Re: [PATCH 1/3] module: deal with alignment issues in built-in module versions

[Geert Uytterhoeven]

On Mon, Feb 21, 2011 at 05:00, Rusty Russell <rusty@xxxxxxxxxxxxxxx> wrote:
>> Except that .long is 32-bit on ppc64 :-( You need .llong for 64-bit.
>
> OK, all options suck. ÂDo we want the workaround or not?

We can discuss about that until someone gets bitten by that.

But please fix the "aligned(sizeof(void *))"-in-one-place-only issue.

> Cheers,
> Rusty.
>
> Subject: module: deal with alignment issues in built-in module versions
> Date: Mon, 7 Feb 2011 16:02:25 -0800
> From: Dmitry Torokhov <dtor@xxxxxxxxxx>
>
> On m68k natural alignment is 2-byte boundary but we are trying to
> align structures in __modver section on sizeof(void *) boundary.
> This causes trouble when we try to access elements in this section
> in array-like fashion when create "version" attributes for built-in
> modules.
>
> Moreover, as DaveM said, we can't reliably put structures into
> independent objects, put them into a special section, and then expect
> array access over them (via the section boundaries) after linking the
> objects together to just "work" due to variable alignment choices in
> different situations. The only solution that seems to work reliably
> is to make an array of plain pointers to the objects in question and
> put those pointers in the special section.
>
> Reported-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
> Signed-off-by: Dmitry Torokhov <dtor@xxxxxxxxxx>
> Signed-off-by: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
> ---
> Âinclude/linux/module.h | Â 10 +++++-----
> Âkernel/params.c    Â|  Â9 ++++++---
> Â2 files changed, 11 insertions(+), 8 deletions(-)
>
> diff --git a/include/linux/module.h b/include/linux/module.h
> index 9bdf27c..9b7081a 100644
> --- a/include/linux/module.h
> +++ b/include/linux/module.h
> @@ -174,10 +174,7 @@ extern struct module __this_module;
> Â#define MODULE_VERSION(_version) Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â \
> Â Â Â Âextern ssize_t __modver_version_show(struct module_attribute *, \
> Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â struct module *, char *); Â\
> -    static struct module_version_attribute __modver_version_attr  Â\
> -    __used                             Â\
> - Â Â__attribute__ ((__section__ ("__modver"),aligned(sizeof(void *)))) \
> - Â Â Â = { Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â \
> + Â Â Â static struct module_version_attribute ___modver_attr = { Â Â Â \
> Â Â Â Â Â Â Â Â.mattr Â= { Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â \
>            Â.attr  = {                   \
>                Â.name  = "version",          Â\
> @@ -187,7 +184,10 @@ extern struct module __this_module;
> Â Â Â Â Â Â Â Â}, Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â\
>        Â.module_name  Â= KBUILD_MODNAME,            \
>        Â.version    Â= _version,               \
> - Â Â Â }
> + Â Â Â }; Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â\
> +    static const struct module_version_attribute          Â\
> + Â Â Â __used __attribute__ ((__section__ ("__modver"))) Â Â Â Â Â Â Â \
> + Â Â Â * __moduleparam_const __modver_attr = &___modver_attr
> Â#endif
>
> Â/* Optional firmware file (or files) needed by the module
> diff --git a/kernel/params.c b/kernel/params.c
> index 0da1411..09a08cb 100644
> --- a/kernel/params.c
> +++ b/kernel/params.c
> @@ -821,15 +821,18 @@ ssize_t __modver_version_show(struct module_attribute *mattr,
> Â Â Â Âreturn sprintf(buf, "%s\n", vattr->version);
> Â}
>
> -extern struct module_version_attribute __start___modver[], __stop___modver[];
> +extern const struct module_version_attribute *__start___modver[];
> +extern const struct module_version_attribute *__stop___modver[];
>
> Âstatic void __init version_sysfs_builtin(void)
> Â{
> - Â Â Â const struct module_version_attribute *vattr;
> + Â Â Â const struct module_version_attribute **p;
> Â Â Â Âstruct module_kobject *mk;
> Â Â Â Âint err;
>
> - Â Â Â for (vattr = __start___modver; vattr < __stop___modver; vattr++) {
> + Â Â Â for (p = __start___modver; p < __stop___modver; p++) {
> + Â Â Â Â Â Â Â const struct module_version_attribute *vattr = *p;
> +
> Â Â Â Â Â Â Â Âmk = locate_module_kobject(vattr->module_name);
> Â Â Â Â Â Â Â Âif (mk) {
> Â Â Â Â Â Â Â Â Â Â Â Âerr = sysfs_create_file(&mk->kobj, &vattr->mattr.attr);

Gr{oetje,eeting}s,

            Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
             Â Â -- Linus Torvalds
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/