8l: add DOS stub to PE binaries

R=rsc
CC=golang-dev
https://golang.org/cl/915041

src/cmd/ld/pe.c

@@ -11,6 +11,28 @@
 #include "../ld/lib.h"
 #include "../ld/pe.h"
 
+// DOS stub that prints out
+// "This program cannot be run in DOS mode."
+static char dosstub[] =
+{
+	0x4d, 0x5a, 0x90, 0x00, 0x03, 0x00, 0x04, 0x00,
+	0x00, 0x00, 0x00, 0x00, 0xff, 0xff, 0x00, 0x00,
+	0x8b, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+	0x40, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+	0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+	0x00, 0x00, 0x00, 0x00, 0x80, 0x00, 0x00, 0x00,
+	0x0e, 0x1f, 0xba, 0x0e, 0x00, 0xb4, 0x09, 0xcd,
+	0x21, 0xb8, 0x01, 0x4c, 0xcd, 0x21, 0x54, 0x68,
+	0x69, 0x73, 0x20, 0x70, 0x72, 0x6f, 0x67, 0x72,
+	0x61, 0x6d, 0x20, 0x63, 0x61, 0x6e, 0x6e, 0x6f,
+	0x74, 0x20, 0x62, 0x65, 0x20, 0x72, 0x75, 0x6e,
+	0x20, 0x69, 0x6e, 0x20, 0x44, 0x4f, 0x53, 0x20,
+	0x6d, 0x6f, 0x64, 0x65, 0x2e, 0x0d, 0x0d, 0x0a,
+	0x24, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
+};
+
 static int pe64;
 static int nsect;
 static int sect_virt_begin;
@@ -64,8 +86,7 @@ pewrite(void)
 {
 	int i, j;
 
-	strnput("MZ", 0x3c);
-	LPUT(0x40);	// file offset to PE header
+	write(cout, dosstub, sizeof dosstub);
 	strnput("PE", 4);
 
 	for (i=0; i<sizeof(fh); i++)