Merge patch series "Add generated modalias to modules.builtin.modinfo"

Alexey Gladkov says:

The modules.builtin.modinfo file is used by userspace (kmod to be specific) to
get information about builtin modules. Among other information about the module,
information about module aliases is stored. This is very important to determine
that a particular modalias will be handled by a module that is inside the
kernel.

There are several mechanisms for creating modalias for modules:

The first is to explicitly specify the MODULE_ALIAS of the macro. In this case,
the aliases go into the '.modinfo' section of the module if it is compiled
separately or into vmlinux.o if it is builtin into the kernel.

The second is the use of MODULE_DEVICE_TABLE followed by the use of the
modpost utility. In this case, vmlinux.o no longer has this information and
does not get it into modules.builtin.modinfo.

For example:

$ modinfo pci:v00008086d0000A36Dsv00001043sd00008694bc0Csc03i30
modinfo: ERROR: Module pci:v00008086d0000A36Dsv00001043sd00008694bc0Csc03i30 not found.

$ modinfo xhci_pci
name:           xhci_pci
filename:       (builtin)
license:        GPL
file:           drivers/usb/host/xhci-pci
description:    xHCI PCI Host Controller Driver

The builtin module is missing alias "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 add the generated by modpost modalias to
modules.builtin.modinfo. Fortunately modpost already generates .vmlinux.export.c
for exported symbols. It is possible to add `.modinfo` for builtin modules and
modify the build system so that `.modinfo` section is extracted from the
intermediate vmlinux after modpost is executed.

Link: https://patch.msgid.link/cover.1758182101.git.legion@kernel.org
Signed-off-by: Nathan Chancellor <nathan@kernel.org>

3 files changed, 47 insertions, 4 deletions

diff --git a/scripts/mod/file2alias.c b/scripts/mod/file2alias.c
index 00586119a25b..7da9735e7ab3 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__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)
@@ -1517,5 +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 5ca7c268294e..47c8aa2a6939 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -2067,11 +2067,26 @@ 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");
 
 	add_exported_symbols(&buf, mod);
+
+	buf_printf(&buf,
+		   "#include <linux/module.h>\n"
+		   "#undef __MODULE_INFO_PREFIX\n"
+		   "#define __MODULE_INFO_PREFIX\n");
+
+	list_for_each_entry_safe(alias, next, &mod->aliases, node) {
+		buf_printf(&buf, "MODULE_INFO(%s.alias, \"%s\");\n",
+			   alias->builtin_modname, alias->str);
+		list_del(&alias->node);
+		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[];
 };