linux-user/aarch64: Reset PSTATE.SM on syscalls

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20220708151540.18136-35-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

linux-user/aarch64/cpu_loop.c

@@ -89,6 +89,15 @@ void cpu_loop(CPUARMState *env)
 
         switch (trapnr) {
         case EXCP_SWI:
+            /*
+             * On syscall, PSTATE.ZA is preserved, along with the ZA matrix.
+             * PSTATE.SM is cleared, per SMSTOP, which does ResetSVEState.
+             */
+            if (FIELD_EX64(env->svcr, SVCR, SM)) {
+                env->svcr = FIELD_DP64(env->svcr, SVCR, SM, 0);
+                arm_rebuild_hflags(env);
+                arm_reset_sve_state(env);
+            }
             ret = do_syscall(env,
                              env->xregs[8],
                              env->xregs[0],