emulator/opengl/emugen: Use templates to read values from stream.

The decoder didn't properly handle GLsizeiptr and GLintptr values, which
are always 32-bit on the wire, but can be 64-bit on the host. I.e. it
did something like that to read them from the stream:

  *(GLsizeiptr*)(ptr + offset)

This fixes the issue by using templates to generate host-type-specific
functions that properly read data from the stream and convert it to the
appropriate host type.

Change-Id: I75749bd715456ca143eb1713498f7cf635918801

1 files changed, 107 insertions, 0 deletions

diff --git a/emulator/opengl/shared/OpenglCodecCommon/ProtocolUtils.h b/emulator/opengl/shared/OpenglCodecCommon/ProtocolUtils.h
new file mode 100644
index 0000000..1198bd1
--- /dev/null
+++ b/emulator/opengl/shared/OpenglCodecCommon/ProtocolUtils.h
@@ -0,0 +1,107 @@
+#ifndef EMUGL_PROTOCOL_UTILS_H
+#define EMUGL_PROTOCOL_UTILS_H
+
+#include <stddef.h>
+#include <stdint.h>
+
+namespace emugl {
+
+// Helper macro
+#define COMPILE_ASSERT(cond)  static char kAssert##__LINE__[1 - 2 * !(cond)] __attribute__((unused)) = { 0 }
+
+// Helper template: is_pointer.
+// is_pointer<T>::value is true iff |T| is a pointer type.
+template <typename T> struct is_pointer {
+    static const bool value = false;
+};
+
+template <typename T> struct is_pointer<T*> {
+    static const bool value = true;
+};
+
+// A helper template to extract values form the wire protocol stream
+// and convert them to appropriate host values.
+//
+// The wire protocol uses 32-bit exclusively when transferring
+// GLintptr or GLsizei values, as well as opaque handles like GLeglImage,
+// from the guest (even when the guest is 64-bit).
+//
+// The corresponding host definitions depend on the host bitness. For
+// example, GLintptr is 64-bit on linux-x86_64. The following is a set
+// of templates that can simplify the conversion of protocol values
+// into host ones.
+//
+// The most important one is:
+//
+//     unpack<HOST_TYPE,SIZE_TYPE>(const void* ptr)
+//
+// Which reads bytes from |ptr|, using |SIZE_TYPE| as the underlying
+// sized-integer specifier (e.g. 'uint32_t'), and converting the result
+// into a |HOST_TYPE| value. For example:
+//
+//     unpack<EGLImage,uint32_t>(ptr + 12);
+//
+// will read a 4-byte value from |ptr + 12| and convert it into
+// an EGLImage, which is a host void*. The template detects host
+// pointer types to perform proper type casting.
+//
+// TODO(digit): Add custom unpackers to handle generic opaque void* values.
+//              and map them to unique 32-bit values.
+
+template <typename T, typename S, bool IS_POINTER>
+struct UnpackerT {};
+
+template <typename T, typename S>
+struct UnpackerT<T,S,false> {
+    static inline T unpack(const void* ptr) {
+        COMPILE_ASSERT(sizeof(T) == sizeof(S));
+        return (T)(*(S*)(ptr));
+    }
+};
+
+template <typename T, typename S>
+struct UnpackerT<T,S,true> {
+    static inline T unpack(const void* ptr) {
+        return (T)(uintptr_t)(*(S*)(ptr));
+    }
+};
+
+template <>
+struct UnpackerT<float,uint32_t,false> {
+    static inline float unpack(const void* ptr) {
+        union {
+            float f;
+            uint32_t u;
+        } v;
+        v.u = *(uint32_t*)(ptr);
+        return v.f;
+    }
+};
+
+template <>
+struct UnpackerT<double,uint64_t,false> {
+    static inline double unpack(const void* ptr) {
+        union {
+            double d;
+            uint32_t u;
+        } v;
+        v.u = *(uint64_t*)(ptr);
+        return v.d;
+    }
+};
+
+template <>
+struct UnpackerT<ssize_t,uint32_t,false> {
+    static inline ssize_t unpack(const void* ptr) {
+        return (ssize_t)*(int32_t*)(ptr);
+    }
+};
+
+template <typename T, typename S>
+inline T Unpack(const void* ptr) {
+    return UnpackerT<T, S, is_pointer<T>::value>::unpack(ptr);
+}
+
+}  // namespace emugl
+
+#endif  // EMUGL_PROTOCOL_UTILS_H