Hi. I have a question about potential bit size mismatch between vmlinux and bpfilter_umh. net/bpfilter/bpfilter_umh is compiled for the default machine bit of the compiler. This may not match to the kernel bit size. This happens in the following scenario. GCC can be compiled as bi-arch. If you use GCC that defaults to 64-bit, you can give -m32 flag to produce the 32 bit code. When you build the kernel for 32-bit, -m32 is properly passed for building the kernel space objects. However, it is missing while building the userspace objects for bpfilter_umh. For example, my build host is x86_64 Ubuntu. If I build the kernel for i386 with CONFIG_BPFILTER_UMH=y, the embedded bpfilter_umh is 64bit ELF. You can reproduce it by the following command on the mainline kernel. masahiro@oscar:~/ref/linux$ make ARCH=i386 defconfig masahiro@oscar:~/ref/linux$ scripts/config -e BPFILTER masahiro@oscar:~/ref/linux$ scripts/config -e BPFILTER_UMH masahiro@oscar:~/ref/linux$ make $(nproc) ARCH=i386 ... masahiro@oscar:~/ref/linux$ file vmlinux vmlinux: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), statically linked, BuildID[sha1]=7ac691c67b4fe9b0cd46b45a2dc2d728d7d87686, not stripped masahiro@oscar:~/ref/linux$ file net/bpfilter/bpfilter_umh net/bpfilter/bpfilter_umh: ELF 64-bit LSB executable, x86-64, version 1 (GNU/Linux), statically linked, BuildID[sha1]=baf1ffe26f4c030a99a945fc22924c8c559e60ac, for GNU/Linux 3.2.0, not stripped At least, the build was successful, but does this work at runtime? If this is a bug, I can fix it cleanly. I think the bit size of the user mode helper should match to the kernel bit size. Is this correct? I noticed this while I was working on userspace build cleanups. https://patchwork.kernel.org/patch/11505207/ -- Best Regards Masahiro Yamada
