target-arm: Clean up trap/undef handling of SRS

The SRS instruction is:
 * UNDEFINED in Hyp mode
 * UNPREDICTABLE in User or System mode
 * UNPREDICTABLE if the specified mode isn't accessible
 * trapped to EL3 if EL3 is AArch64 and we are at Secure EL1

Clean up the code to handle all these cases cleanly, including
picking UNDEF as our choice of UNPREDICTABLE behaviour rather
blindly trusting the mode field passed in the instruction.
As part of this, move the check for IS_USER into gen_srs()
itself rather than having it done by the caller.

The exception is that we don't UNDEF for calls from System
mode, which need a runtime check. This will be dealt with in
the following commits.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Sergey Fedorov <serge.fdrv@gmail.com>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>

1 files changed, 61 insertions, 5 deletions

diff --git a/target-arm/translate.c b/target-arm/translate.c
index cf3dc33..7bceb05 100644
--- a/target-arm/translate.c
+++ b/target-arm/translate.c
@@ -7578,8 +7578,67 @@ static void gen_srs(DisasContext *s,
                     uint32_t mode, uint32_t amode, bool writeback)
 {
     int32_t offset;
-    TCGv_i32 addr = tcg_temp_new_i32();
-    TCGv_i32 tmp = tcg_const_i32(mode);
+    TCGv_i32 addr, tmp;
+    bool undef = false;
+
+    /* SRS is:
+     * - trapped to EL3 if EL3 is AArch64 and we are at Secure EL1
+     * - UNDEFINED in Hyp mode
+     * - UNPREDICTABLE in User or System mode
+     * - UNPREDICTABLE if the specified mode is:
+     * -- not implemented
+     * -- not a valid mode number
+     * -- a mode that's at a higher exception level
+     * -- Monitor, if we are Non-secure
+     * For the UNPREDICTABLE cases we choose to UNDEF, except that for
+     * "current mode is System" we will write a garbage SPSR.
+     * (This is because we don't have access to our current mode here
+     * and would have to do a runtime check to UNDEF for System.)
+     */
+    if (s->current_el == 1 && !s->ns) {
+        gen_exception_insn(s, 4, EXCP_UDEF, syn_uncategorized(), 3);
+        return;
+    }
+
+    if (s->current_el == 0 || s->current_el == 2) {
+        undef = true;
+    }
+
+    switch (mode) {
+    case ARM_CPU_MODE_USR:
+    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:
+        break;
+    case ARM_CPU_MODE_HYP:
+        if (s->current_el == 1 || !arm_dc_feature(s, ARM_FEATURE_EL2)) {
+            undef = true;
+        }
+        break;
+    case ARM_CPU_MODE_MON:
+        /* No need to check specifically for "are we non-secure" because
+         * we've already made EL0 UNDEF and handled the trap for S-EL1;
+         * so if this isn't EL3 then we must be non-secure.
+         */
+        if (s->current_el != 3) {
+            undef = true;
+        }
+        break;
+    default:
+        undef = true;
+    }
+
+    if (undef) {
+        gen_exception_insn(s, 4, EXCP_UDEF, syn_uncategorized(),
+                           default_exception_el(s));
+        return;
+    }
+
+    addr = tcg_temp_new_i32();
+    tmp = tcg_const_i32(mode);
     gen_helper_get_r13_banked(addr, cpu_env, tmp);
     tcg_temp_free_i32(tmp);
     switch (amode) {
@@ -7739,9 +7798,6 @@ static void disas_arm_insn(DisasContext *s, unsigned int insn)
             }
         } else if ((insn & 0x0e5fffe0) == 0x084d0500) {
             /* srs */
-            if (IS_USER(s)) {
-                goto illegal_op;
-            }
             ARCH(6);
             gen_srs(s, (insn & 0x1f), (insn >> 23) & 3, insn & (1 << 21));
             return;