Since commit "modpost: do not set ->preloaded for symbols from
Module.symvers", the modpost always warns about symbols exported
multiple times.
Generally, I believe it is a good thing to show a warning when the
same symbol name is exported twice. This avoids the accidental symbol
conflict.
However, in some cases, we build an external module to provide a
different version/variant of the in-kernel module, overriding the
same set of exported symbols.
At least, there is one use-case in the upstream code;
tools/testing/nvdimm/libnvdimm.ko replaces drivers/nvdimm/libnvdimm.ko
in order to link it against mocked version of core kernel symbols.
Now, this emits a lots of 'exported twice' warnings:
https://lkml.org/lkml/2019/10/31/627
To suppress those, add a new option KBUILD_DUPLICATED_EXPORTS_NO_WARN.
If you intentionally override the existing symbols, you can pass it
from the command line:
make M=tools/testing/nvdimm KBUILD_DUPLICATED_EXPORTS_NO_WARN=1
Or, more conveniently, you can add it to the module Makefile, so
you can still do:
make M=tools/testing/nvdimm
without sprinkling the warnings.
Reported-by: Jeff Moyer <[email protected]>
Signed-off-by: Masahiro Yamada <[email protected]>
---
Jeff Moyer,
Dan Williams,
Please check if this patch solves the nvdimm build issue.
Documentation/kbuild/kbuild.rst | 7 +++++++
scripts/Makefile.modpost | 1 +
scripts/mod/modpost.c | 9 +++++++--
tools/testing/nvdimm/Kbuild | 4 ++++
4 files changed, 19 insertions(+), 2 deletions(-)
diff --git a/Documentation/kbuild/kbuild.rst b/Documentation/kbuild/kbuild.rst
index f1e5dce86af7..8ff0935f9e7f 100644
--- a/Documentation/kbuild/kbuild.rst
+++ b/Documentation/kbuild/kbuild.rst
@@ -223,6 +223,13 @@ KBUILD_SIGN_PIN
This variable allows a passphrase or PIN to be passed to the sign-file
utility when signing kernel modules, if the private key requires such.
+KBUILD_DUPLICATED_EXPORTS_NO_WARN
+---------------------------------
+This variable can be set to suppress warnings about symbols exported
+multiple times. This is useful when you are building an external module
+to provide a different version of an in-tree module.
+
+
KBUILD_MODPOST_WARN
-------------------
KBUILD_MODPOST_WARN can be set to avoid errors in case of undefined
diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost
index 8359f8af5ee6..52e50ac45688 100644
--- a/scripts/Makefile.modpost
+++ b/scripts/Makefile.modpost
@@ -53,6 +53,7 @@ MODPOST = scripts/mod/modpost \
$(if $(KBUILD_EXTMOD),$(addprefix -e ,$(KBUILD_EXTRA_SYMBOLS))) \
$(if $(KBUILD_EXTMOD),-o $(modulesymfile)) \
$(if $(CONFIG_SECTION_MISMATCH_WARN_ONLY),,-E) \
+ $(if $(KBUILD_DUPLICATED_EXPORTS_NO_WARN),-W) \
$(if $(KBUILD_MODPOST_WARN),-w)
ifdef MODPOST_VMLINUX
diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index f70b924f379f..858568f4edb4 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -33,6 +33,8 @@ static int external_module = 0;
static int vmlinux_section_warnings = 1;
/* Only warn about unresolved symbols */
static int warn_unresolved = 0;
+/* Warn about symbols exported multiple times */
+static int warn_duplicated_exports = 1;
/* How a symbol is exported */
static int sec_mismatch_count = 0;
static int sec_mismatch_fatal = 0;
@@ -382,7 +384,7 @@ static struct symbol *sym_add_exported(const char *name, struct module *mod,
if (!s) {
s = new_symbol(name, mod, export);
} else {
- if (!s->preloaded) {
+ if (warn_duplicated_exports && !s->preloaded) {
warn("%s: '%s' exported twice. Previous export was in %s%s\n",
mod->name, name, s->module->name,
is_vmlinux(s->module->name) ? "" : ".ko");
@@ -2559,7 +2561,7 @@ int main(int argc, char **argv)
struct ext_sym_list *extsym_iter;
struct ext_sym_list *extsym_start = NULL;
- while ((opt = getopt(argc, argv, "i:e:mnsT:o:awEd:")) != -1) {
+ while ((opt = getopt(argc, argv, "i:e:mnsT:o:awWEd:")) != -1) {
switch (opt) {
case 'i':
kernel_read = optarg;
@@ -2594,6 +2596,9 @@ int main(int argc, char **argv)
case 'w':
warn_unresolved = 1;
break;
+ case 'W':
+ warn_duplicated_exports = 0;
+ break;
case 'E':
sec_mismatch_fatal = 1;
break;
diff --git a/tools/testing/nvdimm/Kbuild b/tools/testing/nvdimm/Kbuild
index c4a9196d794c..c848374f3b0b 100644
--- a/tools/testing/nvdimm/Kbuild
+++ b/tools/testing/nvdimm/Kbuild
@@ -93,4 +93,8 @@ libnvdimm-y += dimm_devs.o
libnvdimm-y += libnvdimm_test.o
libnvdimm-y += config_check.o
+# This intentionally overrides the original libnvdimm.ko
+# Suppress 'exported twice' warnings from the modpost.
+KBUILD_DUPLICATED_EXPORTS_NO_WARN := 1
+
obj-m += test/
--
2.17.1
Masahiro Yamada <[email protected]> writes:
> Since commit "modpost: do not set ->preloaded for symbols from
> Module.symvers", the modpost always warns about symbols exported
> multiple times.
>
> Generally, I believe it is a good thing to show a warning when the
> same symbol name is exported twice. This avoids the accidental symbol
> conflict.
>
> However, in some cases, we build an external module to provide a
> different version/variant of the in-kernel module, overriding the
> same set of exported symbols.
>
> At least, there is one use-case in the upstream code;
> tools/testing/nvdimm/libnvdimm.ko replaces drivers/nvdimm/libnvdimm.ko
> in order to link it against mocked version of core kernel symbols.
>
> Now, this emits a lots of 'exported twice' warnings:
>
> https://lkml.org/lkml/2019/10/31/627
>
> To suppress those, add a new option KBUILD_DUPLICATED_EXPORTS_NO_WARN.
>
> If you intentionally override the existing symbols, you can pass it
> from the command line:
>
> make M=tools/testing/nvdimm KBUILD_DUPLICATED_EXPORTS_NO_WARN=1
>
> Or, more conveniently, you can add it to the module Makefile, so
> you can still do:
>
> make M=tools/testing/nvdimm
>
> without sprinkling the warnings.
>
> Reported-by: Jeff Moyer <[email protected]>
> Signed-off-by: Masahiro Yamada <[email protected]>
> ---
>
> Jeff Moyer,
> Dan Williams,
>
> Please check if this patch solves the nvdimm build issue.
Yep, that fixes it for me.
You can add:
Tested-by: Jeff Moyer <[email protected]>
Thanks!