target/arm: Move helper_exception_return to helper-a64.c

This function is only used by AArch64.  Code movement only.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20190108223129.5570-11-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

1 files changed, 155 insertions, 0 deletions

diff --git a/target/arm/helper-a64.c b/target/arm/helper-a64.c
index 61799d20e1..66ff70dcdb 100644
--- a/target/arm/helper-a64.c
+++ b/target/arm/helper-a64.c
@@ -887,6 +887,161 @@ uint32_t HELPER(advsimd_f16touinth)(uint32_t a, void *fpstp)
     return float16_to_uint16(a, fpst);
 }
 
+static int el_from_spsr(uint32_t spsr)
+{
+    /* Return the exception level that this SPSR is requesting a return to,
+     * or -1 if it is invalid (an illegal return)
+     */
+    if (spsr & PSTATE_nRW) {
+        switch (spsr & CPSR_M) {
+        case ARM_CPU_MODE_USR:
+            return 0;
+        case ARM_CPU_MODE_HYP:
+            return 2;
+        case ARM_CPU_MODE_FIQ:
+        case ARM_CPU_MODE_IRQ:
+        case ARM_CPU_MODE_SVC:
+        case ARM_CPU_MODE_ABT:
+        case ARM_CPU_MODE_UND:
+        case ARM_CPU_MODE_SYS:
+            return 1;
+        case ARM_CPU_MODE_MON:
+            /* Returning to Mon from AArch64 is never possible,
+             * so this is an illegal return.
+             */
+        default:
+            return -1;
+        }
+    } else {
+        if (extract32(spsr, 1, 1)) {
+            /* Return with reserved M[1] bit set */
+            return -1;
+        }
+        if (extract32(spsr, 0, 4) == 1) {
+            /* return to EL0 with M[0] bit set */
+            return -1;
+        }
+        return extract32(spsr, 2, 2);
+    }
+}
+
+void HELPER(exception_return)(CPUARMState *env)
+{
+    int cur_el = arm_current_el(env);
+    unsigned int spsr_idx = aarch64_banked_spsr_index(cur_el);
+    uint32_t spsr = env->banked_spsr[spsr_idx];
+    int new_el;
+    bool return_to_aa64 = (spsr & PSTATE_nRW) == 0;
+
+    aarch64_save_sp(env, cur_el);
+
+    arm_clear_exclusive(env);
+
+    /* We must squash the PSTATE.SS bit to zero unless both of the
+     * following hold:
+     *  1. debug exceptions are currently disabled
+     *  2. singlestep will be active in the EL we return to
+     * We check 1 here and 2 after we've done the pstate/cpsr write() to
+     * transition to the EL we're going to.
+     */
+    if (arm_generate_debug_exceptions(env)) {
+        spsr &= ~PSTATE_SS;
+    }
+
+    new_el = el_from_spsr(spsr);
+    if (new_el == -1) {
+        goto illegal_return;
+    }
+    if (new_el > cur_el
+        || (new_el == 2 && !arm_feature(env, ARM_FEATURE_EL2))) {
+        /* Disallow return to an EL which is unimplemented or higher
+         * than the current one.
+         */
+        goto illegal_return;
+    }
+
+    if (new_el != 0 && arm_el_is_aa64(env, new_el) != return_to_aa64) {
+        /* Return to an EL which is configured for a different register width */
+        goto illegal_return;
+    }
+
+    if (new_el == 2 && arm_is_secure_below_el3(env)) {
+        /* Return to the non-existent secure-EL2 */
+        goto illegal_return;
+    }
+
+    if (new_el == 1 && (arm_hcr_el2_eff(env) & HCR_TGE)) {
+        goto illegal_return;
+    }
+
+    qemu_mutex_lock_iothread();
+    arm_call_pre_el_change_hook(arm_env_get_cpu(env));
+    qemu_mutex_unlock_iothread();
+
+    if (!return_to_aa64) {
+        env->aarch64 = 0;
+        /* We do a raw CPSR write because aarch64_sync_64_to_32()
+         * will sort the register banks out for us, and we've already
+         * caught all the bad-mode cases in el_from_spsr().
+         */
+        cpsr_write(env, spsr, ~0, CPSRWriteRaw);
+        if (!arm_singlestep_active(env)) {
+            env->uncached_cpsr &= ~PSTATE_SS;
+        }
+        aarch64_sync_64_to_32(env);
+
+        if (spsr & CPSR_T) {
+            env->regs[15] = env->elr_el[cur_el] & ~0x1;
+        } else {
+            env->regs[15] = env->elr_el[cur_el] & ~0x3;
+        }
+        qemu_log_mask(CPU_LOG_INT, "Exception return from AArch64 EL%d to "
+                      "AArch32 EL%d PC 0x%" PRIx32 "\n",
+                      cur_el, new_el, env->regs[15]);
+    } else {
+        env->aarch64 = 1;
+        pstate_write(env, spsr);
+        if (!arm_singlestep_active(env)) {
+            env->pstate &= ~PSTATE_SS;
+        }
+        aarch64_restore_sp(env, new_el);
+        env->pc = env->elr_el[cur_el];
+        qemu_log_mask(CPU_LOG_INT, "Exception return from AArch64 EL%d to "
+                      "AArch64 EL%d PC 0x%" PRIx64 "\n",
+                      cur_el, new_el, env->pc);
+    }
+    /*
+     * Note that cur_el can never be 0.  If new_el is 0, then
+     * el0_a64 is return_to_aa64, else el0_a64 is ignored.
+     */
+    aarch64_sve_change_el(env, cur_el, new_el, return_to_aa64);
+
+    qemu_mutex_lock_iothread();
+    arm_call_el_change_hook(arm_env_get_cpu(env));
+    qemu_mutex_unlock_iothread();
+
+    return;
+
+illegal_return:
+    /* Illegal return events of various kinds have architecturally
+     * mandated behaviour:
+     * restore NZCV and DAIF from SPSR_ELx
+     * set PSTATE.IL
+     * restore PC from ELR_ELx
+     * no change to exception level, execution state or stack pointer
+     */
+    env->pstate |= PSTATE_IL;
+    env->pc = env->elr_el[cur_el];
+    spsr &= PSTATE_NZCV | PSTATE_DAIF;
+    spsr |= pstate_read(env) & ~(PSTATE_NZCV | PSTATE_DAIF);
+    pstate_write(env, spsr);
+    if (!arm_singlestep_active(env)) {
+        env->pstate &= ~PSTATE_SS;
+    }
+    qemu_log_mask(LOG_GUEST_ERROR, "Illegal exception return at EL%d: "
+                  "resuming execution at 0x%" PRIx64 "\n", cur_el, env->pc);
+}
+
 /*
  * Square Root and Reciprocal square root
  */