Subject: Re: [patch] powerpc: build modules outside the kernel tree fails, if it was built using O=

From: Yuri Frolov <[email-masked]>
Date: Sat, 26 Sep 2009 16:45:51 +0400

Hello, here is a fixed version.

Compile and export arch/powerpc/lib/crtsavres.o in order to fix the
"arch/powerpc/lib/crtsavres.o not found" error when "O=" option
is employed for external module compilation.
crtsavres.o is a support file, containing save/restore code from gcc,
simplified down for powerpc architecture needs.
This file needs to be linked against every module and thus to be built
before any module.

Documentation/kbuild/kbuild.txt |    8 ++++++++
Makefile                        |    2 +-
arch/powerpc/Makefile           |    2 +-
scripts/Makefile.modpost        |   14 ++++++++++++--
4 files changed, 22 insertions(+), 4 deletions(-)

diff -urpN -X linux-2.6/Documentation/dontdiff linux-2.6/arch/powerpc/Makefile linux-2.6-powerpc-crtsavres/arch/powerpc/Makefile
--- linux-2.6/arch/powerpc/Makefile	2009-09-17 20:04:31.000000000 +0400
+++ linux-2.6-powerpc-crtsavres/arch/powerpc/Makefile	2009-09-26 13:35:32.000000000 +0400
@@ -93,7 +93,7 @@ else
 	KBUILD_CFLAGS += $(call cc-option,-mtune=power4)
 endif
 else
-LDFLAGS_MODULE	+= arch/powerpc/lib/crtsavres.o
+KBUILD_MODULE_LINK_SOURCE += arch/powerpc/lib/crtsavres.o
 endif
 
 ifeq ($(CONFIG_TUNE_CELL),y)
diff -urpN -X linux-2.6/Documentation/dontdiff linux-2.6/Documentation/kbuild/kbuild.txt linux-2.6-powerpc-crtsavres/Documentation/kbuild/kbuild.txt
--- linux-2.6/Documentation/kbuild/kbuild.txt	2009-09-17 20:04:30.000000000 +0400
+++ linux-2.6-powerpc-crtsavres/Documentation/kbuild/kbuild.txt	2009-09-26 16:03:50.000000000 +0400
@@ -132,3 +132,11 @@ For tags/TAGS/cscope targets, you can sp
 to be included in the databases, separated by blank space. E.g.:
 
     $ make ALLSOURCE_ARCHS="x86 mips arm" tags
+
+KBUILD_MODULE_LINK_SOURCE
+--------------------------------------------------
+Compile and export arch/powerpc/lib/crtsavres.o
+when "O=" option is employed for powerpc external module compilation.
+This file needs to be linked against every module and thus to be built
+before any module.
+
diff -urpN -X linux-2.6/Documentation/dontdiff linux-2.6/Makefile linux-2.6-powerpc-crtsavres/Makefile
--- linux-2.6/Makefile	2009-09-17 20:04:30.000000000 +0400
+++ linux-2.6-powerpc-crtsavres/Makefile	2009-09-26 14:23:27.000000000 +0400
@@ -354,7 +354,7 @@ KERNELVERSION = $(VERSION).$(PATCHLEVEL)
 export VERSION PATCHLEVEL SUBLEVEL KERNELRELEASE KERNELVERSION
 export ARCH SRCARCH CONFIG_SHELL HOSTCC HOSTCFLAGS CROSS_COMPILE AS LD CC
 export CPP AR NM STRIP OBJCOPY OBJDUMP MAKE AWK GENKSYMS PERL UTS_MACHINE
-export HOSTCXX HOSTCXXFLAGS LDFLAGS_MODULE CHECK CHECKFLAGS
+export HOSTCXX HOSTCXXFLAGS LDFLAGS_MODULE CHECK CHECKFLAGS KBUILD_MODULE_LINK_SOURCE
 
 export KBUILD_CPPFLAGS NOSTDINC_FLAGS LINUXINCLUDE OBJCOPYFLAGS LDFLAGS
 export KBUILD_CFLAGS CFLAGS_KERNEL CFLAGS_MODULE CFLAGS_GCOV
diff -urpN -X linux-2.6/Documentation/dontdiff linux-2.6/scripts/Makefile.modpost linux-2.6-powerpc-crtsavres/scripts/Makefile.modpost
--- linux-2.6/scripts/Makefile.modpost	2009-09-17 20:04:42.000000000 +0400
+++ linux-2.6-powerpc-crtsavres/scripts/Makefile.modpost	2009-09-26 14:34:28.000000000 +0400
@@ -122,14 +122,24 @@ quiet_cmd_cc_o_c = CC      $@
       cmd_cc_o_c = $(CC) $(c_flags) $(CFLAGS_MODULE)	\
 		   -c -o $@ $<
 
-$(modules:.ko=.mod.o): %.mod.o: %.mod.c FORCE
+quiet_cmd_as_o_S = AS $(quiet_modtag)  $@
+      cmd_as_o_S = $(CC) $(a_flags) $(AFLAGS_MODULE) -c -o $@ $<
+
+ifdef KBUILD_MODULE_LINK_SOURCE
+$(KBUILD_MODULE_LINK_SOURCE): %.o: %.S FORCE
+	$(Q)mkdir -p $(dir $@)
+	$(call if_changed_dep,as_o_S)
+endif
+
+$(modules:.ko=.mod.o): %.mod.o: %.mod.c $(KBUILD_MODULE_LINK_SOURCE) FORCE
 	$(call if_changed_dep,cc_o_c)
 
 targets += $(modules:.ko=.mod.o)
 
 # Step 6), final link of the modules
 quiet_cmd_ld_ko_o = LD [M]  $@
-      cmd_ld_ko_o = $(LD) -r $(LDFLAGS) $(LDFLAGS_MODULE) -o $@		\
+      cmd_ld_ko_o = $(LD) -r $(LDFLAGS) $(KBUILD_MODULE_LINK_SOURCE)	\
+			  $(LDFLAGS_MODULE) -o $@			\
 			  $(filter-out FORCE,$^)
 
 $(modules): %.ko :%.o %.mod.o FORCE

On 09/25/2009 11:45 PM, Sam Ravnborg wrote:
> On Thu, Sep 24, 2009 at 03:28:11PM +0400, Yuri Frolov wrote:
>> Hello,
>>
>> here is a corresponding bug: http://bugzilla.kernel.org/show_bug.cgi?id=11143
>> This patch should correctly export crtsavres.o in order to make O= option working.
>> Please, consider to apply.
> 
> Hi Yuri.
> 
> I like the way you do the extra link in Makefile.modpost.
> But you need to redo some parts as per comments below.
> 
>>
>> Fix linking modules against crtsavres.o
> 
> Please elaborate more on what this commit does.
> 
>> Previously we got
>>   CC      drivers/char/hw_random/rng-core.mod.o
>>   LD [M]  drivers/char/hw_random/rng-core.ko
>> /there/src/buildroot.git.ppc/build_powerpc_nofpu/staging_dir/usr/bin/powerpc-linux-uclibc-ld: arch/powerpc/lib/crtsavres.o: No such file: No such file or directory
> 
> Always good to include error messages.
> 
>> 	* Makefile (LDFLAGS_MODULE_PREREQ): New variable to hold prerequisite
>>           files for modules.
>> 	* arch/powerpc/Makefile: add crtsavres.o to LDFLAGS_MODULE_PREREQ.
>> 	* scripts/Makefile.modpost (cmd_as_o_S): Copy from Makefile.build.
>> 	  (cmd_ld_ko_o): Also link LDFLAGS_MODULE_PREREQ.
>> 	  Provide rule to build objects from assembler.
> But this GNUism can go - we do not use it in the kernel.
>  
>> Signed-off-by:  Bernhard Reutner-Fischer  <[email-masked]>
>> Signed-off by:  Yuri Frolov <[email-masked]>
>>
>> Makefile                 |    2 ++
>> arch/powerpc/Makefile    |    2 +-
>> scripts/Makefile.modpost |   12 ++++++++++--
>> 3 files changed, 13 insertions(+), 3 deletions(-)
>>
>> diff -urpN -X linux-2.6/Documentation/dontdiff linux-2.6/arch/powerpc/Makefile linux-2.6-powerpc-crtsavres/arch/powerpc/Makefile
>> --- linux-2.6/arch/powerpc/Makefile	2009-09-17 20:04:31.000000000 +0400
>> +++ linux-2.6-powerpc-crtsavres/arch/powerpc/Makefile	2009-09-23 22:08:03.000000000 +0400
>> @@ -93,7 +93,7 @@ else
>>  	KBUILD_CFLAGS += $(call cc-option,-mtune=power4)
>>  endif
>>  else
>> -LDFLAGS_MODULE	+= arch/powerpc/lib/crtsavres.o
>> +LDFLAGS_MODULE_PREREQ += arch/powerpc/lib/crtsavres.o
>>  endif
> 
> The naming sucks.
> How about:
> 
> KBUILD_MODULE_LINK_SOURCE
> 
> This would tell the reader that this is source to be linked on a module.
> 
> And this is an arch specific thing so no need to preset it in top-level
> Makefile.
> But it is mandatory to include a description in Documentation/kbuild/kbuild.txt
> 
> 
>> --- linux-2.6/scripts/Makefile.modpost	2009-09-17 20:04:42.000000000 +0400
>> +++ linux-2.6-powerpc-crtsavres/scripts/Makefile.modpost	2009-09-23 22:15:00.000000000 +0400
>> @@ -122,14 +122,22 @@ quiet_cmd_cc_o_c = CC      $@
>>        cmd_cc_o_c = $(CC) $(c_flags) $(CFLAGS_MODULE)	\
>>  		   -c -o $@ $<
>>  
>> -$(modules:.ko=.mod.o): %.mod.o: %.mod.c FORCE
>> +quiet_cmd_as_o_S = AS $(quiet_modtag)  $@
>> +cmd_as_o_S       = $(CC) $(a_flags) $(AFLAGS_MODULE) -c -o $@ $<
> 
> Align this so cmd_as_o_S is under each other - as we do for cmd_cc_o_c
> 
> 
>> +
>> +$(LDFLAGS_MODULE_PREREQ): %.o: %.S FORCE
>> +	$(Q)mkdir -p $(dir $@)
>> +	$(call if_changed_dep,as_o_S)
> Good catch with the mkdir - needed for O= builds.
> I think we shall wrap this in
> ifdef KBUILD_MODULE_LINK_SOURCE
> ...
> endif
> 
> So we do not have an empty rule when it is not defined.
> 
> Please fix up these things and resubmit.
> 
> Thanks,
> 	Sam