Re: [PATCH v3 3/6] modpost: Make mod_device_table aliases more unique

[Masahiro Yamada]

On Tue, May 27, 2025 at 6:08 PM Alexey Gladkov <legion@xxxxxxxxxx> wrote:
>
> In order to avoid symbol conflicts if they appear in the same binary, a
> more unique alias identifier can be generated.

Why must this be unique?

What problem would happen if the same symbol names
appear in MODULE_DEVICE_TABLE()?


>
> Signed-off-by: Alexey Gladkov <legion@xxxxxxxxxx>
> Reviewed-by: Petr Pavlu <petr.pavlu@xxxxxxxx>
> ---
>  include/linux/module.h   | 14 ++++++++++++--
>  scripts/mod/file2alias.c | 18 ++++++++++++++----
>  2 files changed, 26 insertions(+), 6 deletions(-)
>
> diff --git a/include/linux/module.h b/include/linux/module.h
> index 88048561360f..e7506684069d 100644
> --- a/include/linux/module.h
> +++ b/include/linux/module.h
> @@ -249,10 +249,20 @@ struct module_kobject *lookup_or_create_module_kobject(const char *name);
>  /* What your module does. */
>  #define MODULE_DESCRIPTION(_description) MODULE_INFO(description, _description)
>
> +/* Format: __mod_device_table__<counter>__kmod_<modname>__<type>__<name> */
> +#define __mod_device_table(type, name) \
> +       __PASTE(__mod_device_table__,   \
> +       __PASTE(__COUNTER__,            \
> +       __PASTE(__,                     \
> +       __PASTE(__KBUILD_MODNAME,       \
> +       __PASTE(__,                     \
> +       __PASTE(type,                   \
> +       __PASTE(__, name)))))))
> +
>  #ifdef MODULE
>  /* Creates an alias so file2alias.c can find device table. */
> -#define MODULE_DEVICE_TABLE(type, name)                                        \
> -extern typeof(name) __mod_device_table__##type##__##name               \
> +#define MODULE_DEVICE_TABLE(type, name)                        \
> +extern typeof(name) __mod_device_table(type, name)     \
>    __attribute__ ((unused, alias(__stringify(name))))
>  #else  /* !MODULE */
>  #define MODULE_DEVICE_TABLE(type, name)
> diff --git a/scripts/mod/file2alias.c b/scripts/mod/file2alias.c
> index 00586119a25b..dff1799a4c79 100644
> --- a/scripts/mod/file2alias.c
> +++ b/scripts/mod/file2alias.c
> @@ -1476,8 +1476,8 @@ void handle_moddevtable(struct module *mod, struct elf_info *info,
>  {
>         void *symval;
>         char *zeros = NULL;
> -       const char *type, *name;
> -       size_t typelen;
> +       const char *type, *name, *modname;
> +       size_t typelen, modnamelen;
>         static const char *prefix = "__mod_device_table__";
>
>         /* We're looking for a section relative symbol */
> @@ -1488,10 +1488,20 @@ void handle_moddevtable(struct module *mod, struct elf_info *info,
>         if (ELF_ST_TYPE(sym->st_info) != STT_OBJECT)
>                 return;
>
> -       /* All our symbols are of form __mod_device_table__<type>__<name>. */
> +       /* All our symbols are of form __mod_device_table__<counter>__kmod_<modname>__<type>__<name>. */
>         if (!strstarts(symname, prefix))
>                 return;
> -       type = symname + strlen(prefix);
> +
> +       modname = strstr(symname, "__kmod_");
> +       if (!modname)
> +               return;
> +       modname += strlen("__kmod_");
> +
> +       type = strstr(modname, "__");
> +       if (!type)
> +               return;
> +       modnamelen = type - modname;
> +       type += strlen("__");
>
>         name = strstr(type, "__");
>         if (!name)
> --
> 2.49.0
>


-- 
Best Regards
Masahiro Yamada