Re: [PATCH v2 5/7] modpost: Create modalias for builtin modules

[Masahiro Yamada]

On Mon, May 5, 2025 at 6:39 PM Alexey Gladkov <legion@xxxxxxxxxx> wrote:
>
> For some modules, modalias is generated using the modpost utility and
> the section is added to the module file.
>
> When a module is added inside vmlinux, modpost does not generate
> modalias for such modules and the information is lost.
>
> As a result kmod (which uses modules.builtin.modinfo in userspace)
> cannot determine that modalias is handled by a builtin kernel module.
>
> $ cat /sys/devices/pci0000:00/0000:00:14.0/modalias
> pci:v00008086d0000A36Dsv00001043sd00008694bc0Csc03i30
>
> $ modinfo xhci_pci
> name:           xhci_pci
> filename:       (builtin)
> license:        GPL
> file:           drivers/usb/host/xhci-pci
> description:    xHCI PCI Host Controller Driver
>
> Missing modalias "pci:v*d*sv*sd*bc0Csc03i30*" which will be generated by
> modpost if the module is built separately.
>
> To fix this it is necessary to generate the same modalias for vmlinux as
> for the individual modules. Fortunately '.vmlinux.export.o' is already
> generated from which '.modinfo' can be extracted in the same way as for
> vmlinux.o.
>
> Signed-off-by: Alexey Gladkov <legion@xxxxxxxxxx>
> ---
>
> v2: As Petr Pavlu suggested, I separated the builtin modules from the external
>     modules. I've also added a search for duplicate modules.
>



> ---
>  include/linux/module.h   |  4 ----
>  scripts/mod/file2alias.c |  5 +++++
>  scripts/mod/modpost.c    | 35 +++++++++++++++++++++++++++--------
>  scripts/mod/modpost.h    | 15 ++++++++++++++-
>  4 files changed, 46 insertions(+), 13 deletions(-)


I can implement this with less code change.

I attached my patch.






-- 
Best Regards
Masahiro Yamada
From 28b8431db696b15a5812d6ca0a7372a30e060cfb Mon Sep 17 00:00:00 2001
From: Masahiro Yamada <masahiroy@xxxxxxxxxx>
Date: Fri, 9 May 2025 00:22:46 +0900
Subject: [PATCH] Another simple implementation

Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx>
---
 include/linux/module.h   |  4 ----
 scripts/mod/file2alias.c | 16 ++++++++++++++++
 scripts/mod/modpost.c    | 14 +++++++++++++-
 scripts/mod/modpost.h    |  2 ++
 4 files changed, 31 insertions(+), 5 deletions(-)

diff --git a/include/linux/module.h b/include/linux/module.h
index 01fceca47a5b..17e69e4a1802 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -259,14 +259,10 @@ struct module_kobject *lookup_or_create_module_kobject(const char *name);
 	__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)	\
   __attribute__ ((unused, alias(__stringify(name))))
-#else  /* !MODULE */
-#define MODULE_DEVICE_TABLE(type, name)
-#endif
 
 /* Version of form [<epoch>:]<version>[-<extra-version>].
  * Or for CVS/RCS ID version, everything but the number is stripped.
diff --git a/scripts/mod/file2alias.c b/scripts/mod/file2alias.c
index dff1799a4c79..d42f2c742fd6 100644
--- a/scripts/mod/file2alias.c
+++ b/scripts/mod/file2alias.c
@@ -1527,5 +1527,21 @@ void handle_moddevtable(struct module *mod, struct elf_info *info,
 		}
 	}
 
+	if (mod->is_vmlinux) {
+		struct module_alias *alias;
+
+		/*
+		 * If this is vmlinux, record the name of the builtin module.
+		 * Traverse the linked list in the reverse order, and set the
+		 * builtin_modname unless it has already been set in the
+		 * previous call.
+		 */
+		list_for_each_entry_reverse(alias, &mod->aliases, node) {
+			if (alias->builtin_modname)
+				break;
+			alias->builtin_modname = xstrndup(modname, modnamelen);
+		}
+	}
+
 	free(zeros);
 }
diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index be89921d60b6..285b6c20c760 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -2021,11 +2021,23 @@ static void write_if_changed(struct buffer *b, const char *fname)
 static void write_vmlinux_export_c_file(struct module *mod)
 {
 	struct buffer buf = { };
+	struct module_alias *alias, *next;
 
 	buf_printf(&buf,
-		   "#include <linux/export-internal.h>\n");
+		   "#include <linux/export-internal.h>\n"
+		   "#include <linux/module.h>\n");
 
 	add_exported_symbols(&buf, mod);
+
+	list_for_each_entry_safe(alias, next, &mod->aliases, node) {
+		buf_printf(&buf, "MODULE_ALIAS_MODNAME(\"%s\", \"%s\");\n",
+			   alias->builtin_modname, alias->str);
+		list_del(&alias->node);
+		printf("builtin modname = %s\n", alias->builtin_modname);
+		free(alias->builtin_modname);
+		free(alias);
+	}
+
 	write_if_changed(&buf, ".vmlinux.export.c");
 	free(buf.p);
 }
diff --git a/scripts/mod/modpost.h b/scripts/mod/modpost.h
index 9133e4c3803f..2aecb8f25c87 100644
--- a/scripts/mod/modpost.h
+++ b/scripts/mod/modpost.h
@@ -99,10 +99,12 @@ buf_write(struct buffer *buf, const char *s, int len);
  * struct module_alias - auto-generated MODULE_ALIAS()
  *
  * @node: linked to module::aliases
+ * @modname: name of the builtin module (only for vmlinux)
  * @str: a string for MODULE_ALIAS()
  */
 struct module_alias {
 	struct list_head node;
+	char *builtin_modname;
 	char str[];
 };
 
-- 
2.43.0