Netdev Archive on lore.kernel.org
 help / color / Atom feed
From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Masahiro Yamada <masahiroy@kernel.org>
Cc: Michal Kubecek <mkubecek@suse.cz>,
	Alexei Starovoitov <ast@kernel.org>,
	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 09:47:08 -0700
Message-ID: <20200630164708.aeuoq4ruhivu5o2d@ast-mbp.dhcp.thefacebook.com> (raw)
In-Reply-To: <CAK7LNARGKCyWbfWUOX3nLLOBS3gi1QU3acdXLPVK4C+ErMDLpA@mail.gmail.com>

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@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

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.

  parent reply index

Thread overview: 13+ 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 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
2020-06-08 11:56   ` Michal Kubecek
2020-06-08 13:32     ` Masahiro Yamada
2020-06-30  6:30     ` Masahiro Yamada
2020-06-30  8:57       ` Michal Kubecek
2020-06-30 16:47       ` Alexei Starovoitov [this message]
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
2020-04-25 11:53 ` [PATCH 00/16] kbuild: support 'userprogs' syntax Sam Ravnborg
2020-04-29  2:38   ` Masahiro Yamada

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20200630164708.aeuoq4ruhivu5o2d@ast-mbp.dhcp.thefacebook.com \
    --to=alexei.starovoitov@gmail.com \
    --cc=andriin@fb.com \
    --cc=ast@kernel.org \
    --cc=bpf@vger.kernel.org \
    --cc=daniel@iogearbox.net \
    --cc=davem@davemloft.net \
    --cc=john.fastabend@gmail.com \
    --cc=kafai@fb.com \
    --cc=kpsingh@chromium.org \
    --cc=kuba@kernel.org \
    --cc=linux-kbuild@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=masahiroy@kernel.org \
    --cc=mkubecek@suse.cz \
    --cc=netdev@vger.kernel.org \
    --cc=sam@ravnborg.org \
    --cc=songliubraving@fb.com \
    --cc=yhs@fb.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Netdev Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/netdev/0 netdev/git/0.git
	git clone --mirror https://lore.kernel.org/netdev/1 netdev/git/1.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 netdev netdev/ https://lore.kernel.org/netdev \
		netdev@vger.kernel.org
	public-inbox-index netdev

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.netdev


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git