Re: [PATCH] [net-next, wrong] make BPFILTER_UMH depend on X86

From: Daniel Borkmann
Date: Fri Jun 08 2018 - 05:33:32 EST

Hi Geert,

On 06/08/2018 10:57 AM, Geert Uytterhoeven wrote:
> On Mon, May 28, 2018 at 5:31 PM, Arnd Bergmann <arnd@xxxxxxxx> wrote:
>> When build testing across architectures, I run into a build error on
>> all targets other than X86:
>> gcc-8.1.0-nolibc/arm-linux-gnueabi/bin/arm-linux-gnueabi-objdump: net/bpfilter/bpfilter_umh: File format not recognized
>> gcc-8.1.0-nolibc/arm-linux-gnueabi/bin/arm-linux-gnueabi-objcopy:net/bpfilter/bpfilter_umh.o: Invalid bfd target
>> The problem is that 'hostprogs' get built with 'gcc' rather than
>> '$(CROSS_COMPILE)gcc', and my default gcc (as most people's) targets x86.
>> To work around it, adding an X86 dependency gets randconfigs building
>> again on my box.
>> Clearly, this is not a good solution, since it should actually work fine
>> when building native kernels on other architectures but that is now
>> disabled, while cross building an x86 kernel on another host is still
>> broken after my patch.
>> What we probably want here is to try out if the compiler is able to build
>> executables for the target architecture and not build the helper otherwise,
>> at least when compile-testing. No idea how to do that though.
> So that was done in commit 819dd92b9c0bc7bc ("bpfilter: switch to CC
> from HOSTCC"), but it is not sufficient:
> GEN net/bpfilter/bpfilter_umh.o
> Usage: m68k-linux-gnu-objcopy [option(s)] in-file [out-file]
> Copies a binary file, possibly transforming it in the process
> The options are:
> [...]
> net/bpfilter/Makefile:29: recipe for target 'net/bpfilter/bpfilter_umh.o' failed
> make[5]: *** [net/bpfilter/bpfilter_umh.o] Error 1
>> --- a/net/bpfilter/Kconfig
>> +++ b/net/bpfilter/Kconfig
>> @@ -9,6 +9,7 @@ menuconfig BPFILTER
>> config BPFILTER_UMH
>> tristate "bpfilter kernel module with user mode helper"
>> + depends on X86 # actually depends on native builds
> No, (currently) it does depend on X86, due to its use of:
> with CONFIG_OUTPUT_FORMAT being defined on X86 only...

That hard dependency should have been fixed with the following patch in -net tree: