902b6ee9f >> > Author: Ka Ho Ng >> > AuthorDate: 2023-07-01 19:41:53 +0000 >> > Commit: Ka Ho Ng >> > 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=3Dpattern 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=3Dpattern 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 =3D arg; >> > - modspecific_t ms =3D { 0 }; >> > + modspecific_t ms; >> > int error; >> > >> > + bzero(&ms, sizeof(ms)); >> > switch (what) { >> > case MOD_LOAD: >> > error =3D kern_syscall_register(sysents, data->offset, > > > Ka Ho > Since I missed the reply-all button just now, I resend this email. Reading on N2716 one of the footnote stated: "Note that aggregate type does not include union type because an object with union type can only contain one member at a time" And below at 6.7.9.21 only aggregate was mentioned but not union, which matched what I observed with an `cc -ftrivial-auto-var-init=3Dpattern` invocation. Ka Ho --0000000000000c84c705ff7e6065 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
On Sun, Jul 2, 2023 at 6:03=E2=80=AFAM Ka= Ho Ng <khng300@gmail.com> w= rote:
On Sat, Jul 1, 2023 at 7= :13=E2=80=AFPM 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=3D005aa1743b42b52fbd49b9d5ec44816902b6ee9f<= /a>
>
> commit 005aa1743b42b52fbd49b9d5ec44816902b6ee9f
> Author:=C2=A0 =C2=A0 =C2=A0Ka Ho Ng <khng@FreeBSD.org>
> AuthorDate: 2023-07-01 19:41:53 +0000
> Commit:=C2=A0 =C2=A0 =C2=A0Ka Ho Ng <khng@FreeBSD.org>
> CommitDate: 2023-07-01 22:58:46 +0000
>
>=C2=A0 =C2=A0 =C2=A0modules: bzero the modspecific_t
>=C2=A0 =C2=A0 =C2=A0
>=C2=A0 =C2=A0 =C2=A0Per https://reviews.llvm.org/D68115, only= the first field is
>=C2=A0 =C2=A0 =C2=A0zero-initialized, meanwhile other fields are undef.=
This is not true.

>=C2=A0 =C2=A0 =C2=A0
>=C2=A0 =C2=A0 =C2=A0The pattern can be observed on clang as well, that = when
>=C2=A0 =C2=A0 =C2=A0-ftrivial-auto-var-init=3Dpattern is specified 0xaa= is filled for
>=C2=A0 =C2=A0 =C2=A0non-active fields, otherwise they are zero-initiali= zed.
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 c= ase, modspecific_t ms did become 0xaaaaaaaa00000000 on amd64 if -ftrivial-a= uto-var-init=3Dpattern was specified.
=C2=A0

>=C2=A0 =C2=A0 =C2=A0Technically both are acceptable when using clang. H= owever it
>=C2=A0 =C2=A0 =C2=A0would be good to simply bzero the modspecific_t in = such case to
>=C2=A0 =C2=A0 =C2=A0be strict to the standard.
>=C2=A0 =C2=A0 =C2=A0
>=C2=A0 =C2=A0 =C2=A0MFC with:=C2=A0 =C2=A0 =C2=A0 =C2=A02cab2d43b83b >=C2=A0 =C2=A0 =C2=A0MFC after:=C2=A0 =C2=A0 =C2=A0 1 day
Min MFC period is 3 days.

>=C2=A0 =C2=A0 =C2=A0Sponsored by:=C2=A0 =C2=A0Juniper Networks, Inc. >=C2=A0 =C2=A0 =C2=A0Reviewed by:=C2=A0 =C2=A0 delphij
>=C2=A0 =C2=A0 =C2=A0Differential Revision:=C2=A0 https://revie= ws.freebsd.org/D40830
> ---
>=C2=A0 sys/kern/kern_syscalls.c | 3 ++-
>=C2=A0 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 *sysent= s, struct module *mod,
>=C2=A0 =C2=A0 =C2=A0 int what, void *arg)
>=C2=A0 {
>=C2=A0 =C2=A0 =C2=A0 =C2=A0struct syscall_module_data *data =3D arg; > -=C2=A0 =C2=A0 =C2=A0modspecific_t ms =3D { 0 };
> +=C2=A0 =C2=A0 =C2=A0modspecific_t ms;
>=C2=A0 =C2=A0 =C2=A0 =C2=A0int error;
>=C2=A0
> +=C2=A0 =C2=A0 =C2=A0bzero(&ms, sizeof(ms));
>=C2=A0 =C2=A0 =C2=A0 =C2=A0switch (what) {
>=C2=A0 =C2=A0 =C2=A0 =C2=A0case MOD_LOAD:
>=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0error =3D kern_s= yscall_register(sysents, data->offset,

K= a Ho
Since I missed the reply-all button= just now, I resend this=C2=A0email.

Reading on N2= 716 one of the footnote stated:
"Note that aggregate type does not = include union type because an object with union type can only contain one m= ember at a time"

And below at 6.7.9.21 only aggregat= e was mentioned but not union, which matched what I observed with an `cc -f= trivial-auto-var-init=3Dpattern` invocation.

Ka Ho= =C2=A0
--0000000000000c84c705ff7e6065--