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 <jmoyer@xxxxxxxxxx> Signed-off-by: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx> --- 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
