linux-kernel - Re: [PATCH] kbuild: stop module name mangling

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Message-ID: <CAK7LNATBCmhf_yT+1nkULwRZgQ3QJ6PDbUSWAPOvYZT478M07A@mail.gmail.com>
Date: Tue, 3 Jun 2025 04:00:30 +0900
From: Masahiro Yamada <masahiroy@...nel.org>
To: linux-kbuild@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>, 
	Lucas De Marchi <lucas.de.marchi@...il.com>, Daniel Gomez <da.gomez@...sung.com>, 
	Luis Chamberlain <mcgrof@...nel.org>, Nathan Chancellor <nathan@...nel.org>, 
	Nicolas Schier <nicolas.schier@...ux.dev>, Petr Pavlu <petr.pavlu@...e.com>, 
	Sami Tolvanen <samitolvanen@...gle.com>, linux-modules@...r.kernel.org
Subject: Re: [PATCH] kbuild: stop module name mangling

On Mon, Jun 2, 2025 at 10:06 PM Masahiro Yamada <masahiroy@...nel.org> 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@...nel.org>
> ---
>
>  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