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Sun, 11 Oct 2026 13:16:46 -0700 (PDT) From: Matt Turner Date: Sun, 11 Oct 2026 16:16:41 -0400 Subject: [PATCH 1/4] alpha: fix stale user_stack_pointer() 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: <20261011-alpha-perf-regs-v3-v1-1-eaa625a39712@gmail.com> References: <20261011-alpha-perf-regs-v3-v1-0-eaa625a39712@gmail.com> In-Reply-To: <20261011-alpha-perf-regs-v3-v1-0-eaa625a39712@gmail.com> To: Richard Henderson , Magnus Lindholm Cc: linux-alpha@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-perf-users@vger.kernel.org, Matt Turner X-Mailer: b4 0.14.3 X-Developer-Signature: v=1; a=openpgp-sha256; l=2234; i=mattst88@gmail.com; h=from:subject:message-id; bh=yxtUD1Wg31N+ed74uTZEXH2iw92qBPZ4dDNqgAridNs=; b=owGbwMvMwCW25rVmCc8sv+mMp9WSGLJOv1sVuKtp8QYjqRt37D9ZF30RPfuHOfm5752Jhg4yj fZ7XrHIdnxkYRDjYpgppsgSt16RZVbbjqU+p6V/wcxhZQIZIi3SwAAELAx8uYl5pUY6Rnqm2oZ6 hkCGjlE8RE6PQSOzuLg0tUg3raDIIS+/JLEkMz+vWC+/IDWvIL1ALy0zrSQjI7+oOBVohF5eaom pq6ObkaGBiaWjhZmThaOpibOzk6GTm6Ojs6uTkaW5iYGzpaOJq6U5AxenAMw1pwsYGa7t2r2NLf xxwY1n3h9OGLz3+fuGgyF08f+VZ/98u+/Ec+kTI0OHsd7njsxU4drKZ5NSt/iuOWulIfzjnAH7L yXlr/KnehgA X-Developer-Key: i=mattst88@gmail.com; a=openpgp; fpr=3BB639E56F861FA2E86505690FDD682D974CA72A PALcode keeps the user stack pointer in the PCB, not the trap frame, so pt_regs->usp is only valid where entry code stores it: entSys, do_entArith() and do_entIF(). Interrupts, page faults and unaligned traps leave it stale, and ptrace and /proc//syscall read it through user_stack_pointer(). A user-mode pt_regs is at the top of its task's stack, so find the thread_info from it and use rdusp() for current or pcb.usp otherwise, as KSTK_ESP() and the regset code already do. Fixes: 8a2857bc2b30 ("alpha: enable regset-based ptrace and core dumps") Assisted-by: Claude:claude-opus-5-5 Signed-off-by: Matt Turner --- arch/alpha/include/asm/ptrace.h | 7 +------ arch/alpha/kernel/ptrace.c | 12 ++++++++++++ 2 files changed, 13 insertions(+), 6 deletions(-) diff --git a/arch/alpha/include/asm/ptrace.h b/arch/alpha/include/asm/ptrace.h index 430e8dc27ff7..45d1229344b6 100644 --- a/arch/alpha/include/asm/ptrace.h +++ b/arch/alpha/include/asm/ptrace.h @@ -26,12 +26,7 @@ static inline unsigned long regs_return_value(struct pt_regs *regs) return regs->r0; } -/* Helpers for working with the user stack pointer */ -static inline unsigned long user_stack_pointer(struct pt_regs *regs) -{ - /* Valid for user-mode regs */ - return regs->usp; -} +unsigned long user_stack_pointer(struct pt_regs *regs); static __always_inline bool regs_irqs_disabled(struct pt_regs *regs) { diff --git a/arch/alpha/kernel/ptrace.c b/arch/alpha/kernel/ptrace.c index e1d8c2f69688..dba7e9905cfa 100644 --- a/arch/alpha/kernel/ptrace.c +++ b/arch/alpha/kernel/ptrace.c @@ -440,6 +440,18 @@ ptrace_cancel_bpt(struct task_struct * child) return (nsaved != 0); } +/* + * PALcode keeps the user stack pointer in the PCB, not the trap frame. + * A user-mode pt_regs sits at the top of its task's stack, so the + * thread_info is at the base. + */ +unsigned long user_stack_pointer(struct pt_regs *regs) +{ + struct thread_info *ti = (void *)((unsigned long)regs & -THREAD_SIZE); + + return ti == current_thread_info() ? rdusp() : ti->pcb.usp; +} + void user_enable_single_step(struct task_struct *child) { /* Mark single stepping. */ -- 2.55.0