target-arm: A64: Create Instruction Syndromes for Data Aborts

Add support for generating the ISS (Instruction Specific Syndrome) for
Data Abort exceptions taken from AArch64.
These syndromes are used by hypervisors for example to trap and emulate
memory accesses.

We save the decoded data out-of-band with the TBs at translation time.
When exceptions hit, the extra data attached to the TB is used to
recreate the state needed to encode instruction syndromes.
This avoids the need to emit moves with every load/store.

Based on a suggestion from Peter Maydell.

Suggested-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Message-id: 1462464601-10888-2-git-send-email-edgar.iglesias@gmail.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

1 files changed, 43 insertions, 6 deletions

diff --git a/target-arm/op_helper.c b/target-arm/op_helper.c
index 0b29b9dbf2..35912a1192 100644
--- a/target-arm/op_helper.c
+++ b/target-arm/op_helper.c
@@ -76,6 +76,43 @@ uint32_t HELPER(neon_tbl)(CPUARMState *env, uint32_t ireg, uint32_t def,
 
 #if !defined(CONFIG_USER_ONLY)
 
+static inline uint32_t merge_syn_data_abort(uint32_t template_syn,
+                                            unsigned int target_el,
+                                            bool same_el,
+                                            bool s1ptw, int is_write,
+                                            int fsc)
+{
+    uint32_t syn;
+
+    /* ISV is only set for data aborts routed to EL2 and
+     * never for stage-1 page table walks faulting on stage 2.
+     *
+     * Furthermore, ISV is only set for certain kinds of load/stores.
+     * If the template syndrome does not have ISV set, we should leave
+     * it cleared.
+     *
+     * See ARMv8 specs, D7-1974:
+     * ISS encoding for an exception from a Data Abort, the
+     * ISV field.
+     */
+    if (!(template_syn & ARM_EL_ISV) || target_el != 2 || s1ptw) {
+        syn = syn_data_abort_no_iss(same_el,
+                                    0, 0, s1ptw, is_write == 1, fsc);
+    } else {
+        /* Fields: IL, ISV, SAS, SSE, SRT, SF and AR come from the template
+         * syndrome created at translation time.
+         * Now we create the runtime syndrome with the remaining fields.
+         */
+        syn = syn_data_abort_with_iss(same_el,
+                                      0, 0, 0, 0, 0,
+                                      0, 0, s1ptw, is_write == 1, fsc,
+                                      false);
+        /* Merge the runtime syndrome with the template syndrome.  */
+        syn |= template_syn;
+    }
+    return syn;
+}
+
 /* try to fill the TLB and return an exception if error. If retaddr is
  * NULL, it means that the function was called in C code (i.e. not
  * from generated code or from helper.c)
@@ -116,8 +153,8 @@ void tlb_fill(CPUState *cs, target_ulong addr, int is_write, int mmu_idx,
             syn = syn_insn_abort(same_el, 0, fi.s1ptw, syn);
             exc = EXCP_PREFETCH_ABORT;
         } else {
-            syn = syn_data_abort_no_iss(same_el,
-                                        0, 0, fi.s1ptw, is_write == 1, syn);
+            syn = merge_syn_data_abort(env->exception.syndrome, target_el,
+                                       same_el, fi.s1ptw, is_write, syn);
             if (is_write == 1 && arm_feature(env, ARM_FEATURE_V6)) {
                 fsr |= (1 << 11);
             }
@@ -138,6 +175,7 @@ void arm_cpu_do_unaligned_access(CPUState *cs, vaddr vaddr, int is_write,
     CPUARMState *env = &cpu->env;
     int target_el;
     bool same_el;
+    uint32_t syn;
 
     if (retaddr) {
         /* now we have a real cpu fault */
@@ -162,10 +200,9 @@ void arm_cpu_do_unaligned_access(CPUState *cs, vaddr vaddr, int is_write,
         env->exception.fsr |= (1 << 11);
     }
 
-    raise_exception(env, EXCP_DATA_ABORT,
-                    syn_data_abort_no_iss(same_el,
-                                          0, 0, 0, is_write == 1, 0x21),
-                    target_el);
+    syn = merge_syn_data_abort(env->exception.syndrome, target_el,
+                               same_el, 0, is_write, 0x21);
+    raise_exception(env, EXCP_DATA_ABORT, syn, target_el);
 }
 
 #endif /* !defined(CONFIG_USER_ONLY) */