From mboxrd@z Thu Jan 1 00:00:00 1970 From: haokexin@gmail.com (Kevin Hao) Date: Thu, 15 Jan 2015 20:07:33 +0800 Subject: [PATCH v2] arm64: kill off the libgcc dependency Message-ID: <1421323653-27214-1-git-send-email-haokexin@gmail.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org The arm64 kernel builds fine without the libgcc. Actually it should not be used at all in the kernel. The following are the reasons indicated by Russell King: Although libgcc is part of the compiler, libgcc is built with the expectation that it will be running in userland - it expects to link to a libc. That's why you can't build libgcc without having the glibc headers around. For example, on ARM, libgcc.a may contain calls to __div0, and it may provide its own __div0 implementation, which invokes various Linux system calls. Various functions reference _GLOBAL_OFFSET_TABLE_ which we don't want to have in the kernel. Depending on how the compiler was built, libgcc.a may be built for ARMv4, ARMv5, ARMv6 or ARMv7, and may not be appropriate for linking with the kernel. (Eg, you wouldn't want to try to link an ARMv7 libgcc.a in an ARMv5 kernel - and we /really/ don't want the mess of having different toolchains for different ARM arch versions.) It may also drag in the userspace exception unwind support. Meanwhile, having the kernel build the compiler support functions that it needs ensures that (a) we know what compiler support functions are being used, (b) we know the implementation of those support functions are sane for use in the kernel, (c) we can build them with appropriate compiler flags for best performance, and (d) we remove an unnecessary dependency on the build toolchain. Signed-off-by: Kevin Hao Acked-by: Will Deacon --- v2: - Update the commit log. - Add ack from Will. arch/arm64/Makefile | 3 --- 1 file changed, 3 deletions(-) diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile index 1c43cec971b5..a20c28348be4 100644 --- a/arch/arm64/Makefile +++ b/arch/arm64/Makefile @@ -15,8 +15,6 @@ CPPFLAGS_vmlinux.lds = -DTEXT_OFFSET=$(TEXT_OFFSET) OBJCOPYFLAGS :=-O binary -R .note -R .note.gnu.build-id -R .comment -S GZFLAGS :=-9 -LIBGCC := $(shell $(CC) $(KBUILD_CFLAGS) -print-libgcc-file-name) - KBUILD_DEFCONFIG := defconfig KBUILD_CFLAGS += -mgeneral-regs-only @@ -50,7 +48,6 @@ core-$(CONFIG_KVM) += arch/arm64/kvm/ core-$(CONFIG_XEN) += arch/arm64/xen/ core-$(CONFIG_CRYPTO) += arch/arm64/crypto/ libs-y := arch/arm64/lib/ $(libs-y) -libs-y += $(LIBGCC) libs-$(CONFIG_EFI_STUB) += drivers/firmware/efi/libstub/ # Default target when executing plain make -- 1.9.3