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[108.93.236.139]) by smtp.gmail.com with ESMTPSA id 00721157ae682-8b0e5885546sm16379857b3.16.2026.10.16.18.55.58 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 16 Oct 2026 18:56:00 -0700 (PDT) From: Matt Turner Date: Fri, 16 Oct 2026 21:55:47 -0400 Subject: [PATCH v2 1/5] 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: <20261016-alpha-perf-regs-v3-v2-1-17654742226a@gmail.com> References: <20261016-alpha-perf-regs-v3-v2-0-17654742226a@gmail.com> In-Reply-To: <20261016-alpha-perf-regs-v3-v2-0-17654742226a@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, Ian Rogers , Matt Turner X-Mailer: b4 0.14.3 X-Developer-Signature: v=1; a=openpgp-sha256; l=2375; i=mattst88@gmail.com; h=from:subject:message-id; bh=3hBEoYmujIN/lIM+LWmpcdreauHJLGhIJOlga1pFDNU=; b=owGbwMvMwCW25rVmCc8sv+mMp9WSGLIuXV18W33zl227d0zLODlNyiLth9GZ36qJfc9uvru67 dGWLZ+2POn4yMIgxsUwU0yRJW69Isusth1LfU5L/4KZw8oEMkRapIEBCFgY+HIT80qNdIz0TLUN 9QyBDB2jeIicHoNGZnFxaWqRblpBkUNefkliSWZ+XrFefkFqXkF6gV5aZlpJRkZ+UXEq0Ai9vNQ SU1dHNyNDAxNLRwszJwtHUxNnZydDJzdHR2dXJyNLcxMDZ0tHE1dLcwYuTgGYazo+MzK0yKU0pR 2aXPAhoNPn9MdCvuvP02b2qk8r+i/+5tIW9SnODH94uyZ9Wnv3S9jbNy1xAVav9y/vSs488rxTu 2m62rr1LcXsAA== 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 Reviewed-by: Magnus Lindholm Tested-by: Magnus Lindholm Acked-by: Ian Rogers 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