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@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index cdd9098b603533f86e5fe1fb3c696feb2af70815..841f694752479ef54bfe290b7593262391d87fb7 100644 (file)
--- 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;
        }