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

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Message-ID: <20250602130609.402581-1-masahiroy@kernel.org>
Date: Mon,  2 Jun 2025 22:06:02 +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>,
	Masahiro Yamada <masahiroy@...nel.org>,
	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: [PATCH] kbuild: stop module name mangling

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.

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