From 9371f86ecb60f6f1f120e3d93fe892bbb70d04c0 Mon Sep 17 00:00:00 2001 From: Masahiro Yamada Date: Wed, 29 Apr 2020 12:45:13 +0900 Subject: 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: Masahiro Yamada --- net/bpfilter/Makefile | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) (limited to 'net') diff --git a/net/bpfilter/Makefile b/net/bpfilter/Makefile index 36580301da70..f6209e4827b9 100644 --- a/net/bpfilter/Makefile +++ b/net/bpfilter/Makefile @@ -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 -- cgit v1.2.3-59-g8ed1b From b1183b6dca3e0d59ce8fa81767def6ea6188e8ec Mon Sep 17 00:00:00 2001 From: Masahiro Yamada Date: Sat, 9 May 2020 16:39:15 +0900 Subject: bpfilter: check if $(CC) can link static libc in Kconfig On Fedora, linking static glibc requires the glibc-static RPM package, which is not part of the glibc-devel package. CONFIG_CC_CAN_LINK does not check the capability of static linking, so you can enable CONFIG_BPFILTER_UMH, then fail to build: HOSTLD net/bpfilter/bpfilter_umh /usr/bin/ld: cannot find -lc collect2: error: ld returned 1 exit status Add CONFIG_CC_CAN_LINK_STATIC, and make CONFIG_BPFILTER_UMH depend on it. Reported-by: Valdis Kletnieks Signed-off-by: Masahiro Yamada Acked-by: Alexei Starovoitov --- init/Kconfig | 5 +++++ net/bpfilter/Kconfig | 2 +- 2 files changed, 6 insertions(+), 1 deletion(-) (limited to 'net') diff --git a/init/Kconfig b/init/Kconfig index b2ce83c2e84c..fb8ab85de7f8 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -49,6 +49,11 @@ config CC_CAN_LINK 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_CAN_LINK_STATIC + bool + default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) -static $(m64-flag)) if 64BIT + default $(success,$(srctree)/scripts/cc-can-link.sh $(CC) -static $(m32-flag)) + config CC_HAS_ASM_GOTO def_bool $(success,$(srctree)/scripts/gcc-goto.sh $(CC)) diff --git a/net/bpfilter/Kconfig b/net/bpfilter/Kconfig index fed9290e3b41..045144d4a42c 100644 --- a/net/bpfilter/Kconfig +++ b/net/bpfilter/Kconfig @@ -9,7 +9,7 @@ menuconfig BPFILTER if BPFILTER config BPFILTER_UMH tristate "bpfilter kernel module with user mode helper" - depends on CC_CAN_LINK + depends on CC_CAN_LINK_STATIC default m help This builds bpfilter kernel module with embedded user mode helper -- cgit v1.2.3-59-g8ed1b From 8a2cc0505cc4313e6ce2bc8fc1ce3607b410e114 Mon Sep 17 00:00:00 2001 From: Masahiro Yamada Date: Wed, 29 Apr 2020 12:45:15 +0900 Subject: bpfilter: use 'userprogs' syntax to build bpfilter_umh The user mode helper should be compiled for the same architecture as the kernel. This Makefile reused the 'hostprogs' syntax by overriding HOSTCC with CC. Use the new syntax 'userprogs' to fix the Makefile mess. Signed-off-by: Masahiro Yamada Acked-by: Sam Ravnborg --- net/bpfilter/Makefile | 12 ++++-------- 1 file changed, 4 insertions(+), 8 deletions(-) (limited to 'net') diff --git a/net/bpfilter/Makefile b/net/bpfilter/Makefile index f6209e4827b9..f23b53294fba 100644 --- a/net/bpfilter/Makefile +++ b/net/bpfilter/Makefile @@ -3,18 +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 \ - $(filter -m32 -m64, $(KBUILD_CFLAGS)) -HOSTCC := $(CC) +userccflags += -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 $(filter -m32 -m64, $(KBUILD_CFLAGS)) -endif +userldflags += -static $(obj)/bpfilter_umh_blob.o: $(obj)/bpfilter_umh -- cgit v1.2.3-59-g8ed1b From 9f64fbdb774838db1445268fa8c46041fb1c28ab Mon Sep 17 00:00:00 2001 From: Valdis Kl ē tnieks Date: Sat, 9 May 2020 00:47:19 -0400 Subject: bpfilter: document build requirements for bpfilter_umh It's not intuitively obvious that bpfilter_umh is a statically linked binary. Mention the toolchain requirement in the Kconfig help, so people have an easier time figuring out what's needed. Signed-off-by: Valdis Kletnieks Signed-off-by: Masahiro Yamada --- net/bpfilter/Kconfig | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'net') diff --git a/net/bpfilter/Kconfig b/net/bpfilter/Kconfig index 045144d4a42c..84015ef3ee27 100644 --- a/net/bpfilter/Kconfig +++ b/net/bpfilter/Kconfig @@ -13,4 +13,8 @@ config BPFILTER_UMH 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. endif -- cgit v1.2.3-59-g8ed1b