linux-kernel - [PATCH v2 11/26] modpost: make multiple export error

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Date:   Sun,  1 May 2022 17:40:17 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     linux-kbuild@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org,
        Masahiro Yamada <masahiroy@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Michal Marek <michal.lkml@...kovi.net>
Subject: [PATCH v2 11/26] modpost: make multiple export error

This is currently a warning, but I think modpost should stop building
in this case.

If the same symbol is exported multiple times and we let it keep going,
the sanity check becomes difficult.

Only the legitimate case is that an external module overrides the
corresponding in-tree module to provide a different implementation
with the same interface.

Also, there exists an upstream example that exploits this feature.

  $ make M=tools/testing/nvdimm

... builds tools/testing/nvdimm/libnvdimm.ko. This is a mocked module
that overrides the symbols from drivers/nvdimm/libnvdimm.ko.

Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>
---

Changes in v2:
  - Add more commit description

 scripts/mod/modpost.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index 4ce8d164b8e0..1f01fc942f94 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -417,9 +417,9 @@ static struct symbol *sym_add_exported(const char *name, struct module *mod,
 		list_add_tail(&s->list, &mod->exported_symbols);
 	} else if (!external_module || s->module->is_vmlinux ||
 		   s->module == mod) {
-		warn("%s: '%s' exported twice. Previous export was in %s%s\n",
-		     mod->name, name, s->module->name,
-		     s->module->is_vmlinux ? "" : ".ko");
+		error("%s: '%s' exported twice. Previous export was in %s%s\n",
+		      mod->name, name, s->module->name,
+		      s->module->is_vmlinux ? "" : ".ko");
 		return s;
 	}
 
-- 
2.32.0