WIP try to use MSVCRT.DLL instead of UCRT

Very simple "hello world" style programs work.

builder/builtins.go

@@ -3,6 +3,7 @@ package builder
 import (
 	"os"
 	"path/filepath"
+	"strings"
 
 	"github.com/tinygo-org/tinygo/compileopts"
 	"github.com/tinygo-org/tinygo/goenv"
@@ -229,6 +230,10 @@ var libCompilerRT = Library{
 			builtins = append(builtins, avrBuiltins...)
 		case "x86_64", "aarch64", "riscv64": // any 64-bit arch
 			builtins = append(builtins, genericBuiltins128...)
+		case "i386":
+			if strings.Split(target, "-")[2] == "windows" {
+				builtins = append(builtins, "i386/chkstk.S")
+			}
 		}
 		return builtins, nil
 	},

builder/mingw-w64.go

@@ -32,23 +32,54 @@ var libMinGW = Library{
 		mingwDir := filepath.Join(goenv.Get("TINYGOROOT"), "lib/mingw-w64")
 		return []string{
 			"-nostdlibinc",
+			"-isystem", mingwDir + "/mingw-w64-crt/include",
 			"-isystem", mingwDir + "/mingw-w64-headers/crt",
+			"-isystem", mingwDir + "/mingw-w64-headers/include",
 			"-I", mingwDir + "/mingw-w64-headers/defaults/include",
 			"-I" + headerPath,
+			"-D__MSVCRT_VERSION__=0x700", // Microsoft Visual C++ .NET 2002
+			"-D_WIN32_WINNT=0x0501",      // target Windows XP
+			"-D__LIBMSVCRT_OS__",
+			"-D_CRTBLD",
+			"-Wno-pragma-pack",
 		}
 	},
 	librarySources: func(target string) ([]string, error) {
 		// These files are needed so that printf and the like are supported.
-		sources := []string{
+		var sources []string
-			"mingw-w64-crt/stdio/ucrt_fprintf.c",
+		if strings.Split(target, "-")[0] == "i386" {
-			"mingw-w64-crt/stdio/ucrt_fwprintf.c",
+			// Old 32-bit x86 systems use msvcrt.dll.
-			"mingw-w64-crt/stdio/ucrt_printf.c",
+			sources = []string{
-			"mingw-w64-crt/stdio/ucrt_snprintf.c",
+				"mingw-w64-crt/crt/pseudo-reloc.c",
-			"mingw-w64-crt/stdio/ucrt_sprintf.c",
+				"mingw-w64-crt/gdtoa/dmisc.c",
-			"mingw-w64-crt/stdio/ucrt_vfprintf.c",
+				"mingw-w64-crt/gdtoa/gdtoa.c",
-			"mingw-w64-crt/stdio/ucrt_vprintf.c",
+				"mingw-w64-crt/gdtoa/gmisc.c",
-			"mingw-w64-crt/stdio/ucrt_vsnprintf.c",
+				"mingw-w64-crt/gdtoa/misc.c",
-			"mingw-w64-crt/stdio/ucrt_vsprintf.c",
+				"mingw-w64-crt/misc/___mb_cur_max_func.c",
+				"mingw-w64-crt/misc/lc_locale_func.c",
+				"mingw-w64-crt/misc/mbrtowc.c",
+				"mingw-w64-crt/misc/strnlen.c",
+				"mingw-w64-crt/misc/wcrtomb.c",
+				"mingw-w64-crt/secapi/rand_s.c",
+				"mingw-w64-crt/stdio/acrt_iob_func.c",
+				"mingw-w64-crt/stdio/mingw_lock.c",
+				"mingw-w64-crt/stdio/mingw_pformat.c",
+				"mingw-w64-crt/stdio/mingw_vfprintf.c",
+				"mingw-w64-crt/stdio/mingw_vsnprintf.c",
+			}
+		} else {
+			// Anything somewhat modern (amd64, arm64) uses UCRT.
+			sources = []string{
+				"mingw-w64-crt/stdio/ucrt_fprintf.c",
+				"mingw-w64-crt/stdio/ucrt_fwprintf.c",
+				"mingw-w64-crt/stdio/ucrt_printf.c",
+				"mingw-w64-crt/stdio/ucrt_snprintf.c",
+				"mingw-w64-crt/stdio/ucrt_sprintf.c",
+				"mingw-w64-crt/stdio/ucrt_vfprintf.c",
+				"mingw-w64-crt/stdio/ucrt_vprintf.c",
+				"mingw-w64-crt/stdio/ucrt_vsnprintf.c",
+				"mingw-w64-crt/stdio/ucrt_vsprintf.c",
+			}
 		}
 		return sources, nil
 	},
@@ -63,27 +94,40 @@ var libMinGW = Library{
 func makeMinGWExtraLibs(tmpdir, goarch string) []*compileJob {
 	var jobs []*compileJob
 	root := goenv.Get("TINYGOROOT")
-	// Normally all the api-ms-win-crt-*.def files are all compiled to a single
+	var libs []string
-	// .lib file. But to simplify things, we're going to leave them as separate
+	if goarch == "386" {
-	// files.
+		libs = []string{
-	for _, name := range []string{
+			// x86 uses msvcrt.dll instead of UCRT for compatibility with old
-		"kernel32.def.in",
+			// Windows versions.
-		"api-ms-win-crt-conio-l1-1-0.def",
+			"advapi32.def.in",
-		"api-ms-win-crt-convert-l1-1-0.def.in",
+			"kernel32.def.in",
-		"api-ms-win-crt-environment-l1-1-0.def",
+			"msvcrt.def.in",
-		"api-ms-win-crt-filesystem-l1-1-0.def",
+		}
-		"api-ms-win-crt-heap-l1-1-0.def",
+	} else {
-		"api-ms-win-crt-locale-l1-1-0.def",
+		// Use the modernized UCRT on new systems.
-		"api-ms-win-crt-math-l1-1-0.def.in",
+		// Normally all the api-ms-win-crt-*.def files are all compiled to a
-		"api-ms-win-crt-multibyte-l1-1-0.def",
+		// single .lib file. But to simplify things, we're going to leave them
-		"api-ms-win-crt-private-l1-1-0.def.in",
+		// as separate files.
-		"api-ms-win-crt-process-l1-1-0.def",
+		libs = []string{
-		"api-ms-win-crt-runtime-l1-1-0.def.in",
+			"kernel32.def.in",
-		"api-ms-win-crt-stdio-l1-1-0.def",
+			"api-ms-win-crt-conio-l1-1-0.def",
-		"api-ms-win-crt-string-l1-1-0.def",
+			"api-ms-win-crt-convert-l1-1-0.def.in",
-		"api-ms-win-crt-time-l1-1-0.def",
+			"api-ms-win-crt-environment-l1-1-0.def",
-		"api-ms-win-crt-utility-l1-1-0.def",
+			"api-ms-win-crt-filesystem-l1-1-0.def",
-	} {
+			"api-ms-win-crt-heap-l1-1-0.def",
+			"api-ms-win-crt-locale-l1-1-0.def",
+			"api-ms-win-crt-math-l1-1-0.def.in",
+			"api-ms-win-crt-multibyte-l1-1-0.def",
+			"api-ms-win-crt-private-l1-1-0.def.in",
+			"api-ms-win-crt-process-l1-1-0.def",
+			"api-ms-win-crt-runtime-l1-1-0.def.in",
+			"api-ms-win-crt-stdio-l1-1-0.def",
+			"api-ms-win-crt-string-l1-1-0.def",
+			"api-ms-win-crt-time-l1-1-0.def",
+			"api-ms-win-crt-utility-l1-1-0.def",
+		}
+	}
+	for _, name := range libs {
 		outpath := filepath.Join(tmpdir, filepath.Base(name)+".lib")
 		inpath := filepath.Join(root, "lib/mingw-w64/mingw-w64-crt/lib-common/"+name)
 		job := &compileJob{

compileopts/config.go

@@ -391,15 +391,25 @@ func (c *Config) LibcCFlags() []string {
 	case "mingw-w64":
 		root := goenv.Get("TINYGOROOT")
 		path, _ := c.LibcPath("mingw-w64")
-		return []string{
+		cflags := []string{
 			"-nostdlibinc",
 			"-isystem", filepath.Join(path, "include"),
 			"-isystem", filepath.Join(root, "lib", "mingw-w64", "mingw-w64-headers", "crt"),
 			"-isystem", filepath.Join(root, "lib", "mingw-w64", "mingw-w64-headers", "include"),
 			"-isystem", filepath.Join(root, "lib", "mingw-w64", "mingw-w64-headers", "defaults", "include"),
-			"-D_UCRT",
-			"-D_WIN32_WINNT=0x0a00", // target Windows 10
 		}
+		if c.GOARCH() == "386" {
+			cflags = append(cflags,
+				"-D__MSVCRT_VERSION__=0x700", // Microsoft Visual C++ .NET 2002
+				"-D_WIN32_WINNT=0x0501",      // target Windows XP
+			)
+		} else {
+			cflags = append(cflags,
+				"-D_UCRT",
+				"-D_WIN32_WINNT=0x0a00", // target Windows 10
+			)
+		}
+		return cflags
 	case "":
 		// No libc specified, nothing to add.
 		return nil

src/crypto/rand/rand_windows.go

@@ -21,6 +21,7 @@ func (r *reader) Read(b []byte) (n int, err error) {
 		// Call rand_s every four bytes because it's a C int (always 32-bit in
 		// Windows).
 		if i%4 == 0 {
+			// TODO: use RtlGenRandom on GOARCH=386.
 			errCode := libc_rand_s(&randomByte)
 			if errCode != 0 {
 				// According to the documentation, it can return an error.

src/runtime/runtime_windows.go

@@ -239,11 +239,17 @@ func procUnpin() {
 }
 
 func hardwareRand() (n uint64, ok bool) {
-	var n1, n2 uint32
+	if GOARCH == "386" {
-	errCode1 := libc_rand_s(&n1)
+		// Use the old RtlGenRandom, introduced in Windows XP.
-	errCode2 := libc_rand_s(&n2)
+		ok = RtlGenRandom(unsafe.Pointer(&n), 8)
-	n = uint64(n1)<<32 | uint64(n2)
+	} else {
-	ok = errCode1 == 0 && errCode2 == 0
+		// Use the newer secure rand_s function that's part of UCRT.
+		var n1, n2 uint32
+		errCode1 := libc_rand_s(&n1)
+		errCode2 := libc_rand_s(&n2)
+		n = uint64(n1)<<32 | uint64(n2)
+		ok = errCode1 == 0 && errCode2 == 0
+	}
 	return
 }
 
@@ -253,3 +259,10 @@ func hardwareRand() (n uint64, ok bool) {
 //
 //export rand_s
 func libc_rand_s(randomValue *uint32) int32
+
+// This function is part of advapi32.dll, and is called SystemFunction036 for
+// some reason. It's available on Windows XP and newer.
+// See: https://learn.microsoft.com/en-us/windows/win32/api/ntsecapi/nf-ntsecapi-rtlgenrandom
+//
+//export SystemFunction036
+func RtlGenRandom(buf unsafe.Pointer, len int) bool