kbuild: Include external modules compile flags
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Message ID 1580161806-8037-1-git-send-email-gvrose8192@gmail.com
State New
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Series
  • kbuild: Include external modules compile flags
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Commit Message

Gregory Rose Jan. 27, 2020, 9:50 p.m. UTC
Since this commit:
'commit 9b9a3f20cbe0 ("kbuild: split final module linking out into Makefile.modfinal")'
at least one out-of-tree external kernel module build fails
during the modfinal make phase because Makefile.modfinal does
not include the ccflags-y variable from the exernal module's Kbuild.
Make sure to include the external kernel module's Kbuild so that the
necessary command line flags from the external module are set.

Reported-by: David Ahern <dsahern@gmail.com>
CC: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Greg Rose <gvrose8192@gmail.com>
---
 scripts/Makefile.modfinal | 4 ++++
 1 file changed, 4 insertions(+)

Comments

Masahiro Yamada Jan. 28, 2020, 3:35 a.m. UTC | #1
On Tue, Jan 28, 2020 at 6:50 AM Greg Rose <gvrose8192@gmail.com> wrote:
>
> Since this commit:
> 'commit 9b9a3f20cbe0 ("kbuild: split final module linking out into Makefile.modfinal")'
> at least one out-of-tree external kernel module build fails
> during the modfinal make phase because Makefile.modfinal does
> not include the ccflags-y variable from the exernal module's Kbuild.

ccflags-y is passed only for compiling C files in that directory.

It is not used for compiling *.mod.c
This is true for both in-kernel and external modules.

So, ccflags-y is not a good choice
for passing such flags that should be globally effective.


Maybe, KCFLAGS should work.


module:
       $(MAKE) KCFLAGS=...  M=$(PWD) -C /lib/modules/$(uname -r)/build modules



> Make sure to include the external kernel module's Kbuild so that the
> necessary command line flags from the external module are set.
>
> Reported-by: David Ahern <dsahern@gmail.com>
> CC: Masahiro Yamada <yamada.masahiro@socionext.com>
> Signed-off-by: Greg Rose <gvrose8192@gmail.com>
> ---
>  scripts/Makefile.modfinal | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/scripts/Makefile.modfinal b/scripts/Makefile.modfinal
> index 411c1e60..a645ba6 100644
> --- a/scripts/Makefile.modfinal
> +++ b/scripts/Makefile.modfinal
> @@ -21,6 +21,10 @@ __modfinal: $(modules)
>  modname = $(notdir $(@:.mod.o=))
>  part-of-module = y
>
> +# Include the module's Makefile to find KBUILD_EXTRA_SYMBOLS
> +include $(if $(wildcard $(KBUILD_EXTMOD)/Kbuild), \
> +             $(KBUILD_EXTMOD)/Kbuild)
> +
>  quiet_cmd_cc_o_c = CC [M]  $@
>        cmd_cc_o_c = $(CC) $(c_flags) -c -o $@ $<
>
> --
> 1.8.3.1
>
Gregory Rose Jan. 28, 2020, 3:37 p.m. UTC | #2
On 1/27/2020 7:35 PM, Masahiro Yamada wrote:
> On Tue, Jan 28, 2020 at 6:50 AM Greg Rose <gvrose8192@gmail.com> wrote:
>> Since this commit:
>> 'commit 9b9a3f20cbe0 ("kbuild: split final module linking out into Makefile.modfinal")'
>> at least one out-of-tree external kernel module build fails
>> during the modfinal make phase because Makefile.modfinal does
>> not include the ccflags-y variable from the exernal module's Kbuild.
> ccflags-y is passed only for compiling C files in that directory.
>
> It is not used for compiling *.mod.c
> This is true for both in-kernel and external modules.
>
> So, ccflags-y is not a good choice
> for passing such flags that should be globally effective.
>
>
> Maybe, KCFLAGS should work.
>
>
> module:
>         $(MAKE) KCFLAGS=...  M=$(PWD) -C /lib/modules/$(uname -r)/build modules
>

Thanks,

I'll see if I can get that to work.

- Greg


>
>> Make sure to include the external kernel module's Kbuild so that the
>> necessary command line flags from the external module are set.
>>
>> Reported-by: David Ahern <dsahern@gmail.com>
>> CC: Masahiro Yamada <yamada.masahiro@socionext.com>
>> Signed-off-by: Greg Rose <gvrose8192@gmail.com>
>> ---
>>   scripts/Makefile.modfinal | 4 ++++
>>   1 file changed, 4 insertions(+)
>>
>> diff --git a/scripts/Makefile.modfinal b/scripts/Makefile.modfinal
>> index 411c1e60..a645ba6 100644
>> --- a/scripts/Makefile.modfinal
>> +++ b/scripts/Makefile.modfinal
>> @@ -21,6 +21,10 @@ __modfinal: $(modules)
>>   modname = $(notdir $(@:.mod.o=))
>>   part-of-module = y
>>
>> +# Include the module's Makefile to find KBUILD_EXTRA_SYMBOLS
>> +include $(if $(wildcard $(KBUILD_EXTMOD)/Kbuild), \
>> +             $(KBUILD_EXTMOD)/Kbuild)
>> +
>>   quiet_cmd_cc_o_c = CC [M]  $@
>>         cmd_cc_o_c = $(CC) $(c_flags) -c -o $@ $<
>>
>> --
>> 1.8.3.1
>>
>
Gregory Rose Jan. 29, 2020, 6:09 p.m. UTC | #3
On 1/28/2020 7:37 AM, Gregory Rose wrote:
> On 1/27/2020 7:35 PM, Masahiro Yamada wrote:
>> On Tue, Jan 28, 2020 at 6:50 AM Greg Rose <gvrose8192@gmail.com> wrote:
>>> Since this commit:
>>> 'commit 9b9a3f20cbe0 ("kbuild: split final module linking out into 
>>> Makefile.modfinal")'
>>> at least one out-of-tree external kernel module build fails
>>> during the modfinal make phase because Makefile.modfinal does
>>> not include the ccflags-y variable from the exernal module's Kbuild.
>> ccflags-y is passed only for compiling C files in that directory.
>>
>> It is not used for compiling *.mod.c
>> This is true for both in-kernel and external modules.
>>
>> So, ccflags-y is not a good choice
>> for passing such flags that should be globally effective.
>>
>>
>> Maybe, KCFLAGS should work.
>>
>>
>> module:
>>         $(MAKE) KCFLAGS=...  M=$(PWD) -C /lib/modules/$(uname 
>> -r)/build modules
>>

Hi Masahiro,

I'm unable to get that to work.  KCFLAGS does not seem to be used in 
Makefile.modfinal.

[snip]
>>> --- a/scripts/Makefile.modfinal
>>> +++ b/scripts/Makefile.modfinal
>>> @@ -21,6 +21,10 @@ __modfinal: $(modules)
>>>   modname = $(notdir $(@:.mod.o=))
>>>   part-of-module = y
>>>
>>> +# Include the module's Makefile to find KBUILD_EXTRA_SYMBOLS
>>> +include $(if $(wildcard $(KBUILD_EXTMOD)/Kbuild), \
>>> +             $(KBUILD_EXTMOD)/Kbuild)
>>> +

I continue to wonder why this it is so bad to include the external 
module's Kbuild.
It used to be included in Makefile.modpost and did no harm, and in fact 
was what
made our external build work at all in the past.  Without the ability to 
define our
local kernel module build environment during the modfinal make I see no 
way forward.

That said, I'm no expert on the Linux kernel Makefile 
interdependencies.  If you
have some other idea we could try I'm game.

Thanks,

- Greg
Masahiro Yamada Feb. 2, 2020, 6:07 a.m. UTC | #4
On Thu, Jan 30, 2020 at 3:09 AM Gregory Rose <gvrose8192@gmail.com> wrote:
>
>
> On 1/28/2020 7:37 AM, Gregory Rose wrote:
> > On 1/27/2020 7:35 PM, Masahiro Yamada wrote:
> >> On Tue, Jan 28, 2020 at 6:50 AM Greg Rose <gvrose8192@gmail.com> wrote:
> >>> Since this commit:
> >>> 'commit 9b9a3f20cbe0 ("kbuild: split final module linking out into
> >>> Makefile.modfinal")'
> >>> at least one out-of-tree external kernel module build fails
> >>> during the modfinal make phase because Makefile.modfinal does
> >>> not include the ccflags-y variable from the exernal module's Kbuild.
> >> ccflags-y is passed only for compiling C files in that directory.
> >>
> >> It is not used for compiling *.mod.c
> >> This is true for both in-kernel and external modules.
> >>
> >> So, ccflags-y is not a good choice
> >> for passing such flags that should be globally effective.
> >>
> >>
> >> Maybe, KCFLAGS should work.
> >>
> >>
> >> module:
> >>         $(MAKE) KCFLAGS=...  M=$(PWD) -C /lib/modules/$(uname
> >> -r)/build modules
> >>
>
> Hi Masahiro,
>
> I'm unable to get that to work.  KCFLAGS does not seem to be used in
> Makefile.modfinal.


I quickly tested it, and confirmed
KCFLAGS works for external modules, too.


Makefile.modfinal includes scripts/Makefile.lib


So,  c_flags contains $(KCFLAGS)

 c_flags -> KBUILD_CFLAGS -> KCFLAGS






> [snip]
> >>> --- a/scripts/Makefile.modfinal
> >>> +++ b/scripts/Makefile.modfinal
> >>> @@ -21,6 +21,10 @@ __modfinal: $(modules)
> >>>   modname = $(notdir $(@:.mod.o=))
> >>>   part-of-module = y
> >>>
> >>> +# Include the module's Makefile to find KBUILD_EXTRA_SYMBOLS
> >>> +include $(if $(wildcard $(KBUILD_EXTMOD)/Kbuild), \
> >>> +             $(KBUILD_EXTMOD)/Kbuild)
> >>> +
>
> I continue to wonder why this it is so bad to include the external
> module's Kbuild.


Because it is not correct behavior.


> It used to be included in Makefile.modpost and did no harm, and in fact
> was what
> made our external build work at all in the past.  Without the ability to
> define our
> local kernel module build environment during the modfinal make I see no
> way forward.


As I said, ccflags-y is not intended to be
passed to *.mod.c
Upstream modules never rely on it.

External module should not rely on it either.


>
> That said, I'm no expert on the Linux kernel Makefile
> interdependencies.  If you
> have some other idea we could try I'm game.
Gregory Rose Feb. 4, 2020, 10:02 p.m. UTC | #5
On 2/1/2020 10:07 PM, Masahiro Yamada wrote:
> On Thu, Jan 30, 2020 at 3:09 AM Gregory Rose <gvrose8192@gmail.com> wrote:
>>
>> On 1/28/2020 7:37 AM, Gregory Rose wrote:
>>> On 1/27/2020 7:35 PM, Masahiro Yamada wrote:
>>>> On Tue, Jan 28, 2020 at 6:50 AM Greg Rose <gvrose8192@gmail.com> wrote:
>>>>> Since this commit:
>>>>> 'commit 9b9a3f20cbe0 ("kbuild: split final module linking out into
>>>>> Makefile.modfinal")'
>>>>> at least one out-of-tree external kernel module build fails
>>>>> during the modfinal make phase because Makefile.modfinal does
>>>>> not include the ccflags-y variable from the exernal module's Kbuild.
>>>> ccflags-y is passed only for compiling C files in that directory.
>>>>
>>>> It is not used for compiling *.mod.c
>>>> This is true for both in-kernel and external modules.
>>>>
>>>> So, ccflags-y is not a good choice
>>>> for passing such flags that should be globally effective.
>>>>
>>>>
>>>> Maybe, KCFLAGS should work.
>>>>
>>>>
>>>> module:
>>>>          $(MAKE) KCFLAGS=...  M=$(PWD) -C /lib/modules/$(uname
>>>> -r)/build modules
>>>>
>> Hi Masahiro,
>>
>> I'm unable to get that to work.  KCFLAGS does not seem to be used in
>> Makefile.modfinal.
>
> I quickly tested it, and confirmed
> KCFLAGS works for external modules, too.
>
>
> Makefile.modfinal includes scripts/Makefile.lib
>
>
> So,  c_flags contains $(KCFLAGS)
>
>   c_flags -> KBUILD_CFLAGS -> KCFLAGS
>

Hi Masahiro,

I must have missed  something then - again, my unfamiliarity with the 
Linux Makefiles is probably tripping me up.  I'll
dig around and see if I can get that working.

Thanks for your help,

- Greg
Gregory Rose Feb. 5, 2020, 10:48 p.m. UTC | #6
On 2/1/2020 10:07 PM, Masahiro Yamada wrote:
> On Thu, Jan 30, 2020 at 3:09 AM Gregory Rose <gvrose8192@gmail.com> wrote:
>>
>> On 1/28/2020 7:37 AM, Gregory Rose wrote:
>>> On 1/27/2020 7:35 PM, Masahiro Yamada wrote:
>>>> On Tue, Jan 28, 2020 at 6:50 AM Greg Rose <gvrose8192@gmail.com> wrote:
>>>>> Since this commit:
>>>>> 'commit 9b9a3f20cbe0 ("kbuild: split final module linking out into
>>>>> Makefile.modfinal")'
>>>>> at least one out-of-tree external kernel module build fails
>>>>> during the modfinal make phase because Makefile.modfinal does
>>>>> not include the ccflags-y variable from the exernal module's Kbuild.
>>>> ccflags-y is passed only for compiling C files in that directory.
>>>>
>>>> It is not used for compiling *.mod.c
>>>> This is true for both in-kernel and external modules.
>>>>
>>>> So, ccflags-y is not a good choice
>>>> for passing such flags that should be globally effective.
>>>>
>>>>
>>>> Maybe, KCFLAGS should work.
>>>>
>>>>
>>>> module:
>>>>          $(MAKE) KCFLAGS=...  M=$(PWD) -C /lib/modules/$(uname
>>>> -r)/build modules
>>>>
>> Hi Masahiro,
>>
>> I'm unable to get that to work.  KCFLAGS does not seem to be used in
>> Makefile.modfinal.
>
> I quickly tested it, and confirmed
> KCFLAGS works for external modules, too.
>
>
> Makefile.modfinal includes scripts/Makefile.lib
>
>
> So,  c_flags contains $(KCFLAGS)
>
>   c_flags -> KBUILD_CFLAGS -> KCFLAGS
>
>
Hi Masahiro,

I found a way to make this work on the openvswitch out of tree kernel 
module.  KCFLAGS
doesn't work because it is added at the end of the gcc command line and 
we need to
add a '-include <file>' directive so that the include file comes 
*before* all other include
files.  I fix this by inserting the '-include <file>' command line 
option to the beginning
of our own Kbuild NOSTDINC variable.

Thanks for your help in debugging this.

- Greg

Patch
diff mbox series

diff --git a/scripts/Makefile.modfinal b/scripts/Makefile.modfinal
index 411c1e60..a645ba6 100644
--- a/scripts/Makefile.modfinal
+++ b/scripts/Makefile.modfinal
@@ -21,6 +21,10 @@  __modfinal: $(modules)
 modname = $(notdir $(@:.mod.o=))
 part-of-module = y
 
+# Include the module's Makefile to find KBUILD_EXTRA_SYMBOLS
+include $(if $(wildcard $(KBUILD_EXTMOD)/Kbuild), \
+             $(KBUILD_EXTMOD)/Kbuild)
+
 quiet_cmd_cc_o_c = CC [M]  $@
       cmd_cc_o_c = $(CC) $(c_flags) -c -o $@ $<