kbuild: allow making undefined symbols fatal for external modules
diff mbox

Message ID 20171002105004.32426-1-jonas.gorski@gmail.com
State New
Headers show

Commit Message

Jonas Gorski Oct. 2, 2017, 10:50 a.m. UTC
By passing appropriate values in KBUILD_EXTRA_SYMBOLS it is possible to
make modpost be able to resolve all symbols for external modules, even
between to other external modules.

Because of this, it might be desirable to make unresolved symbols an
error on external module builds as well, to catch missing exports there
as well.

So add a new flag KBUILD_MODPOST_ERROR which can be set to enable this
behaviour. It has no effect on non external module builds.

Signed-off-by: Jonas Gorski <jonas.gorski@gmail.com>
---
The main target is to allow distributions (like LEDE) that make use of
kernel backports and other out of tree drivers to be able to catch
errors like missing EXPORT_SYMBOLs in the kernel early.

 scripts/Makefile.modpost | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

Comments

Masahiro Yamada Oct. 9, 2017, 4:25 p.m. UTC | #1
2017-10-02 19:50 GMT+09:00 Jonas Gorski <jonas.gorski@gmail.com>:
> By passing appropriate values in KBUILD_EXTRA_SYMBOLS it is possible to
> make modpost be able to resolve all symbols for external modules, even
> between to other external modules.
>
> Because of this, it might be desirable to make unresolved symbols an
> error on external module builds as well, to catch missing exports there
> as well.
>
> So add a new flag KBUILD_MODPOST_ERROR which can be set to enable this
> behaviour. It has no effect on non external module builds.
>
> Signed-off-by: Jonas Gorski <jonas.gorski@gmail.com>
> ---
> The main target is to allow distributions (like LEDE) that make use of
> kernel backports and other out of tree drivers to be able to catch
> errors like missing EXPORT_SYMBOLs in the kernel early.
>
>  scripts/Makefile.modpost | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost
> index 16923ba4b5b1..29f787bf8c3a 100644
> --- a/scripts/Makefile.modpost
> +++ b/scripts/Makefile.modpost
> @@ -34,6 +34,8 @@
>
>  # KBUILD_MODPOST_WARN can be set to avoid error out in case of undefined
>  # symbols in the final module linking stage
> +# KBUILD_MODPOST_ERROR can be set to error out in case of undefined
> +# symbols in the final module linking stage for external modules
>  # KBUILD_MODPOST_NOFINAL can be set to skip the final link of modules.
>  # This is solely useful to speed up test compiles
>  PHONY := _modpost
> @@ -49,6 +51,8 @@ ifneq ($(KBUILD_EXTMOD),)
>  obj := $(KBUILD_EXTMOD)
>  src := $(obj)
>
> +KBUILD_MODPOST_WARN = $(if $(KBUILD_MODPOST_ERROR),,1)
> +
>  # Include the module's Makefile to find KBUILD_EXTRA_SYMBOLS
>  include $(if $(wildcard $(KBUILD_EXTMOD)/Kbuild), \
>               $(KBUILD_EXTMOD)/Kbuild, $(KBUILD_EXTMOD)/Makefile)
> @@ -78,7 +82,7 @@ modpost = scripts/mod/modpost                    \
>   $(if $(KBUILD_EXTMOD),-o $(modulesymfile))      \
>   $(if $(CONFIG_DEBUG_SECTION_MISMATCH),,-S)      \
>   $(if $(CONFIG_SECTION_MISMATCH_WARN_ONLY),,-E)  \
> - $(if $(KBUILD_EXTMOD)$(KBUILD_MODPOST_WARN),-w)
> + $(if $(KBUILD_MODPOST_WARN),-w)
>
>  MODPOST_OPT=$(subst -i,-n,$(filter -i,$(MAKEFLAGS)))
>


The motivation looks reasonable to me,
but having both KBUILD_MODPOST_WARN and KBUILD_MODPOST_ERROR
is a bit confusing, I think.

(Some people may wonder what would happen if both are set...)


So, here is my suggestion.


We have only KBUILD_MODPOST_WARN.

The default value is 1 for external module building.
                     0 for kernel building.


If you want to change the default behavior,
you can specify KBUILD_MODPOST_WARN=1 when building kernel,
or KBUILD_MODPOST_WARN=0 when building external module
from the command line.


Also, you need to update Documentation/kbuild/kbuild.txt
Jonas Gorski Oct. 10, 2017, 9:04 a.m. UTC | #2
Hi Masahiro,

On 9 October 2017 at 18:25, Masahiro Yamada
<yamada.masahiro@socionext.com> wrote:
> 2017-10-02 19:50 GMT+09:00 Jonas Gorski <jonas.gorski@gmail.com>:
>> By passing appropriate values in KBUILD_EXTRA_SYMBOLS it is possible to
>> make modpost be able to resolve all symbols for external modules, even
>> between to other external modules.
>>
>> Because of this, it might be desirable to make unresolved symbols an
>> error on external module builds as well, to catch missing exports there
>> as well.
>>
>> So add a new flag KBUILD_MODPOST_ERROR which can be set to enable this
>> behaviour. It has no effect on non external module builds.
>>
>> Signed-off-by: Jonas Gorski <jonas.gorski@gmail.com>
>> ---
>> The main target is to allow distributions (like LEDE) that make use of
>> kernel backports and other out of tree drivers to be able to catch
>> errors like missing EXPORT_SYMBOLs in the kernel early.
>>
>>  scripts/Makefile.modpost | 6 +++++-
>>  1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost
>> index 16923ba4b5b1..29f787bf8c3a 100644
>> --- a/scripts/Makefile.modpost
>> +++ b/scripts/Makefile.modpost
>> @@ -34,6 +34,8 @@
>>
>>  # KBUILD_MODPOST_WARN can be set to avoid error out in case of undefined
>>  # symbols in the final module linking stage
>> +# KBUILD_MODPOST_ERROR can be set to error out in case of undefined
>> +# symbols in the final module linking stage for external modules
>>  # KBUILD_MODPOST_NOFINAL can be set to skip the final link of modules.
>>  # This is solely useful to speed up test compiles
>>  PHONY := _modpost
>> @@ -49,6 +51,8 @@ ifneq ($(KBUILD_EXTMOD),)
>>  obj := $(KBUILD_EXTMOD)
>>  src := $(obj)
>>
>> +KBUILD_MODPOST_WARN = $(if $(KBUILD_MODPOST_ERROR),,1)
>> +
>>  # Include the module's Makefile to find KBUILD_EXTRA_SYMBOLS
>>  include $(if $(wildcard $(KBUILD_EXTMOD)/Kbuild), \
>>               $(KBUILD_EXTMOD)/Kbuild, $(KBUILD_EXTMOD)/Makefile)
>> @@ -78,7 +82,7 @@ modpost = scripts/mod/modpost                    \
>>   $(if $(KBUILD_EXTMOD),-o $(modulesymfile))      \
>>   $(if $(CONFIG_DEBUG_SECTION_MISMATCH),,-S)      \
>>   $(if $(CONFIG_SECTION_MISMATCH_WARN_ONLY),,-E)  \
>> - $(if $(KBUILD_EXTMOD)$(KBUILD_MODPOST_WARN),-w)
>> + $(if $(KBUILD_MODPOST_WARN),-w)
>>
>>  MODPOST_OPT=$(subst -i,-n,$(filter -i,$(MAKEFLAGS)))
>>
>
>
> The motivation looks reasonable to me,
> but having both KBUILD_MODPOST_WARN and KBUILD_MODPOST_ERROR
> is a bit confusing, I think.
>
> (Some people may wonder what would happen if both are set...)
>
>
> So, here is my suggestion.
>
>
> We have only KBUILD_MODPOST_WARN.
>
> The default value is 1 for external module building.
>                      0 for kernel building.
>
>
> If you want to change the default behavior,
> you can specify KBUILD_MODPOST_WARN=1 when building kernel,
> or KBUILD_MODPOST_WARN=0 when building external module
> from the command line.

Makes sense, I was thinking too complicated.

>
> Also, you need to update Documentation/kbuild/kbuild.txt

Indeed, I missed that. Will fix in v2.


Regards
Jonas
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Patch
diff mbox

diff --git a/scripts/Makefile.modpost b/scripts/Makefile.modpost
index 16923ba4b5b1..29f787bf8c3a 100644
--- a/scripts/Makefile.modpost
+++ b/scripts/Makefile.modpost
@@ -34,6 +34,8 @@ 
 
 # KBUILD_MODPOST_WARN can be set to avoid error out in case of undefined
 # symbols in the final module linking stage
+# KBUILD_MODPOST_ERROR can be set to error out in case of undefined
+# symbols in the final module linking stage for external modules
 # KBUILD_MODPOST_NOFINAL can be set to skip the final link of modules.
 # This is solely useful to speed up test compiles
 PHONY := _modpost
@@ -49,6 +51,8 @@  ifneq ($(KBUILD_EXTMOD),)
 obj := $(KBUILD_EXTMOD)
 src := $(obj)
 
+KBUILD_MODPOST_WARN = $(if $(KBUILD_MODPOST_ERROR),,1)
+
 # Include the module's Makefile to find KBUILD_EXTRA_SYMBOLS
 include $(if $(wildcard $(KBUILD_EXTMOD)/Kbuild), \
              $(KBUILD_EXTMOD)/Kbuild, $(KBUILD_EXTMOD)/Makefile)
@@ -78,7 +82,7 @@  modpost = scripts/mod/modpost                    \
  $(if $(KBUILD_EXTMOD),-o $(modulesymfile))      \
  $(if $(CONFIG_DEBUG_SECTION_MISMATCH),,-S)      \
  $(if $(CONFIG_SECTION_MISMATCH_WARN_ONLY),,-E)  \
- $(if $(KBUILD_EXTMOD)$(KBUILD_MODPOST_WARN),-w)
+ $(if $(KBUILD_MODPOST_WARN),-w)
 
 MODPOST_OPT=$(subst -i,-n,$(filter -i,$(MAKEFLAGS)))