Commit 9371f86e authored by Masahiro Yamada's avatar Masahiro Yamada
Browse files

bpfilter: match bit size of bpfilter_umh to that of the kernel 



bpfilter_umh is built for the default machine bit of the compiler,
which may not match to the bit size of the kernel.

This happens in the scenario below:

You can use biarch GCC that defaults to 64-bit for building the 32-bit
kernel. In this case, Kbuild passes -m32 to teach the compiler to
produce 32-bit kernel space objects. However, it is missing when
building bpfilter_umh. It is built as a 64-bit ELF, and then embedded
into the 32-bit kernel.

The 32-bit kernel and 64-bit umh is a bad combination.

In theory, we can have 32-bit umh running on 64-bit kernel, but we do
not have a good reason to support such a usecase.

The best is to match the bit size between them.

Pass -m32 or -m64 to the umh build command if it is found in
$(KBUILD_CFLAGS). Evaluate CC_CAN_LINK against the kernel bit-size.

Signed-off-by: default avatarMasahiro Yamada <masahiroy@kernel.org>
parent 59721d4e

init/Kconfig

+3 −1
Original line number Diff line number Diff line
@@ -45,7 +45,9 @@ config CLANG_VERSION 
	default $(shell,$(srctree)/scripts/clang-version.sh $(CC))



config CC_CAN_LINK

	def_bool $(success,$(srctree)/scripts/cc-can-link.sh $(CC))

	bool

	default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(m64-flag)) if 64BIT

	default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) $(m32-flag))



config CC_HAS_ASM_GOTO

	def_bool $(success,$(srctree)/scripts/gcc-goto.sh $(CC))

net/bpfilter/Makefile

+3 −2
Original line number Diff line number Diff line
@@ -5,14 +5,15 @@ 


hostprogs := bpfilter_umh

bpfilter_umh-objs := main.o

KBUILD_HOSTCFLAGS += -I $(srctree)/tools/include/ -I $(srctree)/tools/include/uapi

KBUILD_HOSTCFLAGS += -I $(srctree)/tools/include/ -I $(srctree)/tools/include/uapi \

			$(filter -m32 -m64, $(KBUILD_CFLAGS))

HOSTCC := $(CC)



ifeq ($(CONFIG_BPFILTER_UMH), y)

# builtin bpfilter_umh should be compiled 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

KBUILD_HOSTLDFLAGS += -static $(filter -m32 -m64, $(KBUILD_CFLAGS))

endif



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

usr/include/Makefile

+4 −0
Original line number Diff line number Diff line
@@ -8,6 +8,10 @@ 
# We cannot go as far as adding -Wpedantic since it emits too many warnings.

UAPI_CFLAGS := -std=c90 -Wall -Werror=implicit-function-declaration



# In theory, we do not care -m32 or -m64 for header compile tests.

# It is here just because CONFIG_CC_CAN_LINK is tested with -m32 or -m64.

UAPI_CFLAGS += $(filter -m32 -m64, $(KBUILD_CFLAGS))



override c_flags = $(UAPI_CFLAGS) -Wp,-MMD,$(depfile) -I$(objtree)/usr/include



# The following are excluded for now because they fail to build.

CRA Git | Maintained and supported by SUSTech CRA and CCSE