arch-arm: Add aarch64 semihosting support

Add basic support for Arm Semihosting 2.0 simulation calls [1]. These
calls let the guest system call a simulator or debugger to request
OS-like support when running bare metal code.

With the exception of SYS_SYSTEM, this implementation supports all of
the Semihosting 2.0 specification in aarch64.

[1] https://developer.arm.com/docs/100863/latest/preface

Change-Id: I08c153c18a4a4fb9f95d318e2a029724935192a7
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Jack Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/8147
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>

1 files changed, 20 insertions, 1 deletions

diff --git a/src/arch/arm/system.hh b/src/arch/arm/system.hh
index 46103f42c..e7696a4fd 100644
--- a/src/arch/arm/system.hh
+++ b/src/arch/arm/system.hh
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2010, 2012-2013, 2015-2017 ARM Limited
+ * Copyright (c) 2010, 2012-2013, 2015-2018 ARM Limited
  * All rights reserved
  *
  * The license below extends only to copyright in the software and shall
@@ -122,6 +122,11 @@ class ArmSystem : public System
      */
     const AddrRange _m5opRange;
 
+    /**
+     * True if the Semihosting interface is enabled.
+     */
+    ArmSemihosting *const semihosting;
+
   protected:
     /**
      * Get a boot loader that matches the kernel.
@@ -228,6 +233,9 @@ class ArmSystem : public System
      */
     const AddrRange &m5opRange() const { return _m5opRange; }
 
+    /** Is Arm Semihosting support enabled? */
+    bool haveSemihosting() const { return semihosting != nullptr; }
+
     /**
      * Returns a valid ArmSystem pointer if using ARM ISA, it fails
      * otherwise.
@@ -280,6 +288,17 @@ class ArmSystem : public System
     /** Returns true if ASID is 16 bits for the system of a specific thread
      * context while in AArch64 (ARMv8) */
     static bool haveLargeAsid64(ThreadContext *tc);
+
+    /** Is Arm Semihosting support enabled? */
+    static bool haveSemihosting(ThreadContext *tc);
+
+    /** Make a Semihosting call from aarch64 */
+    static uint64_t callSemihosting64(ThreadContext *tc,
+                                      uint32_t op, uint64_t param);
+
+    /** Make a Semihosting call from aarch32 */
+    static uint32_t callSemihosting32(ThreadContext *tc,
+                                      uint32_t op, uint32_t param);
 };
 
 class GenericArmSystem : public ArmSystem