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, 13 insertions, 1 deletions

diff --git a/target-arm/cpu.h b/target-arm/cpu.h
index afb60ee..401955f 100644
--- a/target-arm/cpu.h
+++ b/target-arm/cpu.h
@@ -93,7 +93,19 @@
 #define ARM_CPU_VFIQ 3
 
 #define NB_MMU_MODES 7
-#define TARGET_INSN_START_EXTRA_WORDS 1
+/* ARM-specific extra insn start words:
+ * 1: Conditional execution bits
+ * 2: Partial exception syndrome for data aborts
+ */
+#define TARGET_INSN_START_EXTRA_WORDS 2
+
+/* The 2nd extra word holding syndrome info for data aborts does not use
+ * the upper 6 bits nor the lower 14 bits. We mask and shift it down to
+ * help the sleb128 encoder do a better job.
+ * When restoring the CPU state, we shift it back up.
+ */
+#define ARM_INSN_START_WORD2_MASK ((1 << 26) - 1)
+#define ARM_INSN_START_WORD2_SHIFT 14
 
 /* We currently assume float and double are IEEE single and double
    precision respectively.