From: Masahiro Yamada <masahiroy@kernel.org>
To: Michal Kubecek <mkubecek@suse.cz>, Alexei Starovoitov <ast@kernel.org>
Cc: Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
bpf <bpf@vger.kernel.org>, Sam Ravnborg <sam@ravnborg.org>,
Andrii Nakryiko <andriin@fb.com>,
Daniel Borkmann <daniel@iogearbox.net>,
"David S. Miller" <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>,
John Fastabend <john.fastabend@gmail.com>,
KP Singh <kpsingh@chromium.org>, Martin KaFai Lau <kafai@fb.com>,
Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Networking <netdev@vger.kernel.org>
Subject: Re: [PATCH 04/16] net: bpfilter: use 'userprogs' syntax to build bpfilter_umh
Date: Tue, 30 Jun 2020 15:30:04 +0900 [thread overview]
Message-ID: <CAK7LNARGKCyWbfWUOX3nLLOBS3gi1QU3acdXLPVK4C+ErMDLpA@mail.gmail.com> (raw)
In-Reply-To: <20200608115628.osizkpo76cgn2ci7@lion.mk-sys.cz>
Hi Michal, Alexei,
On Mon, Jun 8, 2020 at 8:56 PM Michal Kubecek <mkubecek@suse.cz> 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@kernel.org>
> > Reported-by: kbuild test robot <lkp@intel.com>
> > ---
> >
> > 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
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.
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.
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.
If you look at net/bpfilter/Kconfig,
BPFILTER_UMH already has 'default m'.
So, I assume the most expected use-case
is modular.
My suggestion is to replace 'default m' with 'depends on m'.
config BPFILTER_UMH
tristate "bpfilter kernel module with user mode helper"
depends on CC_CAN_LINK
depends on m
Then BPFILTER_UMH will be restricted to either m or n.
Link umh dynamically because we can expect rootfs
is already mounted for the module case.
Comments are appreciated.
--
Best Regards
Masahiro Yamada
next prev parent reply other threads:[~2020-06-30 6:41 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-23 7:39 [PATCH 00/16] kbuild: support 'userprogs' syntax Masahiro Yamada
2020-04-23 7:39 ` [PATCH 01/16] Documentation: kbuild: fix the section title format Masahiro Yamada
2020-04-23 7:39 ` [PATCH 02/16] Revert "objtool: Skip samples subdirectory" Masahiro Yamada
2020-04-24 20:32 ` Josh Poimboeuf
2020-04-29 2:43 ` Masahiro Yamada
2020-04-23 7:39 ` [PATCH 03/16] kbuild: add infrastructure to build userspace programs Masahiro Yamada
2020-04-23 15:15 ` Masahiro Yamada
2020-04-23 7:39 ` [PATCH 04/16] net: bpfilter: use 'userprogs' syntax to build bpfilter_umh Masahiro Yamada
2020-04-28 1:46 ` kbuild test robot
2020-04-28 5:13 ` Masahiro Yamada
2020-06-08 11:56 ` Michal Kubecek
2020-06-08 13:32 ` Masahiro Yamada
2020-06-30 6:30 ` Masahiro Yamada [this message]
2020-06-30 8:57 ` Michal Kubecek
2020-06-30 16:47 ` Alexei Starovoitov
2020-04-23 7:39 ` [PATCH 05/16] samples: seccomp: build sample programs for target architecture Masahiro Yamada
2020-04-23 7:39 ` [PATCH 06/16] kbuild: doc: document the new syntax 'userprogs' Masahiro Yamada
2020-04-23 7:39 ` [PATCH 07/16] samples: uhid: fix warnings in uhid-example Masahiro Yamada
2020-04-23 7:39 ` [PATCH 08/16] samples: uhid: build sample program for target architecture Masahiro Yamada
2020-04-23 7:39 ` [PATCH 09/16] samples: hidraw: " Masahiro Yamada
2020-04-23 7:39 ` [PATCH 10/16] samples: connector: " Masahiro Yamada
2020-04-23 7:39 ` [PATCH 11/16] samples: vfs: build sample programs " Masahiro Yamada
2020-04-23 7:39 ` [PATCH 12/16] samples: pidfd: build sample program " Masahiro Yamada
2020-04-23 7:39 ` [PATCH 13/16] samples: mei: " Masahiro Yamada
2020-04-23 7:39 ` [PATCH 14/16] samples: auxdisplay: use 'userprogs' syntax Masahiro Yamada
2020-04-23 11:50 ` Miguel Ojeda
2020-04-24 2:59 ` Masahiro Yamada
2020-04-23 7:39 ` [PATCH 15/16] samples: timers: " Masahiro Yamada
2020-04-23 7:39 ` [PATCH 16/16] samples: watchdog: " Masahiro Yamada
2020-04-25 11:53 ` [PATCH 00/16] kbuild: support " Sam Ravnborg
2020-04-29 2:38 ` Masahiro Yamada
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