diff mbox series

[v2,2/2] kbuild: warn objects shared among multiple modules

Message ID 20221118191551.66448-2-masahiroy@kernel.org
State New
Headers
Series [v2,1/2] kbuild: add kbuild-file macro |

Commit Message

Masahiro Yamada Nov. 18, 2022, 7:15 p.m. UTC 
  If an object is shared among multiple modules, amd some of them are
configured as 'm', but the others as 'y', the shared object is built
as modular, then linked to the modules and vmlinux. This is a potential
issue because the expected CFLAGS are different between modules and
builtins.

Commit 637a642f5ca5 ("zstd: Fixing mixed module-builtin objects")
reported that this could be even more fatal in some cases such as
Clang LTO.

That commit fixed lib/zlib/zstd_{compress,decompress}, but there are
still more instances of breakage.

This commit adds a W=1 warning for shared objects, so that the kbuild
test robot, which provides build tests with W=1, will avoid a new
breakage slipping in.

Quick compile tests on v6.1-rc4 detected the following:

scripts/Makefile.build:252: ./drivers/block/rnbd/Makefile: rnbd-common.o is added to multiple modules: rnbd-client rnbd-server
scripts/Makefile.build:252: ./drivers/crypto/marvell/octeontx2/Makefile: cn10k_cpt.o is added to multiple modules: rvu_cptpf rvu_cptvf
scripts/Makefile.build:252: ./drivers/crypto/marvell/octeontx2/Makefile: otx2_cptlf.o is added to multiple modules: rvu_cptpf rvu_cptvf
scripts/Makefile.build:252: ./drivers/crypto/marvell/octeontx2/Makefile: otx2_cpt_mbox_common.o is added to multiple modules: rvu_cptpf rvu_cptvf
scripts/Makefile.build:252: ./drivers/edac/Makefile: skx_common.o is added to multiple modules: i10nm_edac skx_edac
scripts/Makefile.build:252: ./drivers/gpu/drm/bridge/imx/Makefile: imx-ldb-helper.o is added to multiple modules: imx8qm-ldb imx8qxp-ldb
scripts/Makefile.build:252: ./drivers/mfd/Makefile: rsmu_core.o is added to multiple modules: rsmu-i2c rsmu-spi
scripts/Makefile.build:252: ./drivers/mtd/tests/Makefile: mtd_test.o is added to multiple modules: mtd_nandbiterrs mtd_oobtest mtd_pagetest mtd_readtest mtd_speedtest mtd_stresstest mtd_subpagetest mtd_torturetest
scripts/Makefile.build:252: ./drivers/net/dsa/ocelot/Makefile: felix.o is added to multiple modules: mscc_felix mscc_seville
scripts/Makefile.build:252: ./drivers/net/ethernet/cavium/liquidio/Makefile: cn23xx_pf_device.o is added to multiple modules: liquidio liquidio_vf
scripts/Makefile.build:252: ./drivers/net/ethernet/cavium/liquidio/Makefile: cn23xx_vf_device.o is added to multiple modules: liquidio liquidio_vf
scripts/Makefile.build:252: ./drivers/net/ethernet/cavium/liquidio/Makefile: cn66xx_device.o is added to multiple modules: liquidio liquidio_vf
scripts/Makefile.build:252: ./drivers/net/ethernet/cavium/liquidio/Makefile: cn68xx_device.o is added to multiple modules: liquidio liquidio_vf
scripts/Makefile.build:252: ./drivers/net/ethernet/cavium/liquidio/Makefile: lio_core.o is added to multiple modules: liquidio liquidio_vf
scripts/Makefile.build:252: ./drivers/net/ethernet/cavium/liquidio/Makefile: lio_ethtool.o is added to multiple modules: liquidio liquidio_vf
scripts/Makefile.build:252: ./drivers/net/ethernet/cavium/liquidio/Makefile: octeon_device.o is added to multiple modules: liquidio liquidio_vf
scripts/Makefile.build:252: ./drivers/net/ethernet/cavium/liquidio/Makefile: octeon_droq.o is added to multiple modules: liquidio liquidio_vf
scripts/Makefile.build:252: ./drivers/net/ethernet/cavium/liquidio/Makefile: octeon_mailbox.o is added to multiple modules: liquidio liquidio_vf
scripts/Makefile.build:252: ./drivers/net/ethernet/cavium/liquidio/Makefile: octeon_mem_ops.o is added to multiple modules: liquidio liquidio_vf
scripts/Makefile.build:252: ./drivers/net/ethernet/cavium/liquidio/Makefile: octeon_nic.o is added to multiple modules: liquidio liquidio_vf
scripts/Makefile.build:252: ./drivers/net/ethernet/cavium/liquidio/Makefile: request_manager.o is added to multiple modules: liquidio liquidio_vf
scripts/Makefile.build:252: ./drivers/net/ethernet/cavium/liquidio/Makefile: response_manager.o is added to multiple modules: liquidio liquidio_vf
scripts/Makefile.build:252: ./drivers/net/ethernet/freescale/dpaa2/Makefile: dpaa2-mac.o is added to multiple modules: fsl-dpaa2-eth fsl-dpaa2-switch
scripts/Makefile.build:252: ./drivers/net/ethernet/freescale/dpaa2/Makefile: dpmac.o is added to multiple modules: fsl-dpaa2-eth fsl-dpaa2-switch
scripts/Makefile.build:252: ./drivers/net/ethernet/freescale/enetc/Makefile: enetc_cbdr.o is added to multiple modules: fsl-enetc fsl-enetc-vf
scripts/Makefile.build:252: ./drivers/net/ethernet/freescale/enetc/Makefile: enetc_ethtool.o is added to multiple modules: fsl-enetc fsl-enetc-vf
scripts/Makefile.build:252: ./drivers/net/ethernet/freescale/enetc/Makefile: enetc.o is added to multiple modules: fsl-enetc fsl-enetc-vf
scripts/Makefile.build:252: ./drivers/net/ethernet/hisilicon/hns3/Makefile: hns3_common/hclge_comm_cmd.o is added to multiple modules: hclge hclgevf
scripts/Makefile.build:252: ./drivers/net/ethernet/hisilicon/hns3/Makefile: hns3_common/hclge_comm_rss.o is added to multiple modules: hclge hclgevf
scripts/Makefile.build:252: ./drivers/net/ethernet/hisilicon/hns3/Makefile: hns3_common/hclge_comm_tqp_stats.o is added to multiple modules: hclge hclgevf
scripts/Makefile.build:252: ./drivers/net/ethernet/marvell/octeontx2/nic/Makefile: otx2_dcbnl.o is added to multiple modules: rvu_nicpf rvu_nicvf
scripts/Makefile.build:252: ./drivers/net/ethernet/marvell/octeontx2/nic/Makefile: otx2_devlink.o is added to multiple modules: rvu_nicpf rvu_nicvf
scripts/Makefile.build:252: ./drivers/net/ethernet/ti/Makefile: cpsw_ale.o is added to multiple modules: keystone_netcp keystone_netcp_ethss ti_cpsw ti_cpsw_new
scripts/Makefile.build:252: ./drivers/net/ethernet/ti/Makefile: cpsw_ethtool.o is added to multiple modules: ti_cpsw ti_cpsw_new
scripts/Makefile.build:252: ./drivers/net/ethernet/ti/Makefile: cpsw_priv.o is added to multiple modules: ti_cpsw ti_cpsw_new
scripts/Makefile.build:252: ./drivers/net/ethernet/ti/Makefile: cpsw_sl.o is added to multiple modules: ti_cpsw ti_cpsw_new
scripts/Makefile.build:252: ./drivers/net/ethernet/ti/Makefile: davinci_cpdma.o is added to multiple modules: ti_cpsw ti_cpsw_new ti_davinci_emac
scripts/Makefile.build:252: ./drivers/platform/x86/intel/int3472/Makefile: common.o is added to multiple modules: intel_skl_int3472_discrete intel_skl_int3472_tps68470
scripts/Makefile.build:252: ./sound/soc/codecs/Makefile: wcd-clsh-v2.o is added to multiple modules: snd-soc-wcd9335 snd-soc-wcd934x snd-soc-wcd938x

Once all the warnings are fixed, it can become an error irrespective of
W= option.

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

Changes in v2:
  - Add drivers/block/rnbd/Makefile for commit log

 scripts/Makefile.build | 6 ++++++
 1 file changed, 6 insertions(+)

Comments

Alexander Lobakin Nov. 18, 2022, 9:35 p.m. UTC | #1 
From: Masahiro Yamada <masahiroy@kernel.org>
Date: Sat, 19 Nov 2022 04:15:51 +0900

> If an object is shared among multiple modules, amd some of them are
> configured as 'm', but the others as 'y', the shared object is built
> as modular, then linked to the modules and vmlinux. This is a potential
> issue because the expected CFLAGS are different between modules and
> builtins.
>
> Commit 637a642f5ca5 ("zstd: Fixing mixed module-builtin objects")
> reported that this could be even more fatal in some cases such as
> Clang LTO.
>
> That commit fixed lib/zlib/zstd_{compress,decompress}, but there are
> still more instances of breakage.
>
> This commit adds a W=1 warning for shared objects, so that the kbuild
> test robot, which provides build tests with W=1, will avoid a new
> breakage slipping in.
>
> Quick compile tests on v6.1-rc4 detected the following:

For the series:

Reviewed-and-tested-by: Alexander Lobakin <alobakin@pm.me>

[...]

> Once all the warnings are fixed, it can become an error irrespective of
> W= option.

BTW I've fixed most of these (the ones that get build on typical
x86_64 distroconfig) during my local tests, basing off your WIP
tree. I could send a series if you wish.

>
> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> ---
>
> Changes in v2:
>   - Add drivers/block/rnbd/Makefile for commit log
>
>  scripts/Makefile.build | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> index 37cf88d076e8..799df12b53f3 100644
> --- a/scripts/Makefile.build
> +++ b/scripts/Makefile.build
> @@ -222,6 +222,10 @@ endif
>
>  cmd_check_local_export = $(srctree)/scripts/check-local-export $@
>
> +ifneq ($(findstring 1, $(KBUILD_EXTRA_WARN)),)
> +cmd_warn_shared_object = $(if $(word 2, $(modname-multi)),$(warning $(kbuild-file): $*.o is added to multiple modules: $(modname-multi)))
> +endif
> +
>  define rule_cc_o_c
>  	$(call cmd_and_fixdep,cc_o_c)
>  	$(call cmd,gen_ksymdeps)
> @@ -231,6 +235,7 @@ define rule_cc_o_c
>  	$(call cmd,gen_objtooldep)
>  	$(call cmd,gen_symversions_c)
>  	$(call cmd,record_mcount)
> +	$(call cmd,warn_shared_object)
>  endef
>
>  define rule_as_o_S
> @@ -239,6 +244,7 @@ define rule_as_o_S
>  	$(call cmd,check_local_export)
>  	$(call cmd,gen_objtooldep)
>  	$(call cmd,gen_symversions_S)
> +	$(call cmd,warn_shared_object)
>  endef
>
>  # Built-in and composite module parts
> --
> 2.34.1

Thanks,
Olek
Masahiro Yamada Nov. 19, 2022, 6:09 a.m. UTC | #2 
On Sat, Nov 19, 2022 at 6:36 AM Alexander Lobakin <alobakin@pm.me> wrote:
>
> From: Masahiro Yamada <masahiroy@kernel.org>
> Date: Sat, 19 Nov 2022 04:15:51 +0900
>
> > If an object is shared among multiple modules, amd some of them are
> > configured as 'm', but the others as 'y', the shared object is built
> > as modular, then linked to the modules and vmlinux. This is a potential
> > issue because the expected CFLAGS are different between modules and
> > builtins.
> >
> > Commit 637a642f5ca5 ("zstd: Fixing mixed module-builtin objects")
> > reported that this could be even more fatal in some cases such as
> > Clang LTO.
> >
> > That commit fixed lib/zlib/zstd_{compress,decompress}, but there are
> > still more instances of breakage.
> >
> > This commit adds a W=1 warning for shared objects, so that the kbuild
> > test robot, which provides build tests with W=1, will avoid a new
> > breakage slipping in.
> >
> > Quick compile tests on v6.1-rc4 detected the following:
>
> For the series:
>
> Reviewed-and-tested-by: Alexander Lobakin <alobakin@pm.me>
>
> [...]
>
> > Once all the warnings are fixed, it can become an error irrespective of
> > W= option.
>
> BTW I've fixed most of these (the ones that get build on typical
> x86_64 distroconfig) during my local tests, basing off your WIP
> tree. I could send a series if you wish.


Yes, thanks for the help.




>
> >
> > Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> > ---
> >
> > Changes in v2:
> >   - Add drivers/block/rnbd/Makefile for commit log
> >
> >  scripts/Makefile.build | 6 ++++++
> >  1 file changed, 6 insertions(+)
> >
> > diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> > index 37cf88d076e8..799df12b53f3 100644
> > --- a/scripts/Makefile.build
> > +++ b/scripts/Makefile.build
> > @@ -222,6 +222,10 @@ endif
> >
> >  cmd_check_local_export = $(srctree)/scripts/check-local-export $@
> >
> > +ifneq ($(findstring 1, $(KBUILD_EXTRA_WARN)),)
> > +cmd_warn_shared_object = $(if $(word 2, $(modname-multi)),$(warning $(kbuild-file): $*.o is added to multiple modules: $(modname-multi)))
> > +endif
> > +
> >  define rule_cc_o_c
> >       $(call cmd_and_fixdep,cc_o_c)
> >       $(call cmd,gen_ksymdeps)
> > @@ -231,6 +235,7 @@ define rule_cc_o_c
> >       $(call cmd,gen_objtooldep)
> >       $(call cmd,gen_symversions_c)
> >       $(call cmd,record_mcount)
> > +     $(call cmd,warn_shared_object)
> >  endef
> >
> >  define rule_as_o_S
> > @@ -239,6 +244,7 @@ define rule_as_o_S
> >       $(call cmd,check_local_export)
> >       $(call cmd,gen_objtooldep)
> >       $(call cmd,gen_symversions_S)
> > +     $(call cmd,warn_shared_object)
> >  endef
> >
> >  # Built-in and composite module parts
> > --
> > 2.34.1
>
> Thanks,
> Olek
>
Nicolas Schier Nov. 22, 2022, 6:20 a.m. UTC | #3 
On Sat 19 Nov 2022 04:15:51 GMT, Masahiro Yamada wrote:
> If an object is shared among multiple modules, amd some of them are

amd -> and

Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>

> configured as 'm', but the others as 'y', the shared object is built
> as modular, then linked to the modules and vmlinux. This is a potential
> issue because the expected CFLAGS are different between modules and
> builtins.
> 
> Commit 637a642f5ca5 ("zstd: Fixing mixed module-builtin objects")
> reported that this could be even more fatal in some cases such as
> Clang LTO.
> 
> That commit fixed lib/zlib/zstd_{compress,decompress}, but there are
> still more instances of breakage.
> 
> This commit adds a W=1 warning for shared objects, so that the kbuild
> test robot, which provides build tests with W=1, will avoid a new
> breakage slipping in.
> 
> Quick compile tests on v6.1-rc4 detected the following:
> 
> scripts/Makefile.build:252: ./drivers/block/rnbd/Makefile: rnbd-common.o is added to multiple modules: rnbd-client rnbd-server
> scripts/Makefile.build:252: ./drivers/crypto/marvell/octeontx2/Makefile: cn10k_cpt.o is added to multiple modules: rvu_cptpf rvu_cptvf
> scripts/Makefile.build:252: ./drivers/crypto/marvell/octeontx2/Makefile: otx2_cptlf.o is added to multiple modules: rvu_cptpf rvu_cptvf
> scripts/Makefile.build:252: ./drivers/crypto/marvell/octeontx2/Makefile: otx2_cpt_mbox_common.o is added to multiple modules: rvu_cptpf rvu_cptvf
> scripts/Makefile.build:252: ./drivers/edac/Makefile: skx_common.o is added to multiple modules: i10nm_edac skx_edac
> scripts/Makefile.build:252: ./drivers/gpu/drm/bridge/imx/Makefile: imx-ldb-helper.o is added to multiple modules: imx8qm-ldb imx8qxp-ldb
> scripts/Makefile.build:252: ./drivers/mfd/Makefile: rsmu_core.o is added to multiple modules: rsmu-i2c rsmu-spi
> scripts/Makefile.build:252: ./drivers/mtd/tests/Makefile: mtd_test.o is added to multiple modules: mtd_nandbiterrs mtd_oobtest mtd_pagetest mtd_readtest mtd_speedtest mtd_stresstest mtd_subpagetest mtd_torturetest
> scripts/Makefile.build:252: ./drivers/net/dsa/ocelot/Makefile: felix.o is added to multiple modules: mscc_felix mscc_seville
> scripts/Makefile.build:252: ./drivers/net/ethernet/cavium/liquidio/Makefile: cn23xx_pf_device.o is added to multiple modules: liquidio liquidio_vf
> scripts/Makefile.build:252: ./drivers/net/ethernet/cavium/liquidio/Makefile: cn23xx_vf_device.o is added to multiple modules: liquidio liquidio_vf
> scripts/Makefile.build:252: ./drivers/net/ethernet/cavium/liquidio/Makefile: cn66xx_device.o is added to multiple modules: liquidio liquidio_vf
> scripts/Makefile.build:252: ./drivers/net/ethernet/cavium/liquidio/Makefile: cn68xx_device.o is added to multiple modules: liquidio liquidio_vf
> scripts/Makefile.build:252: ./drivers/net/ethernet/cavium/liquidio/Makefile: lio_core.o is added to multiple modules: liquidio liquidio_vf
> scripts/Makefile.build:252: ./drivers/net/ethernet/cavium/liquidio/Makefile: lio_ethtool.o is added to multiple modules: liquidio liquidio_vf
> scripts/Makefile.build:252: ./drivers/net/ethernet/cavium/liquidio/Makefile: octeon_device.o is added to multiple modules: liquidio liquidio_vf
> scripts/Makefile.build:252: ./drivers/net/ethernet/cavium/liquidio/Makefile: octeon_droq.o is added to multiple modules: liquidio liquidio_vf
> scripts/Makefile.build:252: ./drivers/net/ethernet/cavium/liquidio/Makefile: octeon_mailbox.o is added to multiple modules: liquidio liquidio_vf
> scripts/Makefile.build:252: ./drivers/net/ethernet/cavium/liquidio/Makefile: octeon_mem_ops.o is added to multiple modules: liquidio liquidio_vf
> scripts/Makefile.build:252: ./drivers/net/ethernet/cavium/liquidio/Makefile: octeon_nic.o is added to multiple modules: liquidio liquidio_vf
> scripts/Makefile.build:252: ./drivers/net/ethernet/cavium/liquidio/Makefile: request_manager.o is added to multiple modules: liquidio liquidio_vf
> scripts/Makefile.build:252: ./drivers/net/ethernet/cavium/liquidio/Makefile: response_manager.o is added to multiple modules: liquidio liquidio_vf
> scripts/Makefile.build:252: ./drivers/net/ethernet/freescale/dpaa2/Makefile: dpaa2-mac.o is added to multiple modules: fsl-dpaa2-eth fsl-dpaa2-switch
> scripts/Makefile.build:252: ./drivers/net/ethernet/freescale/dpaa2/Makefile: dpmac.o is added to multiple modules: fsl-dpaa2-eth fsl-dpaa2-switch
> scripts/Makefile.build:252: ./drivers/net/ethernet/freescale/enetc/Makefile: enetc_cbdr.o is added to multiple modules: fsl-enetc fsl-enetc-vf
> scripts/Makefile.build:252: ./drivers/net/ethernet/freescale/enetc/Makefile: enetc_ethtool.o is added to multiple modules: fsl-enetc fsl-enetc-vf
> scripts/Makefile.build:252: ./drivers/net/ethernet/freescale/enetc/Makefile: enetc.o is added to multiple modules: fsl-enetc fsl-enetc-vf
> scripts/Makefile.build:252: ./drivers/net/ethernet/hisilicon/hns3/Makefile: hns3_common/hclge_comm_cmd.o is added to multiple modules: hclge hclgevf
> scripts/Makefile.build:252: ./drivers/net/ethernet/hisilicon/hns3/Makefile: hns3_common/hclge_comm_rss.o is added to multiple modules: hclge hclgevf
> scripts/Makefile.build:252: ./drivers/net/ethernet/hisilicon/hns3/Makefile: hns3_common/hclge_comm_tqp_stats.o is added to multiple modules: hclge hclgevf
> scripts/Makefile.build:252: ./drivers/net/ethernet/marvell/octeontx2/nic/Makefile: otx2_dcbnl.o is added to multiple modules: rvu_nicpf rvu_nicvf
> scripts/Makefile.build:252: ./drivers/net/ethernet/marvell/octeontx2/nic/Makefile: otx2_devlink.o is added to multiple modules: rvu_nicpf rvu_nicvf
> scripts/Makefile.build:252: ./drivers/net/ethernet/ti/Makefile: cpsw_ale.o is added to multiple modules: keystone_netcp keystone_netcp_ethss ti_cpsw ti_cpsw_new
> scripts/Makefile.build:252: ./drivers/net/ethernet/ti/Makefile: cpsw_ethtool.o is added to multiple modules: ti_cpsw ti_cpsw_new
> scripts/Makefile.build:252: ./drivers/net/ethernet/ti/Makefile: cpsw_priv.o is added to multiple modules: ti_cpsw ti_cpsw_new
> scripts/Makefile.build:252: ./drivers/net/ethernet/ti/Makefile: cpsw_sl.o is added to multiple modules: ti_cpsw ti_cpsw_new
> scripts/Makefile.build:252: ./drivers/net/ethernet/ti/Makefile: davinci_cpdma.o is added to multiple modules: ti_cpsw ti_cpsw_new ti_davinci_emac
> scripts/Makefile.build:252: ./drivers/platform/x86/intel/int3472/Makefile: common.o is added to multiple modules: intel_skl_int3472_discrete intel_skl_int3472_tps68470
> scripts/Makefile.build:252: ./sound/soc/codecs/Makefile: wcd-clsh-v2.o is added to multiple modules: snd-soc-wcd9335 snd-soc-wcd934x snd-soc-wcd938x
> 
> Once all the warnings are fixed, it can become an error irrespective of
> W= option.
> 
> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
> ---
> 
> Changes in v2:
>   - Add drivers/block/rnbd/Makefile for commit log
> 
>  scripts/Makefile.build | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> index 37cf88d076e8..799df12b53f3 100644
> --- a/scripts/Makefile.build
> +++ b/scripts/Makefile.build
> @@ -222,6 +222,10 @@ endif
>  
>  cmd_check_local_export = $(srctree)/scripts/check-local-export $@
>  
> +ifneq ($(findstring 1, $(KBUILD_EXTRA_WARN)),)
> +cmd_warn_shared_object = $(if $(word 2, $(modname-multi)),$(warning $(kbuild-file): $*.o is added to multiple modules: $(modname-multi)))
> +endif
> +
>  define rule_cc_o_c
>  	$(call cmd_and_fixdep,cc_o_c)
>  	$(call cmd,gen_ksymdeps)
> @@ -231,6 +235,7 @@ define rule_cc_o_c
>  	$(call cmd,gen_objtooldep)
>  	$(call cmd,gen_symversions_c)
>  	$(call cmd,record_mcount)
> +	$(call cmd,warn_shared_object)
>  endef
>  
>  define rule_as_o_S
> @@ -239,6 +244,7 @@ define rule_as_o_S
>  	$(call cmd,check_local_export)
>  	$(call cmd,gen_objtooldep)
>  	$(call cmd,gen_symversions_S)
> +	$(call cmd,warn_shared_object)
>  endef
>  
>  # Built-in and composite module parts
> -- 
> 2.34.1
diff mbox series

Patch

diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 37cf88d076e8..799df12b53f3 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -222,6 +222,10 @@  endif
 
 cmd_check_local_export = $(srctree)/scripts/check-local-export $@
 
+ifneq ($(findstring 1, $(KBUILD_EXTRA_WARN)),)
+cmd_warn_shared_object = $(if $(word 2, $(modname-multi)),$(warning $(kbuild-file): $*.o is added to multiple modules: $(modname-multi)))
+endif
+
 define rule_cc_o_c
 	$(call cmd_and_fixdep,cc_o_c)
 	$(call cmd,gen_ksymdeps)
@@ -231,6 +235,7 @@  define rule_cc_o_c
 	$(call cmd,gen_objtooldep)
 	$(call cmd,gen_symversions_c)
 	$(call cmd,record_mcount)
+	$(call cmd,warn_shared_object)
 endef
 
 define rule_as_o_S
@@ -239,6 +244,7 @@  define rule_as_o_S
 	$(call cmd,check_local_export)
 	$(call cmd,gen_objtooldep)
 	$(call cmd,gen_symversions_S)
+	$(call cmd,warn_shared_object)
 endef
 
 # Built-in and composite module parts