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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 $sp explicitly for clang Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20260803-alpha-clang-v1-2-1c4ba5ba7a64@gmail.com> References: <20260803-alpha-clang-v1-0-1c4ba5ba7a64@gmail.com> In-Reply-To: <20260803-alpha-clang-v1-0-1c4ba5ba7a64@gmail.com> To: Richard Henderson , Matt Turner , Magnus Lindholm , Nathan Chancellor , Nick Desaulniers , Bill Wendling , Justin Stitt , Nicolas Schier Cc: linux-alpha@vger.kernel.org, linux-kernel@vger.kernel.org, llvm@lists.linux.dev, linux-kbuild@vger.kernel.org X-Mailer: b4 0.14.3 X-Developer-Signature: v=1; a=openpgp-sha256; l=1672; i=mattst88@gmail.com; h=from:subject:message-id; bh=6GCvx4EVOSNKyzp+tXGGIXMLeA/q5fZSG5xq+Mpfmmc=; b=owGbwMvMwCW25rVmCc8sv+mMp9WSGLIKTkt67tDONuewvFWbu1Za5LmoqqLj5D9b13DGKfyO+ KSq6d7b8ZGFQYyLYaaYIkvcekWWWW07lvqclv4FM4eVCWSItEgDAxCwMPDlJuaVGukY6ZlqG+oZ Ahk6RvEQOT0Gjczi4tLUIt20giKHvPySxJLM/LxivfyC1LyC9AK9tMy0koyM/KLiVKARenmpJaa ujm5GhgYmlo4WZk4WjqYmzs5Ohk5ujo7Ork5GluYmBs6WjiauluYMXJwCMNeYSTIybOP2U+cLms Www/t5Scqqmx+2393s3DbZfl8e+8UFR/7XOjAyXC5vWcgXfshV58LzPHHJ7mclLo94f3HmeW1tk GD8/e0dEwA= X-Developer-Key: i=mattst88@gmail.com; a=openpgp; fpr=3BB639E56F861FA2E86505690FDD682D974CA72A clang honors a local `register unsigned long x __asm__("$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 --- 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" : "=r"(gptr)); wrkgp(gptr); 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 = sp; + pcb->ksp = (unsigned long)current_stack_pointer; return __reload_thread(pcb); } -- 2.54.0