git: add ARM64 runtime detection

In order to support native Git for Windows ARM64 binaries,
this commit introduces ARM64 runtime detection. Git-wrapper itself will
remain an i686 or x86_64 executable for now, but since Windows on ARM
has built-in i686 emulation, it can run the file.

If an ARM64 system is detected, we set MSYSTEM=ARM64. Next to that,
because many binaries like curl aren't available natively for ARM64 yet,
we add /mingw32/bin to the path, so that we'll fallback to i686
executables in that case.

Signed-off-by: Tommy Vercetti <7903172+tommyvct@users.noreply.github.com>
Signed-off-by: Dennis Ameling <dennis@dennisameling.com>

mingw-w64-git/PKGBUILD

@@ -62,7 +62,7 @@ sha256sums=('SKIP'
             '62f455747f33953a723ff7b070d43f0ed03c1d8d0749d7bb06288e14d356b637'
             'f16b345aba17acd124ab5940635dfa2d87445df73eedbeb80e0285f29c85415a'
             '80b0b11efe5a2f9b4cd92f28c260d0b3aad8b809c34ed95237c59b73e08ade0b'
-            '6696add21808e35ac171567e0286867ca9da8722c853af1295268869db84a602'
+            'fc99081d915161e9b7a4353bf7f0439782e000d966557852d256e3f9c67e6444'
             'ee0ed30b2601413a6efcd15f236747404cd2d576dcfad77fb5b1700852cde857'
             'c975292adae1f2666f07f8ee9b7d50576da249d9151c6bd211602adc8d37b6ab'
             'a7e80489af33468e67a39d4c9c2fbf396e1f1e9533bb447f26432951ccf5e77c'

mingw-w64-git/git-wrapper.c

@@ -13,6 +13,7 @@
 #include <shellapi.h>
 #include <stdio.h>
 #include <wchar.h>
+#include <stdbool.h>
 
 /* Let the system deal with it if the path is too long */
 #undef MAX_PATH
@@ -113,15 +114,35 @@ static void my_path_append(LPWSTR list, LPCWSTR path, size_t alloc)
 	}
 }
 
+bool IsRunningOnARM64()
+{
+	USHORT process_machine = 0;
+	USHORT native_machine = 0;
+
+	// Note: IsWow64Process2 is only available in Windows 10 1511+
+	BOOL (WINAPI* IsWow64Process2)(HANDLE, PUSHORT, PUSHORT) =
+    GetProcAddress(GetModuleHandle(L"kernel32"), "IsWow64Process2");
+
+	return IsWow64Process2 &&
+		IsWow64Process2(GetCurrentProcess(), &process_machine, &native_machine) &&
+		native_machine == 0xaa64;
+}
+
 static void setup_environment(LPWSTR top_level_path, int full_path)
 {
 	WCHAR msystem[64];
 	LPWSTR path2 = NULL;
 	int len;
 
 	/* Set MSYSTEM */
-	swprintf(msystem, sizeof(msystem),
-		L"MINGW%d", (int) sizeof(void *) * 8);
+	if (IsRunningOnARM64()) {
+		swprintf(msystem, sizeof(msystem),
+				L"ARM64");
+	} else {
+		swprintf(msystem, sizeof(msystem),
+				L"MINGW%d", (int)sizeof(void*) * 8);
+	}
+
 	SetEnvironmentVariable(L"MSYSTEM", msystem);
 
 	/* if not set, set PLINK_PROTOCOL to ssh */
@@ -164,13 +185,22 @@ static void setup_environment(LPWSTR top_level_path, int full_path)
 
 	/* extend the PATH */
 	len = GetEnvironmentVariable(L"PATH", NULL, 0);
-	len = sizeof(WCHAR) * (len + 3 * MAX_PATH);
+	len = sizeof(WCHAR) * (len + 4 * MAX_PATH);
 	path2 = (LPWSTR)malloc(len);
 	wcscpy(path2, top_level_path);
 	if (!full_path)
 		my_path_append(path2, L"cmd;", len);
 	else {
 		my_path_append(path2, msystem_bin, len);
+		if (IsRunningOnARM64()) {
+			/*
+			 * Many modules aren't available natively for ARM64 yet, but we can leverage i686 emulation.
+			 * Therefore we add /minw32/bin to the path.
+			 */
+			wcscat(path2, L";");
+			wcscat(path2, top_level_path);
+			my_path_append(path2, L"mingw32\\bin;", len);
+		}
 		if (_waccess(path2, 0) != -1) {
 			/* We are in an MSys2-based setup */
 			int len2 = GetEnvironmentVariable(L"HOME", NULL, 0);
@@ -658,8 +688,13 @@ int main(void)
 	LPWSTR working_directory = NULL;
 
 	/* Determine MSys2-based Git path. */
-	swprintf(msystem_bin, sizeof(msystem_bin),
-		L"mingw%d\\bin", (int) sizeof(void *) * 8);
+	if (IsRunningOnARM64()) {
+		swprintf(msystem_bin, sizeof(msystem_bin),
+			L"arm64\\bin");
+	} else {
+		swprintf(msystem_bin, sizeof(msystem_bin),
+			L"mingw%d\\bin", (int) sizeof(void *) * 8);
+	}
 	*top_level_path = L'\0';
 
 	/* get the installation location */