target/arm: Take an exception if PC is misaligned

For A64, any input to an indirect branch can cause this.

For A32, many indirect branch paths force the branch to be aligned,
but BXWritePC does not.  This includes the BX instruction but also
other interworking changes to PC.  Prior to v8, this case is UNDEFINED.
With v8, this is CONSTRAINED UNPREDICTABLE and may either raise an
exception or force align the PC.

We choose to raise an exception because we have the infrastructure,
it makes the generated code for gen_bx simpler, and it has the
possibility of catching more guest bugs.

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

1 files changed, 27 insertions, 19 deletions

diff --git a/linux-user/aarch64/cpu_loop.c b/linux-user/aarch64/cpu_loop.c
index 97e0728b67..f9f3473288 100644
--- a/linux-user/aarch64/cpu_loop.c
+++ b/linux-user/aarch64/cpu_loop.c
@@ -113,27 +113,35 @@ void cpu_loop(CPUARMState *env)
             break;
         case EXCP_PREFETCH_ABORT:
         case EXCP_DATA_ABORT:
-            /* We should only arrive here with EC in {DATAABORT, INSNABORT}. */
             ec = syn_get_ec(env->exception.syndrome);
-            assert(ec == EC_DATAABORT || ec == EC_INSNABORT);
-
-            /* Both EC have the same format for FSC, or close enough. */
-            fsc = extract32(env->exception.syndrome, 0, 6);
-            switch (fsc) {
-            case 0x04 ... 0x07: /* Translation fault, level {0-3} */
-                si_signo = TARGET_SIGSEGV;
-                si_code = TARGET_SEGV_MAPERR;
+            switch (ec) {
+            case EC_DATAABORT:
+            case EC_INSNABORT:
+                /* Both EC have the same format for FSC, or close enough. */
+                fsc = extract32(env->exception.syndrome, 0, 6);
+                switch (fsc) {
+                case 0x04 ... 0x07: /* Translation fault, level {0-3} */
+                    si_signo = TARGET_SIGSEGV;
+                    si_code = TARGET_SEGV_MAPERR;
+                    break;
+                case 0x09 ... 0x0b: /* Access flag fault, level {1-3} */
+                case 0x0d ... 0x0f: /* Permission fault, level {1-3} */
+                    si_signo = TARGET_SIGSEGV;
+                    si_code = TARGET_SEGV_ACCERR;
+                    break;
+                case 0x11: /* Synchronous Tag Check Fault */
+                    si_signo = TARGET_SIGSEGV;
+                    si_code = TARGET_SEGV_MTESERR;
+                    break;
+                case 0x21: /* Alignment fault */
+                    si_signo = TARGET_SIGBUS;
+                    si_code = TARGET_BUS_ADRALN;
+                    break;
+                default:
+                    g_assert_not_reached();
+                }
                 break;
-            case 0x09 ... 0x0b: /* Access flag fault, level {1-3} */
-            case 0x0d ... 0x0f: /* Permission fault, level {1-3} */
-                si_signo = TARGET_SIGSEGV;
-                si_code = TARGET_SEGV_ACCERR;
-                break;
-            case 0x11: /* Synchronous Tag Check Fault */
-                si_signo = TARGET_SIGSEGV;
-                si_code = TARGET_SEGV_MTESERR;
-                break;
-            case 0x21: /* Alignment fault */
+            case EC_PCALIGNMENT:
                 si_signo = TARGET_SIGBUS;
                 si_code = TARGET_BUS_ADRALN;
                 break;