arch: Add a virtual asBytes function to the StaticInst class.

This function takes a pointer to a buffer and the current size of the
buffer as a pass by reference argument. If the size of the buffer is
sufficient, the function stores a binary representation of itself
(generally the ISA defined instruction encoding) in the buffer, and
sets the size argument to how much space it used. This could be used
by ISAs which have two instruction sizes (ARM and thumb, for example).
If the buffer size isn't sufficient, then the size parameter should be
set to what size is required, and then the function should return
without modifying the buffer.

The buffer itself should be aligned to the same standard as memory
returned by new, specifically "The pointer returned shall be suitably
aligned so that it can be converted to a pointer of any complete object
type and then used to access the object or array in the storage
allocated...". This will avoid having to memcpy buffers to avoid
unaligned accesses.

To standardize the representation of the data, it should be stored in
the buffer as little endian. Since most hosts (including ARM and x86
hosts) will be little endian, this will almost always be a no-op.

Change-Id: I2f31aa0b4f9c0126b44f47a881c2901243279bd6
Reviewed-on: https://gem5-review.googlesource.com/7562
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Gabe Black <gabeblack@google.com>

1 files changed, 27 insertions, 0 deletions

diff --git a/src/cpu/static_inst.hh b/src/cpu/static_inst.hh
index 79f45d828..84b352502 100644
--- a/src/cpu/static_inst.hh
+++ b/src/cpu/static_inst.hh
@@ -33,6 +33,7 @@
 #define __CPU_STATIC_INST_HH__
 
 #include <bitset>
+#include <memory>
 #include <string>
 
 #include "arch/registers.hh"
@@ -47,6 +48,7 @@
 #include "cpu/static_inst_fwd.hh"
 #include "cpu/thread_context.hh"
 #include "enums/StaticInstFlags.hh"
+#include "sim/byteswap.hh"
 
 // forward declarations
 class Packet;
@@ -317,6 +319,31 @@ class StaticInst : public RefCounted, public StaticInstFlags
 
     /// Return name of machine instruction
     std::string getName() { return mnemonic; }
+
+  protected:
+    template<typename T>
+    size_t
+    simpleAsBytes(void *buf, size_t max_size, const T &t)
+    {
+        size_t size = sizeof(T);
+        if (size <= max_size)
+            *reinterpret_cast<T *>(buf) = htole<T>(t);
+        return size;
+    }
+
+  public:
+    /**
+     * Instruction classes can override this function to return a
+     * a representation of themselves as a blob of bytes, generally assumed to
+     * be that instructions ExtMachInst.
+     *
+     * buf is a buffer to hold the bytes.
+     * max_size is the size allocated for that buffer by the caller.
+     * The return value is how much data was actually put into the buffer,
+     * zero if no data was put in the buffer, or the necessary size of the
+     * buffer if there wasn't enough space.
+     */
+    virtual size_t asBytes(void *buf, size_t max_size) { return 0; }
 };
 
 #endif // __CPU_STATIC_INST_HH__