Add CPUID::is_little_endian

Having a runtime endian test to verify against the build setting is
useful.

2 files changed, 35 insertions, 0 deletions

diff --git a/src/lib/utils/cpuid.cpp b/src/lib/utils/cpuid.cpp
index 3fafadab7..cb25ed09d 100644
--- a/src/lib/utils/cpuid.cpp
+++ b/src/lib/utils/cpuid.cpp
@@ -8,6 +8,7 @@
 #include <botan/cpuid.h>
 #include <botan/types.h>
 #include <botan/loadstor.h>
+#include <botan/exceptn.h>
 #include <botan/mem_ops.h>
 #include <ostream>
 
@@ -76,6 +77,7 @@ namespace Botan {
 u64bit CPUID::g_processor_flags[2] = { 0, 0 };
 size_t CPUID::g_cache_line_size = BOTAN_TARGET_CPU_DEFAULT_CACHE_LINE_SIZE;
 bool CPUID::g_initialized = false;
+bool CPUID::g_little_endian = false;
 
 namespace {
 
@@ -256,6 +258,29 @@ void CPUID::initialize()
       g_processor_flags[0] = (1 << CPUID_SSE2_BIT) | (1 << CPUID_RDTSC_BIT);
 #endif
 
+   const uint32_t endian32 = 0x01234567;
+   const uint8_t* e8 = reinterpret_cast<const uint8_t*>(&endian32);
+
+   if(e8[0] == 0x01 && e8[1] == 0x23 && e8[2] == 0x45 && e8[3] == 0x67)
+      {
+      g_little_endian = false;
+      }
+   else if(e8[0] == 0x67 && e8[1] == 0x45 && e8[2] == 0x23 && e8[3] == 0x01)
+      {
+      g_little_endian = true;
+      }
+   else
+      {
+      throw Internal_Error("Unexpected endian at runtime, neither big nor little");
+      }
+
+   // If we were compiled with a known endian, verify if matches at runtime
+#if defined(BOTAN_TARGET_CPU_IS_LITTLE_ENDIAN)
+   BOTAN_ASSERT(g_little_endian, "Little-endian build but big-endian at runtime");
+#elif defined(BOTAN_TARGET_CPU_IS_BIG_ENDIAN)
+   BOTAN_ASSERT(!g_little_endian, "Big-endian build but little-endian at runtime");
+#endif
+
    g_initialized = true;
    }
 
diff --git a/src/lib/utils/cpuid.h b/src/lib/utils/cpuid.h
index 53e59e9e5..aa7bae963 100644
--- a/src/lib/utils/cpuid.h
+++ b/src/lib/utils/cpuid.h
@@ -42,6 +42,15 @@ class BOTAN_DLL CPUID
          return g_cache_line_size;
          }
 
+      static bool is_little_endian()
+         {
+         if(!g_initialized)
+            {
+            initialize();
+            }
+         return g_little_endian;
+         }
+
       enum CPUID_bits {
 #if defined(BOTAN_TARGET_CPU_IS_X86_FAMILY)
          // This matches the layout of cpuid(1)
@@ -184,6 +193,7 @@ class BOTAN_DLL CPUID
 
    private:
       static bool g_initialized;
+      static bool g_little_endian;
       static size_t g_cache_line_size;
       static u64bit g_processor_flags[2];
    };