From ac27ac75ac9dc091b8a10c1124b55c0c66b89258 Mon Sep 17 00:00:00 2001
From: vxiiduu <73044267+vxiiduu@users.noreply.github.com>
Date: Sat, 12 Aug 2023 22:19:16 +1000
Subject: [PATCH] Enhance Windows 7 compatibility.

---
 llama-util.h | 29 ++++++++++++++++++++++-------
 1 file changed, 22 insertions(+), 7 deletions(-)

diff --git a/llama-util.h b/llama-util.h
index 6e9e39ddb..0c967e100 100644
--- a/llama-util.h
+++ b/llama-util.h
@@ -273,13 +273,28 @@ struct llama_mmap {
 
         #if _WIN32_WINNT >= _WIN32_WINNT_WIN8
         if (prefetch) {
-            // Advise the kernel to preload the mapped memory
-            WIN32_MEMORY_RANGE_ENTRY range;
-            range.VirtualAddress = addr;
-            range.NumberOfBytes = (SIZE_T)size;
-            if (!PrefetchVirtualMemory(GetCurrentProcess(), 1, &range, 0)) {
-                fprintf(stderr, "warning: PrefetchVirtualMemory failed: %s\n",
-                        llama_format_win_err(GetLastError()).c_str());
+            // The PrefetchVirtualMemory API is only present on Windows 8 and above, so we
+            // will dynamically load it using GetProcAddress.
+            BOOL (WINAPI *pPrefetchVirtualMemory) (HANDLE, ULONG_PTR, PWIN32_MEMORY_RANGE_ENTRY, ULONG);
+            HMODULE hKernel32;
+
+            // This call is guaranteed to succeed.
+            hKernel32 = GetModuleHandleW(L"kernel32.dll");
+
+            // This call may fail if on a pre-Win8 system.
+            pPrefetchVirtualMemory = 
+                (BOOL (WINAPI *) (HANDLE, ULONG_PTR, PWIN32_MEMORY_RANGE_ENTRY, ULONG))
+                GetProcAddress(hKernel32, "PrefetchVirtualMemory");
+
+            if (pPrefetchVirtualMemory) {
+                // Advise the kernel to preload the mapped memory.
+                WIN32_MEMORY_RANGE_ENTRY range;
+                range.VirtualAddress = addr;
+                range.NumberOfBytes = (SIZE_T)size;
+                if (!pPrefetchVirtualMemory(GetCurrentProcess(), 1, &range, 0)) {
+                    fprintf(stderr, "warning: PrefetchVirtualMemory failed: %s\n",
+                            llama_format_win_err(GetLastError()).c_str());
+                }
             }
         }
         #else