On Tue, Jun 30, 2020 at 03:30:04PM +0900, Masahiro Yamada wrote: > Hi Michal, Alexei, > > On Mon, Jun 8, 2020 at 8:56 PM Michal Kubecek <mkubecek@xxxxxxx> wrote: > > > > On Thu, Apr 23, 2020 at 04:39:17PM +0900, Masahiro Yamada wrote: > > > The user mode helper should be compiled for the same architecture as > > > the kernel. > > > > > > This Makefile reuses the 'hostprogs' syntax by overriding HOSTCC with CC. > > > > > > Now that Kbuild provides the syntax 'userprogs', use it to fix the > > > Makefile mess. > > > > > > Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx> > > > Reported-by: kbuild test robot <lkp@xxxxxxxxx> > > > --- > > > > > > net/bpfilter/Makefile | 11 ++++------- > > > 1 file changed, 4 insertions(+), 7 deletions(-) > > > > > > diff --git a/net/bpfilter/Makefile b/net/bpfilter/Makefile > > > index 36580301da70..6ee650c6badb 100644 > > > --- a/net/bpfilter/Makefile > > > +++ b/net/bpfilter/Makefile > > > @@ -3,17 +3,14 @@ > > > # Makefile for the Linux BPFILTER layer. > > > # > > > > > > -hostprogs := bpfilter_umh > > > +userprogs := bpfilter_umh > > > bpfilter_umh-objs := main.o > > > -KBUILD_HOSTCFLAGS += -I $(srctree)/tools/include/ -I $(srctree)/tools/include/uapi > > > -HOSTCC := $(CC) > > > +user-ccflags += -I $(srctree)/tools/include/ -I $(srctree)/tools/include/uapi > > > > > > -ifeq ($(CONFIG_BPFILTER_UMH), y) > > > -# builtin bpfilter_umh should be compiled with -static > > > +# builtin bpfilter_umh should be linked with -static > > > # since rootfs isn't mounted at the time of __init > > > # function is called and do_execv won't find elf interpreter > > > -KBUILD_HOSTLDFLAGS += -static > > > -endif > > > +bpfilter_umh-ldflags += -static > > > > > > $(obj)/bpfilter_umh_blob.o: $(obj)/bpfilter_umh > > > > Hello, > > > > I just noticed that this patch (now in mainline as commit 8a2cc0505cc4) > > drops the test if CONFIG_BPFILTER_UMH is "y" so that -static is now > > passed to the linker even if bpfilter_umh is built as a module which > > wasn't the case in v5.7. > > > > This is not mentioned in the commit message and the comment still says > > "*builtin* bpfilter_umh should be linked with -static" so this change > > doesn't seem to be intentional. Did I miss something? > > > > Michal Kubecek > > I was away for a while from this because I saw long discussion in > "net/bpfilter: Remove this broken and apparently unmaintained" > > > Please let me resume this topic now. > > > The original behavior of linking umh was like this: > - If CONFIG_BPFILTER_UMH=y, bpfilter_umh was linked with -static > - If CONFIG_BPFILTER_UMH=m, bpfilter_umh was linked without -static That was done to make sure both static and dynamic linking work. For production -static is necessary. For debugging of usermode blob dynamic is beneficial. > Restoring the original behavior will add more complexity because > now we have CONFIG_CC_CAN_LINK and CONFIG_CC_CAN_LINK_STATIC > since commit b1183b6dca3e0d5 > > If CONFIG_BPFILTER_UMH=y, we need to check CONFIG_CC_CAN_LINK_STATIC. > If CONFIG_BPFILTER_UMH=m, we need to check CONFIG_CC_CAN_LINK. > This would make the Kconfig dependency logic too complicated. Currently I'm working on adding bpf_iter to use 'user mode driver' (old user mode blob) facility on top of Eric's patches. So there will be quite a bit more complexity to build system. Folks who don't want to deal with -static requirement should just disable the feature. > To make it simpler, I'd like to suggest two options. > > > > Idea 1: > > Always use -static irrespective of whether > CONFIG_BPFILTER_UMH is y or m. I don't think it's making it much simpler. It's a tiny change to makefile. I could be missing something. Requiring -static for =y and =m is fine. > Add two more lines to clarify this > in the comment in net/bpfilter/Makefile: > > # builtin bpfilter_umh should be linked with -static > # since rootfs isn't mounted at the time of __init > # function is called and do_execv won't find elf interpreter. > # Static linking is not required when bpfilter is modular, but > # we always pass -static to keep the 'depends on' in Kconfig simple. > > > > Idea 2: > > Allow umh to become only modular, > and drop -static flag entirely. absolutely not. Both =y and =m are mandatory. > > If you look at net/bpfilter/Kconfig, > BPFILTER_UMH already has 'default m'. > So, I assume the most expected use-case > is modular. The default for BPFILTER is =N. Distros should NOT be turning that to =y Same thing with upcoming bpf_iter. It will default to =n.
