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

From: Geert Uytterhoeven
Date: Fri Jun 08 2018 - 04:57:17 EST

Hi Arnd, Alexei,

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
> 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...

> default m
> help
> This builds bpfilter kernel module with embedded user mode helper



Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds