On Thu, Jan 3, 2019 at 1:36 AM Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx> wrote: > > On Wed, Jan 2, 2019 at 9:14 PM Sedat Dilek <sedat.dilek@xxxxxxxxx> wrote: > > > > Hi, > > > > I was not aware that CONFIG_JUMP_LABEL Kconfig setting depends on the > > support of asm-goto. > > > > Currently, I am doing experiments with clang-7 and a snapshot of > > clang-8 on Linux/x86. > > These compilers have no asm-goto support. > > > > What is your recommendation for Linux >= v4.20? > > I am asking as it is possible to set CONFIG_JUMP_LABEL=y when > > compiling with clang - which has no effect. > > This is confusing. > > > > Thanks, this patch makes things clearer and protects users from > > setting "wrong" in the sense of non-functional settings. > > > > I have tested this against recent Linus tree where kbuild/kconfig Git > > pulls were latest commits. > > > > Tested-by: Sedat Dilek <sedat.dilek@xxxxxxxxx> [ x86 with LLVM/Clang > > v7 and v8 (snapshot) ] > > > Which part was tested? > > x86 kernel cannot be compiled with Clang > since it lacks the asm-goto support. > > > $ make CC=clang > Compiler lacks asm-goto support. > arch/x86/Makefile:293: recipe for target 'checkbin' failed > make: *** [checkbin] Error 1 > Yes, this needs a workaround (see attachment). As a base I took kbuid.git#for-next on top of Linux v4.20... $ git log --oneline -2 58609f06cfb6 (HEAD -> 4.20.0-2-amd64-cbl) x86: Workaround clang does not support asm-goto 68af7c873957 (for-4.20/kbuild-next-20190103) kbuild: remove unnecessary stubs for archheader and archscripts ...and includes: f44251005047 jump_label: move 'asm goto' support test to Kconfig My compiler is clang-7 from Debian/testing. $ git log --oneline -2 58609f06cfb6 (HEAD -> 4.20.0-2-amd64-cbl) x86: Workaround clang does not support asm-goto 68af7c873957 (for-4.20/kbuild-next-20190103) kbuild: remove unnecessary stubs for archheader and archscripts It's compile-tested only on Debian/testing AMD64. I cannot boot into bare metal. This might have other root causes. - Sedat - P.S.: Additional informations Booting in QEMU 3.1 shows... $ ./run_qemu.sh Probing EDD (edd=off to disable)... ok XZ-compressed data is corrupt -- System haltedqemu-system-x86_64: terminating on signal 2 $ cat run_qemu.sh KPATH=$(pwd) qemu-system-x86_64 -enable-kvm -M pc -kernel $KPATH/bzImage -initrd $KPATH/initrd.img -m 512 -net none -serial stdio -append "root=/dev/ram0 console=ttyS0 hung_task_panic=1 earlyprintk=ttyS0,115200" NOTE: I can boot a Linux v4.20 kernel with this QEMU version.
From 53727072385d3e9327e2f7c466b49078b09286ae Mon Sep 17 00:00:00 2001 From: Sedat Dilek <sedat.dilek@xxxxxxxxxxx> Date: Thu, 3 Jan 2019 15:03:12 +0100 Subject: [PATCH] x86: Workaround clang does not support asm-goto Only warn once that Clang does not support asm-goto (see LLVM bug #9295). Avoid and thus reduce warnings by adding '-D__BPF_TRACING__' argument to KBUILD_CFLAGS where needed (inspired by [1]). Testing: The patch "jump_label: move 'asm goto' support test to Kconfig" from [2]. [1] https://github.com/ClangBuiltLinux/continuous-integration/blob/master/patches/linux/x86_64/0001-DO-NOT-UPSTREAM-x86-Avoid-warnings-errors-due-to-lac.patch [2] https://lore.kernel.org/patchwork/patch/1028282/ [3] https://github.com/ClangBuiltLinux/linux/issues/6 --- arch/x86/Makefile | 5 +++-- arch/x86/boot/compressed/Makefile | 4 ++++ arch/x86/include/asm/cpufeature.h | 8 -------- drivers/firmware/efi/libstub/Makefile | 4 ++++ 4 files changed, 11 insertions(+), 10 deletions(-) diff --git a/arch/x86/Makefile b/arch/x86/Makefile index 9c5a67d1b9c1..ba8ee0de0397 100644 --- a/arch/x86/Makefile +++ b/arch/x86/Makefile @@ -290,8 +290,9 @@ vdso_install: archprepare: checkbin checkbin: ifndef CONFIG_CC_HAS_ASM_GOTO - @echo Compiler lacks asm-goto support. - @exit 1 + @echo Warning: Compiler lacks asm-goto support. + @exit 0 +KBUILD_CFLAGS += -D__BPF_TRACING__ endif ifdef CONFIG_RETPOLINE ifeq ($(RETPOLINE_CFLAGS),) diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile index 466f66c8a7f8..bc8991fede60 100644 --- a/arch/x86/boot/compressed/Makefile +++ b/arch/x86/boot/compressed/Makefile @@ -39,6 +39,10 @@ KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member) KBUILD_CFLAGS += $(call cc-disable-warning, gnu) KBUILD_CFLAGS += -Wno-pointer-sign +ifndef CONFIG_CC_HAS_ASM_GOTO +KBUILD_CFLAGS += -D__BPF_TRACING__ +endif + KBUILD_AFLAGS := $(KBUILD_CFLAGS) -D__ASSEMBLY__ GCOV_PROFILE := n UBSAN_SANITIZE :=n diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h index ce95b8cbd229..4774fafee82b 100644 --- a/arch/x86/include/asm/cpufeature.h +++ b/arch/x86/include/asm/cpufeature.h @@ -142,14 +142,6 @@ extern void clear_cpu_cap(struct cpuinfo_x86 *c, unsigned int bit); #if defined(__clang__) && !defined(CONFIG_CC_HAS_ASM_GOTO) -/* - * Workaround for the sake of BPF compilation which utilizes kernel - * headers, but clang does not support ASM GOTO and fails the build. - */ -#ifndef __BPF_TRACING__ -#warning "Compiler lacks ASM_GOTO support. Add -D __BPF_TRACING__ to your compiler arguments" -#endif - #define static_cpu_has(bit) boot_cpu_has(bit) #else diff --git a/drivers/firmware/efi/libstub/Makefile b/drivers/firmware/efi/libstub/Makefile index d9845099635e..68ff33dc075d 100644 --- a/drivers/firmware/efi/libstub/Makefile +++ b/drivers/firmware/efi/libstub/Makefile @@ -24,6 +24,10 @@ cflags-$(CONFIG_ARM) := $(subst -pg,,$(KBUILD_CFLAGS)) \ cflags-$(CONFIG_EFI_ARMSTUB) += -I$(srctree)/scripts/dtc/libfdt +ifndef CONFIG_CC_HAS_ASM_GOTO +cflags-$(CONFIG_X86) += -D__BPF_TRACING__ +endif + KBUILD_CFLAGS := $(cflags-y) -DDISABLE_BRANCH_PROFILING \ -D__NO_FORTIFY \ $(call cc-option,-ffreestanding) \ -- 2.20.1
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