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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 8a2cc0505c ("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 b1183b6dca ("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: 8a2cc0505c ("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
This commit is contained in:
Masahiro Yamada 2020-07-01 18:26:44 +09:00 committed by Alexei Starovoitov
parent a4fa458950
commit 9326e0f85b
2 changed files with 8 additions and 4 deletions
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10
net/bpfilter/Kconfig
View File

@ -9,12 +9,14 @@ menuconfig BPFILTER
if BPFILTER if BPFILTER
config BPFILTER_UMH config BPFILTER_UMH
tristate "bpfilter kernel module with user mode helper" 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 default m
help help
This builds bpfilter kernel module with embedded user mode helper This builds bpfilter kernel module with embedded user mode helper
Note: your toolchain must support building static binaries, since Note: To compile this as built-in, your toolchain must support
rootfs isn't mounted at the time when __init functions are called building static binaries, since rootfs isn't mounted at the time
and do_execv won't be able to find the elf interpreter. when __init functions are called and do_execv won't be able to find
the elf interpreter.
endif endif

2
net/bpfilter/Makefile
View File

@ -7,10 +7,12 @@ userprogs := bpfilter_umh
bpfilter_umh-objs := main.o bpfilter_umh-objs := main.o
userccflags += -I $(srctree)/tools/include/ -I $(srctree)/tools/include/uapi userccflags += -I $(srctree)/tools/include/ -I $(srctree)/tools/include/uapi
ifeq ($(CONFIG_BPFILTER_UMH), y)
# builtin bpfilter_umh should be linked with -static # builtin bpfilter_umh should be linked with -static
# since rootfs isn't mounted at the time of __init # since rootfs isn't mounted at the time of __init
# function is called and do_execv won't find elf interpreter # function is called and do_execv won't find elf interpreter
userldflags += -static userldflags += -static
endif
$(obj)/bpfilter_umh_blob.o: $(obj)/bpfilter_umh $(obj)/bpfilter_umh_blob.o: $(obj)/bpfilter_umh