On Mon, Jun 2, 2025 at 10:06 PM Masahiro Yamada <masahiroy@xxxxxxxxxx> wrote:
>
> In the old days, KBUILD_MODNAME was passed to C without double quotes,
> and then handled by __stringify() on the C side. This was the reason
> why KBUILD_MODNAME was mangled: characters such as commas (,) and
> hyphens (-) are not allowed in C identifiers, so they were replaced
> with underscores (_) in Kbuild.
>
> Since commit f83b5e323f57 ("kbuild: set correct KBUILD_MODNAME when
> using well known kernel symbols as module names"), KBUILD_MODNAME has
> been passed to C as a string literal, which allows any characters.
>
> Aside from this historical behavior in the build system, there is no
> longer a reason for mangling. In fact, it is rather annoying, as we
> now need to convert between hyphens and underscores in some places,
> but not in others. See commit 0267cbf297bf ("module: Account for the
> build time module name mangling").
>
> This commit eliminates that oddity, so the module name will now match
> the filename. For example, the module name of "foo-bar.ko" will be
> "foo-bar", not "foo_bar".
>
> However, this oddity persisted for so long and also affected the
> userspace. To adapt to this behavior, when a user runs "rmmod foo-bar",
> kmod converts hyphens to underscores, and passes "foo_bar" to the
> delete_module syscall.
Hmm. That was modprobe/rmmod from busybox.
kmod tries to open /sys/module/*, and
hyphen/underscore conversion happens everywhere.
libkmod: ERROR ../libkmod/libkmod-module.c:2039
kmod_module_get_holders: could not open '/sys/module/fo_o/holders': No
such file or directory
So, we may need to carry this forever...
>
> Therefore, the mod_strncmp() needs to remain in find_module_all(),
> otherwise, we cannot unload modules.
>
> Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx>
> ---
>
> kernel/module/main.c | 8 ++++++--
> scripts/Makefile.lib | 4 ++--
> 2 files changed, 8 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/module/main.c b/kernel/module/main.c
> index b8440b0887e3..1fa90a95e0c5 100644
> --- a/kernel/module/main.c
> +++ b/kernel/module/main.c
> @@ -410,7 +410,11 @@ struct module *find_module_all(const char *name, size_t len,
> lockdep_is_held(&module_mutex)) {
> if (!even_unformed && mod->state == MODULE_STATE_UNFORMED)
> continue;
> - if (strlen(mod->name) == len && !memcmp(mod->name, name, len))
> + /*
> + * For historical reasons, kmod passes a module name with
> + * a hyphen replaced with an underscore.
> + */
> + if (!mod_strncmp(mod->name, name, len))
> return mod;
> }
> return NULL;
> @@ -1135,7 +1139,7 @@ static bool module_match(const char *modname, const char *patterns)
> if (*sep)
> sep++;
>
> - if (mod_strncmp(patterns, modname, len) == 0 && (glob || len == modlen))
> + if (strncmp(patterns, modname, len) == 0 && (glob || len == modlen))
> return true;
> }
>
> diff --git a/scripts/Makefile.lib b/scripts/Makefile.lib
> index 336fb0d763c7..e37e2db5f528 100644
> --- a/scripts/Makefile.lib
> +++ b/scripts/Makefile.lib
> @@ -18,8 +18,8 @@ target-stem = $(basename $(patsubst $(obj)/%,%,$@))
> # end up in (or would, if it gets compiled in)
> name-fix-token = $(subst $(comma),_,$(subst -,_,$1))
> name-fix = $(call stringify,$(call name-fix-token,$1))
> -basename_flags = -DKBUILD_BASENAME=$(call name-fix,$(basetarget))
> -modname_flags = -DKBUILD_MODNAME=$(call name-fix,$(modname)) \
> +basename_flags = -DKBUILD_BASENAME=$(call stringify,$(basetarget))
> +modname_flags = -DKBUILD_MODNAME=$(call stringify,$(modname)) \
> -D__KBUILD_MODNAME=kmod_$(call name-fix-token,$(modname))
> modfile_flags = -DKBUILD_MODFILE=$(call stringify,$(modfile))
>
> --
> 2.43.0
>
--
Best Regards
Masahiro Yamada
