umh build...

Alexei, I tried to build bpfilter on sparc64 and it shows that
CONFIG_OUTPUT_FORMAT is an x86 specific Kconfig value.

And, even if I added it, it's not clear what it should even be set to.

Right now, for example, my userland builds default to 32-bit sparc
even though I'm building a 64-bit kernel.

I think what ends up happening has to be in some way in response to
what kind of "native" binaries HOSTCC is actually building.

On Tue, Jun 05, 2018 at 05:03:59PM -0400, David Miller wrote:

Alexei, I tried to build bpfilter on sparc64 and it shows that
CONFIG_OUTPUT_FORMAT is an x86 specific Kconfig value.

And, even if I added it, it's not clear what it should even be set to.

Right now, for example, my userland builds default to 32-bit sparc
even though I'm building a 64-bit kernel.

I think what ends up happening has to be in some way in response to
what kind of "native" binaries HOSTCC is actually building.

I guess you mean native-ness not of HOSTCC, but what target rootfs will be.
I guess it's probably equal to 32 or 64-bitness of the kernel from CC.

I completely forgot that I need to fix CONFIG_OUTPUT_FORMAT.
On my arm64 I just did
export CONFIG_OUTPUT_FORMAT=elf64-littleaarch64
before doing 'make'.
I can do a hack to extract it from objdump
similar to the hack I do for '-B ...'
Like the patch below...
and it works on x64 too, but I'm not sure about sparc.

From e216123e54041f73ecf1676e355bc83e80c63d1d Mon Sep 17 00:00:00 2001

Date: Tue, 5 Jun 2018 15:27:07 -0700
Subject: [PATCH] bpfilter: fix OUTPUT_FORMAT

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
---
 net/bpfilter/Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/bpfilter/Makefile b/net/bpfilter/Makefile
index aafa72001fcd..e0bbe7583e58 100644
--- a/net/bpfilter/Makefile
+++ b/net/bpfilter/Makefile

@@ -21,7 +21,7 @@ endif
 # which bpfilter_kern.c passes further into umh blob loader at run-time
 quiet_cmd_copy_umh = GEN $@
       cmd_copy_umh = echo ':' > $(obj)/.bpfilter_umh.o.cmd; \
-      $(OBJCOPY) -I binary -O $(CONFIG_OUTPUT_FORMAT) \
+      $(OBJCOPY) -I binary -O `$(OBJDUMP) -f $<|grep format|cut -d' ' -f8` \
       -B `$(OBJDUMP) -f $<|grep architecture|cut -d, -f1|cut -d' ' -f2` \
       --rename-section .data=.init.rodata $< $@

From: Alexei Starovoitov <redacted>
Date: Tue, 5 Jun 2018 15:29:34 -0700

On Tue, Jun 05, 2018 at 05:03:59PM -0400, David Miller wrote:

quoted

Alexei, I tried to build bpfilter on sparc64 and it shows that
CONFIG_OUTPUT_FORMAT is an x86 specific Kconfig value.

And, even if I added it, it's not clear what it should even be set to.

Right now, for example, my userland builds default to 32-bit sparc
even though I'm building a 64-bit kernel.

I think what ends up happening has to be in some way in response to
what kind of "native" binaries HOSTCC is actually building.

I guess you mean native-ness not of HOSTCC, but what target rootfs will be.

Target rootfs is where I am building the kernel in this case.

Kernel running is 64-bit, most of userland is 32-bit.  Kernel is built
explicitly with "-m64" but gcc by default is building 32-bit.

I guess it's probably equal to 32 or 64-bitness of the kernel from
CC.

Nope, they are and can be different, even natively.

I completely forgot that I need to fix CONFIG_OUTPUT_FORMAT.
On my arm64 I just did
export CONFIG_OUTPUT_FORMAT=elf64-littleaarch64
before doing 'make'.
I can do a hack to extract it from objdump
similar to the hack I do for '-B ...'
Like the patch below...
and it works on x64 too, but I'm not sure about sparc.

 ...

Yeah this doesn't do it in the 64-bit kernel 32-bit userspace scenerio.

We build UMH which ends up being a 32-bit ELF binary, then we later
try to link it:

  ld -m elf64_sparc   -r -o net/bpfilter/bpfilter.o net/bpfilter/bpfilter_kern.o net/bpfilter/bpfilter_umh.o ; scripts/mod/modpost net/bpfilter/bpfilter.o
ld: sparc:v8plusb architecture of input file `net/bpfilter/bpfilter_umh.o' is incompatible with sparc:v9 output

But your patch is a step in the right direction because it gets us
away from depending upon CONFIG_OUTPUT_FORMAT.