linux-kernel - [PATCH 04/27] modpost: add a separate error for exported symbols without definition

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Message-Id: <20220424190811.1678416-5-masahiroy@kernel.org>
Date:   Mon, 25 Apr 2022 04:07:48 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     linux-kbuild@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org,
        Masahiro Yamada <masahiroy@...nel.org>,
        Michal Marek <michal.lkml@...kovi.net>,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: [PATCH 04/27] modpost: add a separate error for exported symbols without definition

It took me a while to understand the intent of "exp->module == mod".

This code goes back to 2003 (pre-git era).

The commit is not in this git repository, and might be worth a little
explanation.

You can add EXPORT_SYMBOL() with no definition in the same file (but you
need to put a declaration).

  int foo(void);
  EXPORT_SYMBOL(foo);

This is typical when EXPORT_SYMBOL() is defined in a C file, but the
actual implementation is in a separate assembly file. In old days,
EXPORT_SYMBOL() were only available in C files (but this limitation
does not exist any more).

Add a separate, clearer message if an exported symbol has no definition.
It should be an error even if KBUILD_MODPOST_WARN is given.

[1]: https://git.kernel.org/pub/scm/linux/kernel/git/history/history.git/commit/?id=2763b6bcb96e6a38a2fe31108fe5759ec5bcc80a

Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
---

 scripts/mod/modpost.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index c7cfeeb088f7..969a081dba62 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -2147,13 +2147,18 @@ static void check_exports(struct module *mod)
 	for (s = mod->unres; s; s = s->next) {
 		const char *basename;
 		exp = find_symbol(s->name);
-		if (!exp || exp->module == mod) {
+		if (!exp) {
 			if (!s->weak && nr_unresolved++ < MAX_UNRESOLVED_REPORTS)
 				modpost_log(warn_unresolved ? LOG_WARN : LOG_ERROR,
 					    "\"%s\" [%s.ko] undefined!\n",
 					    s->name, mod->name);
 			continue;
 		}
+		if (exp->module == mod) {
+			error("\"%s\" [%s.ko] was exported without definition\n",
+			      s->name, mod->name);
+			continue;
+		}
 		basename = strrchr(mod->name, '/');
 		if (basename)
 			basename++;
-- 
2.32.0