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/<pid>/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 <linmag7@gmail.com> Tested-by: Magnus Lindholm <linmag7@gmail.com> Acked-by: Ian Rogers <irogers@google.com> Signed-off-by: Matt Turner <mattst88@gmail.com> Link: https://lore.kernel.org/r/20261018-alpha-perf-regs-v3-v3-1-52be85332c57@gmail.com Signed-off-by: Magnus Lindholm <linmag7@gmail.com>