Commit 9326e0f8 authored Jul 01, 2020 by Masahiro Yamada Committed by Alexei Starovoitov Jul 14, 2020

bpfilter: Allow to build bpfilter_umh as a module without static library



Originally, bpfilter_umh was linked with -static only when
CONFIG_BPFILTER_UMH=y.

Commit 8a2cc050 ("bpfilter: use 'userprogs' syntax to build
bpfilter_umh") silently, accidentally dropped the CONFIG_BPFILTER_UMH=y
test in the Makefile. Revive it in order to link it dynamically when
CONFIG_BPFILTER_UMH=m.

Since commit b1183b6d ("bpfilter: check if $(CC) can link static
libc in Kconfig"), the compiler must be capable of static linking to
enable CONFIG_BPFILTER_UMH, but it requires more than needed.

To loosen the compiler requirement, I changed the dependency as follows:

    depends on CC_CAN_LINK
    depends on m || CC_CAN_LINK_STATIC

If CONFIG_CC_CAN_LINK_STATIC in unset, CONFIG_BPFILTER_UMH is restricted
to 'm' or 'n'.

In theory, CONFIG_CC_CAN_LINK is not required for CONFIG_BPFILTER_UMH=y,
but I did not come up with a good way to describe it.

Fixes: 8a2cc050 ("bpfilter: use 'userprogs' syntax to build bpfilter_umh")
Reported-by: Michal Kubecek <mkubecek@suse.cz>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Tested-by: Michal Kubecek <mkubecek@suse.cz>
Link: https://lore.kernel.org/bpf/20200701092644.762234-1-masahiroy@kernel.org

parent a4fa4589

net/bpfilter/Kconfig

+6 −4

Original line number	Diff line number	Diff line
		@@ -9,12 +9,14 @@ menuconfig BPFILTER
		if BPFILTER
		config BPFILTER_UMH
		tristate "bpfilter kernel module with user mode helper"
		depends on CC_CAN_LINK_STATIC
		depends on CC_CAN_LINK
		depends on m \|\| CC_CAN_LINK_STATIC
		default m
		help
		This builds bpfilter kernel module with embedded user mode helper

		Note: your toolchain must support building static binaries, since
		rootfs isn't mounted at the time when __init functions are called
		and do_execv won't be able to find the elf interpreter.
		Note: To compile this as built-in, your toolchain must support
		building static binaries, since rootfs isn't mounted at the time
		when __init functions are called and do_execv won't be able to find
		the elf interpreter.
		endif

net/bpfilter/Makefile

+2 −0

Original line number	Diff line number	Diff line
		@@ -7,10 +7,12 @@ userprogs := bpfilter_umh
		bpfilter_umh-objs := main.o
		userccflags += -I $(srctree)/tools/include/ -I $(srctree)/tools/include/uapi

		ifeq ($(CONFIG_BPFILTER_UMH), y)
		# 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
		userldflags += -static
		endif

		$(obj)/bpfilter_umh_blob.o: $(obj)/bpfilter_umh

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