Re: [GIT] Networking

Hi Matteo,

On Thu, 21 Jun 2018 13:40:43 +0000 Matteo Croce [off-list ref] wrote:

On Thu, Jun 21, 2018 at 8:46 AM Ingo Molnar [off-list ref] wrote:

quoted

* David Miller [off-list ref] wrote:
 

quoted

1) Fix crash on bpf_prog_load() errors, from Daniel Borkmann.  

quoted

Daniel Borkmann (4):
      Merge branch 'bpf-misc-fixes'
      bpf: fix panic in prog load calls cleanup
      bpf: reject any prog that failed read-only lock
      bpf, xdp, i40e: fix i40e_build_skb skb reserve and truesize  

JFYI, I'm still seeing this BPF build error upstream, on a 32-bit allyesconfig I'm
getting:

  LD      vmlinux.o
  ld: i386:x86-64 architecture of input file `net/bpfilter/bpfilter_umh.o' is incompatible with i386 output
  Makefile:1010: recipe for target 'vmlinux' failed
  make: *** [vmlinux] Error 1

A similar looking build bug was reported by sfr three weeks ago:
 

quoted

Subject: linux-next: build failure after merge of the net-next tree

...

x86_64-linux-ld: unknown architecture of input file `net/bpfilter/bpfilter_umh.o'
is incompatible with i386:x86-64 output

Caused by commit

 d2ba09c17a06 ("net: add skeleton of bpfilter kernel module")

In my builds, the host is PowerPC 64 LE ...

I have reverted that commit along with

 61a552eb487f ("bpfilter: fix build dependency")
 13405468f49d ("bpfilter: don't pass O_CREAT when opening console for debug")

for today.  

Is there a fix I could try?

are you compiling a 32 bit kernel on an x86_64 host? I tried to
compile an i386 bit kernel on an i386 host and I have no issue,
running objdump by hand produces correct output:

$ uname -a
Linux debian32 4.16.0-2-686-pae #1 SMP Debian 4.16.16-1 (2018-06-19)
i686 GNU/Linux
$ objdump -f net/bpfilter/bpfilter_umh |awk -F' |,' '/file
format/{print "-O",$NF} /^architecture:/{print "-B",$2}'
-O elf32-i386
-B i386

then I tried to compile an i386 kernel on an x86_64 host and I get the
same error:

$ make -j8 ARCH=i386
...
  LD      vmlinux.o
ld: i386:x86-64 architecture of input file
`net/bpfilter/bpfilter_umh.o' is incompatible with i386 output
make: *** [Makefile:1015: vmlinux] Error 1

the problem seems to be that bpfilter_umh is compiled with host flags,
and so it's a 64 bit binary in my case:

gcc  -static -o net/bpfilter/bpfilter_umh net/bpfilter/main.o
objcopy -I binary `LC_ALL=C objdump -f net/bpfilter/bpfilter_umh |awk
-F' |,' '/file format/{print "-O",$NF} /^architecture:/{print
"-B",$2}'` --rename-section .data=.init.rodata
net/bpfilter/bpfilter_umh net/bpfilter/bpfilter_umh.o
ld -m elf_i386 -r -o vmlinux.o --whole-archive built-in.a
--no-whole-archive --start-group lib/lib.a arch/x86/lib/lib.a
--end-group
ld: i386:x86-64 architecture of input file
`net/bpfilter/bpfilter_umh.o' is incompatible with i386 output

Any idea how to fix it without building it twice, for host and target?

This presumably has the same root cause that means I can't build a big
endian PowerPC version on a little endian host ...

Either I have to have CONFIG_BPFILTER turned off (or maybe just
CONFIG_BPFILTER_UMH) or build with a compiler that cannot link user
mode programs (which effectively does the same).
-- 
Cheers,
Stephen Rothwell