On Tue, Jun 26, 2018 at 08:13:48PM -0700, Alexei Starovoitov wrote:
> From: Masahiro Yamada <yamada.masah...@socionext.com>
>
> What we want here is to embed a user-space program into the kernel.
> Instead of the complex ELF magic, let's simply wrap it in the assembly
> with the '.incbin' directive.
>
> Signed-off-by: Masahiro Yamada <yamada.masah...@socionext.com>
> Signed-off-by: Alexei Starovoitov <a...@kernel.org>
> ---
> I think this patch should 'fix' bpfilter build issue on all archs.
> cflags for cross CC may still be incorrect and embedded blob
> may fail to execute via fork_usermode_blob()
> (like in case of 'make ARCH=i386 net/bpfilter/' CC will build and link 64-bit
> binary that will be included into bpfilter.o or vmlinux and that binary
> will fail to run on 32-bit kernel),
> but that is separate issue that will be addressed in net-next time frame.
> Long term we've discussed to switch to something like klibc and keep it
> as part of the kernel to avoid relying on glibc and cc-can-link.sh.
>
At the very least it fixes the build issue when building i386 images
on x86_64 systems.
(Build-)Tested-by: Guenter Roeck <li...@roeck-us.net>
> net/bpfilter/Makefile | 17 ++---------------
> net/bpfilter/bpfilter_kern.c | 11 +++++------
> net/bpfilter/bpfilter_umh_blob.S | 7 +++++++
> 3 files changed, 14 insertions(+), 21 deletions(-)
> create mode 100644 net/bpfilter/bpfilter_umh_blob.S
>
> diff --git a/net/bpfilter/Makefile b/net/bpfilter/Makefile
> index 051dc18b8ccb..39c6980b5d99 100644
> --- a/net/bpfilter/Makefile
> +++ b/net/bpfilter/Makefile
> @@ -15,20 +15,7 @@ ifeq ($(CONFIG_BPFILTER_UMH), y)
> HOSTLDFLAGS += -static
> endif
>
> -# a bit of elf magic to convert bpfilter_umh binary into a binary blob
> -# inside bpfilter_umh.o elf file referenced by
> -# _binary_net_bpfilter_bpfilter_umh_start symbol
> -# 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 \
> - `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 $< $@
> -
> -$(obj)/bpfilter_umh.o: $(obj)/bpfilter_umh
> - $(call cmd,copy_umh)
> +$(obj)/bpfilter_umh_blob.o: $(obj)/bpfilter_umh
>
> obj-$(CONFIG_BPFILTER_UMH) += bpfilter.o
> -bpfilter-objs += bpfilter_kern.o bpfilter_umh.o
> +bpfilter-objs += bpfilter_kern.o bpfilter_umh_blob.o
> diff --git a/net/bpfilter/bpfilter_kern.c b/net/bpfilter/bpfilter_kern.c
> index 09522573f611..f0fc182d3db7 100644
> --- a/net/bpfilter/bpfilter_kern.c
> +++ b/net/bpfilter/bpfilter_kern.c
> @@ -10,11 +10,8 @@
> #include <linux/file.h>
> #include "msgfmt.h"
>
> -#define UMH_start _binary_net_bpfilter_bpfilter_umh_start
> -#define UMH_end _binary_net_bpfilter_bpfilter_umh_end
> -
> -extern char UMH_start;
> -extern char UMH_end;
> +extern char bpfilter_umh_start;
> +extern char bpfilter_umh_end;
>
> static struct umh_info info;
> /* since ip_getsockopt() can run in parallel, serialize access to umh */
> @@ -93,7 +90,9 @@ static int __init load_umh(void)
> int err;
>
> /* fork usermode process */
> - err = fork_usermode_blob(&UMH_start, &UMH_end - &UMH_start, &info);
> + err = fork_usermode_blob(&bpfilter_umh_start,
> + &bpfilter_umh_end - &bpfilter_umh_start,
> + &info);
> if (err)
> return err;
> pr_info("Loaded bpfilter_umh pid %d\n", info.pid);
> diff --git a/net/bpfilter/bpfilter_umh_blob.S
> b/net/bpfilter/bpfilter_umh_blob.S
> new file mode 100644
> index 000000000000..40311d10d2f2
> --- /dev/null
> +++ b/net/bpfilter/bpfilter_umh_blob.S
> @@ -0,0 +1,7 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> + .section .init.rodata, "a"
> + .global bpfilter_umh_start
> +bpfilter_umh_start:
> + .incbin "net/bpfilter/bpfilter_umh"
> + .global bpfilter_umh_end
> +bpfilter_umh_end:
