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Wed, 05 Aug 2026 11:55:58 -0700 (PDT) From: Matt Turner To: Richard Henderson , Matt Turner , Magnus Lindholm , Nathan Chancellor , Nick Desaulniers , Bill Wendling , Justin Stitt , Nicolas Schier Cc: linux-alpha@vger.kernel.org, linux-kernel@vger.kernel.org, llvm@lists.linux.dev, linux-kbuild@vger.kernel.org Subject: [PATCH v2 1/2] alpha: pass -Wa,-mev6 only when using GNU as Date: Wed, 5 Aug 2026 14:55:57 -0400 Message-ID: <20260805185557.3283233-1-mattst88@gmail.com> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260803-alpha-clang-v1-0-1c4ba5ba7a64@gmail.com> References: <20260803-alpha-clang-v1-0-1c4ba5ba7a64@gmail.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" That flag exists to stop gas emulating instructions the assembler thinks the target lacks. It is a gas-only option, and LLVM's integrated assembler does not emulate instructions in the first place, so nothing is needed there. Condition it on CONFIG_AS_IS_GNU rather than the compiler, so it is still passed for clang builds using GNU as (LLVM_IAS=3D0) and omitted only for the integrated assembler. Signed-off-by: Matt Turner Reviewed-by: Magnus Lindholm linmag7@gmail.com --- Only this patch changed; patch 2/2 ("alpha: read $gp and $sp explicitly for clang") is unchanged from v1 and is not resent. Changes in v2: - Drop the scripts/Makefile.clang CLANG_TARGET_FLAGS_alpha entry. It will be sent separately when the alpha backend is upstreamed to LLVM. - Condition -Wa,-mev6 on CONFIG_AS_IS_GNU rather than CONFIG_CC_IS_GCC, so it is still passed for clang builds using GNU as (LLVM_IAS=3D0). - Reword the subject and commit message for the reduced scope. - Link to v1: https://lore.kernel.org/r/20260803-alpha-clang-v1-0-1c4ba5ba7= a64@gmail.com arch/alpha/Makefile | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/arch/alpha/Makefile b/arch/alpha/Makefile index 35445ff2e489..7074602dca94 100644 --- a/arch/alpha/Makefile +++ b/arch/alpha/Makefile @@ -27,10 +27,16 @@ cpuflags-$(CONFIG_ALPHA_GENERIC) :=3D -mcpu=3Dev56 -mtu= ne=3Dev6 cflags-y +=3D $(cpuflags-y) =20 =20 +KBUILD_CFLAGS +=3D $(cflags-y) + # For TSUNAMI, we must have the assembler not emulate our instructions. # The same is true for IRONGATE, POLARIS, PYXIS. # BWX is most important, but we don't really want any emulation ever. -KBUILD_CFLAGS +=3D $(cflags-y) -Wa,-mev6 +# Only gas emulates instructions the target does not implement, and only g= as +# understands -mev6. LLVM's integrated assembler never emulates. +ifdef CONFIG_AS_IS_GNU +KBUILD_CFLAGS +=3D -Wa,-mev6 +endif =20 libs-y +=3D arch/alpha/lib/ =20 --=20 2.54.0 From nobody Fri Oct 2 08:28:38 2026 Received: from mail-yw1-f180.google.com (mail-yw1-f180.google.com [209.85.128.180]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id DFE8D41A4FC for ; Mon, 3 Aug 2026 17:08:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.180 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785776928; cv=none; b=KsRjnilxRTcC80rTI7WLRVo2/O4OayavJObE/KCUW9spcecKNrQ0TTEV0wkU2EFlB75ZQxCia+USQnD9+Gku/Njr+t1wBfesXM9OjxADV6PdRXChd5y7Y3gNKQxMNf9xmKRaPEMlqawnK6fAsl8XIQNFRvKScNHEnqhDBehdfE4= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785776928; c=relaxed/simple; bh=Qrbmd/gCZNU62r1uQY3MotPz1q+A9zHKQVoWcbXVOqI=; 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a=openpgp-sha256; l=2059; i=mattst88@gmail.com; h=from:subject:message-id; bh=Qrbmd/gCZNU62r1uQY3MotPz1q+A9zHKQVoWcbXVOqI=; b=owGbwMvMwCW25rVmCc8sv+mMp9WSGLIKTkuu6PPRZIy51x96/X9GXXfd2znlU/aZKLQkChXzc B9zzFrY8ZGFQYyLYaaYIkvcekWWWW07lvqclv4FM4eVCWSItEgDAxCwMPDlJuaVGukY6ZlqG+oZ Ahk6RvEQOT0Gjczi4tLUIt20giKHvPySxJLM/LxivfyC1LyC9AK9tMy0koyM/KLiVKARenmpJaa ujm5GhgYmlo4WZk4WjqYmzs5Ohk5ujo7Ork5GluYmBs6WjiauluYMXJwCMNfYr2Jk+C8svOPN2t 7wRraza+7dM7J6Wb2/wvS0r3jnnVU7QiIa1zMyzNsQlhUdOkU04/SaLevnVV10vuDx/+uGPy77d 3kbdfFs5wIA X-Developer-Key: i=mattst88@gmail.com; a=openpgp; fpr=3BB639E56F861FA2E86505690FDD682D974CA72A Register the clang target triple for alpha, and pass -Wa,-mev6 only when building with gcc. That flag exists to stop gas emulating instructions the assembler thinks the target lacks; it is a gas-only option, and clang's integrated assembler does not emulate instructions in the first place, so nothing is needed there. With this, LLVM=3D1 (and LLVM_IAS=3D1) builds work. Note that the alpha backend is not in upstream LLVM yet; it lives in https://github.com/alphalinux-org/llvm-project and is a work in progress. Signed-off-by: Matt Turner --- arch/alpha/Makefile | 8 +++++++- scripts/Makefile.clang | 1 + 2 files changed, 8 insertions(+), 1 deletion(-) diff --git a/arch/alpha/Makefile b/arch/alpha/Makefile index 35445ff2e489..54283705911f 100644 --- a/arch/alpha/Makefile +++ b/arch/alpha/Makefile @@ -27,10 +27,16 @@ cpuflags-$(CONFIG_ALPHA_GENERIC) :=3D -mcpu=3Dev56 -mtu= ne=3Dev6 cflags-y +=3D $(cpuflags-y) =20 =20 +KBUILD_CFLAGS +=3D $(cflags-y) + # For TSUNAMI, we must have the assembler not emulate our instructions. # The same is true for IRONGATE, POLARIS, PYXIS. # BWX is most important, but we don't really want any emulation ever. -KBUILD_CFLAGS +=3D $(cflags-y) -Wa,-mev6 +# Only gas emulates instructions the target does not implement, and only g= as +# understands -mev6; clang's integrated assembler never emulates. +ifdef CONFIG_CC_IS_GCC +KBUILD_CFLAGS +=3D -Wa,-mev6 +endif =20 libs-y +=3D arch/alpha/lib/ =20 diff --git a/scripts/Makefile.clang b/scripts/Makefile.clang index b67636b28c35..2434cf90ad7e 100644 --- a/scripts/Makefile.clang +++ b/scripts/Makefile.clang @@ -1,6 +1,7 @@ # Individual arch/{arch}/Makefiles should use -EL/-EB to set intended # endianness and -m32/-m64 to set word size based on Kconfigs instead of # relying on the target triple. +CLANG_TARGET_FLAGS_alpha :=3D alpha-linux-gnu CLANG_TARGET_FLAGS_arm :=3D arm-linux-gnueabi CLANG_TARGET_FLAGS_arm64 :=3D aarch64-linux-gnu CLANG_TARGET_FLAGS_hexagon :=3D hexagon-linux-musl --=20 2.54.0 From nobody Fri Oct 2 08:28:38 2026 Received: from mail-yx1-f43.google.com (mail-yx1-f43.google.com [74.125.224.43]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3C1C341D230 for ; 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Mon, 03 Aug 2026 10:08:47 -0700 (PDT) Received: from localhost ([2600:1702:7a90:6f9f:8bc4:8aec:108d:7a04]) by smtp.gmail.com with ESMTPSA id 956f58d0204a3-66948cff660sm5919696d50.3.2026.08.03.10.08.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 03 Aug 2026 10:08:46 -0700 (PDT) From: Matt Turner Date: Mon, 03 Aug 2026 13:08:42 -0400 Subject: [PATCH 2/2] alpha: read $gp and $sp explicitly for clang Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20260803-alpha-clang-v1-2-1c4ba5ba7a64@gmail.com> References: <20260803-alpha-clang-v1-0-1c4ba5ba7a64@gmail.com> In-Reply-To: <20260803-alpha-clang-v1-0-1c4ba5ba7a64@gmail.com> To: Richard Henderson , Matt Turner , Magnus Lindholm , Nathan Chancellor , Nick Desaulniers , Bill Wendling , Justin Stitt , Nicolas Schier Cc: linux-alpha@vger.kernel.org, linux-kernel@vger.kernel.org, llvm@lists.linux.dev, linux-kbuild@vger.kernel.org X-Mailer: b4 0.14.3 X-Developer-Signature: v=1; a=openpgp-sha256; l=1672; i=mattst88@gmail.com; h=from:subject:message-id; bh=6GCvx4EVOSNKyzp+tXGGIXMLeA/q5fZSG5xq+Mpfmmc=; b=owGbwMvMwCW25rVmCc8sv+mMp9WSGLIKTkt67tDONuewvFWbu1Za5LmoqqLj5D9b13DGKfyO+ KSq6d7b8ZGFQYyLYaaYIkvcekWWWW07lvqclv4FM4eVCWSItEgDAxCwMPDlJuaVGukY6ZlqG+oZ Ahk6RvEQOT0Gjczi4tLUIt20giKHvPySxJLM/LxivfyC1LyC9AK9tMy0koyM/KLiVKARenmpJaa ujm5GhgYmlo4WZk4WjqYmzs5Ohk5ujo7Ork5GluYmBs6WjiauluYMXJwCMNeYSTIybOP2U+cLms Www/t5Scqqmx+2393s3DbZfl8e+8UFR/7XOjAyXC5vWcgXfshV58LzPHHJ7mclLo94f3HmeW1tk GD8/e0dEwA= X-Developer-Key: i=mattst88@gmail.com; a=openpgp; fpr=3BB639E56F861FA2E86505690FDD682D974CA72A clang honors a local `register unsigned long x __asm__("$N")` variable only where it appears as an inline-asm operand; merely reading it does not produce the contents of that register. So trap_init() passed an undefined global pointer to PAL_wrkgp, and load_PCB() stored an undefined stack pointer into the PCB that swpctx then loaded. Either one wedges an early boot. Read the registers explicitly instead: an inline mov for $gp in trap_init(), and the file-scope current_stack_pointer for $sp in load_PCB(). A file-scope register-asm variable is the form clang does support. Signed-off-by: Matt Turner Reviewed-by: Maciej W. Rozycki Reviewed-by: Magnus Lindholm linmag7@gmail.com Tested-by: Magnus Lindholm linmag7@gmail.com --- arch/alpha/kernel/traps.c | 4 +++- arch/alpha/mm/init.c | 3 +-- 2 files changed, 4 insertions(+), 3 deletions(-) diff --git a/arch/alpha/kernel/traps.c b/arch/alpha/kernel/traps.c index 7631129ac914..5b4f1ae2b74b 100644 --- a/arch/alpha/kernel/traps.c +++ b/arch/alpha/kernel/traps.c @@ -925,7 +925,9 @@ void trap_init(void) { /* Tell PAL-code what global pointer we want in the kernel. */ - register unsigned long gptr __asm__("$29"); + unsigned long gptr; + + __asm__ volatile("mov $29, %0" : "=3Dr"(gptr)); wrkgp(gptr); =20 wrent(entArith, 1); diff --git a/arch/alpha/mm/init.c b/arch/alpha/mm/init.c index 9531cbc761c0..f4d65a60c869 100644 --- a/arch/alpha/mm/init.c +++ b/arch/alpha/mm/init.c @@ -63,8 +63,7 @@ pgd_alloc(struct mm_struct *mm) static inline unsigned long load_PCB(struct pcb_struct *pcb) { - register unsigned long sp __asm__("$30"); - pcb->ksp =3D sp; + pcb->ksp =3D (unsigned long)current_stack_pointer; return __reload_thread(pcb); } =20 --=20 2.54.0