Final cygwin support updates

Author: jeremy-rifkin

src/from_current.cpp

@@ -294,7 +294,7 @@ namespace detail {
         if(type_info_addr - page_addr + sizeof(void*) > static_cast<unsigned>(page_size)) {
             throw internal_error("pointer crosses page boundaries");
         }
-        #if IS_WINDOWS
+        #if IS_WINDOWS || defined(__CYGWIN__)
         auto old_protections = mprotect_page_and_return_old_protections(
             reinterpret_cast<void*>(page_addr),
             page_size,

src/platform/memory_mapping.cpp

@@ -5,7 +5,7 @@
 
 #ifndef _MSC_VER
 
-#if IS_WINDOWS
+#if IS_WINDOWS || defined(__CYGWIN__)
  #ifndef WIN32_LEAN_AND_MEAN
   #define WIN32_LEAN_AND_MEAN
  #endif
@@ -31,7 +31,10 @@
 
 CPPTRACE_BEGIN_NAMESPACE
 namespace detail {
-    #if IS_WINDOWS
+    #if IS_WINDOWS || defined(__CYGWIN__)
+    // Cygwin uses GCC/Itanium ABI but Cygwin's mprotect seems to require 64KB-aligned addresses (allocation
+    // granularity returned by sysconf(_SC_PAGESIZE)) while we need actual page granularity for typeinfo surgery.
+    // Using the windows API here works best.
     int get_page_size() {
         SYSTEM_INFO info;
         GetSystemInfo(&info);

src/platform/memory_mapping.hpp

@@ -2,7 +2,7 @@
 
 #ifndef _MSC_VER
 
-#if IS_WINDOWS
+#if IS_WINDOWS || defined(__CYGWIN__)
  #ifndef WIN32_LEAN_AND_MEAN
   #define WIN32_LEAN_AND_MEAN
  #endif
@@ -13,15 +13,15 @@
 
 CPPTRACE_BEGIN_NAMESPACE
 namespace detail {
-    #if IS_WINDOWS
+    #if IS_WINDOWS || defined(__CYGWIN__)
      constexpr auto memory_readonly = PAGE_READONLY;
      constexpr auto memory_readwrite = PAGE_READWRITE;
     #else
      constexpr auto memory_readonly = PROT_READ;
      constexpr auto memory_readwrite = PROT_READ | PROT_WRITE;
     #endif
     int get_page_size();
-    #if !IS_WINDOWS
+    #if !IS_WINDOWS && !defined(__CYGWIN__)
      int get_page_protections(void* page);
     #endif
     int mprotect_page_and_return_old_protections(void* page, int page_size, int protections);