Re: [PATCH 04/16] net: bpfilter: use 'userprogs' syntax to build bpfilter_umh
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 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 > > > Reported-by: kbuild test robot > > > --- > > > > > > 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.
Re: [PATCH 04/16] net: bpfilter: use 'userprogs' syntax to build bpfilter_umh
On Tue, Jun 30, 2020 at 03:30:04PM +0900, Masahiro Yamada wrote: > On Mon, Jun 8, 2020 at 8:56 PM Michal Kubecek wrote: > > > > 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? > > 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. I wouldn't be very happy with this solution as that would mean adding an extra build dependency which we don't really need. We might even consider disabling CONFIG_BPFILTER_UMH instead. > 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. This wouldn't be a problem for me or openSUSE kernels as we already have CONFIG_BPFILTER_UMH=m. But I can't speak for others, I'm not sure if there are some use cases requiring CONFIG_BPFILTER_UMH=y. Michal
Re: [PATCH 04/16] net: bpfilter: use 'userprogs' syntax to build bpfilter_umh
Hi Michal, Alexei, On Mon, Jun 8, 2020 at 8:56 PM Michal Kubecek 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 > > Reported-by: kbuild test robot > > --- > > > > 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
Re: [PATCH 04/16] net: bpfilter: use 'userprogs' syntax to build bpfilter_umh
On Mon, Jun 8, 2020 at 8:56 PM Michal Kubecek 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 > > Reported-by: kbuild test robot > > --- > > > > 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 Sorry. ifeq was accidentally dropped. I will restore it. -- Best Regards Masahiro Yamada
Re: [PATCH 04/16] net: bpfilter: use 'userprogs' syntax to build bpfilter_umh
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 > Reported-by: kbuild test robot > --- > > 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
