Add support for reading msdos MZ executables.

See email thread starting here:  https://www.sourceware.org/ml/binutils/2018-01/msg00001.html

include	* coff/msdos.h: New header.
	* coff/pe.h: Move common defines to msdos.h.
	* coff/powerpc.h: Likewise.

bfd	* i386msdos.c (msdos_mkobject); New function.
	(msdos_object_p): New function.
	(i386_msdos_vec): Use msdos_object_p as the check_format
	function.
	* peicode.h: Rename external_PEI_DOS_hdr, DOSMAGIC, and
	NT_SIGNATURE to external_DOS_hdr, IMAGE_DOS_SIGNATURE, and
	IMAGE_NT_SIGNATURE.
	* peXXigen.c: Likewise.
	* coff-ia64.c: Likewise.

3 files changed, 59 insertions, 31 deletions

diff --git a/include/coff/msdos.h b/include/coff/msdos.h
new file mode 100644
index 0000000..cebd957
--- /dev/null
+++ b/include/coff/msdos.h
@@ -0,0 +1,57 @@
+/* msdos.h  -  MS-DOS and derived executable header information
+
+   Copyright (C) 1999-2018 Free Software Foundation, Inc.
+
+   This file is part of BFD, the Binary File Descriptor library.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software Foundation,
+   Inc., 51 Franklin Street - Fifth Floor, Boston, MA 02110-1301, USA.  */
+#ifndef _MSDOS_H
+#define _MSDOS_H
+
+#define IMAGE_DOS_SIGNATURE	0x5a4d		/* MZ */
+#define IMAGE_OS2_SIGNATURE	0x454e		/* NE */
+#define IMAGE_OS2_SIGNATURE_LE	0x454c		/* LE */
+#define IMAGE_OS2_SIGNATURE_LX	0x584c		/* LX */
+#define IMAGE_NT_SIGNATURE	0x00004550	/* PE\0\0 */
+
+struct external_DOS_hdr
+{
+  /* DOS header fields - always at offset zero in the EXE file.  */
+  char e_magic[2];		/* Magic number.  */
+  char e_cblp[2];		/* Bytes on last page of file.  */
+  char e_cp[2];			/* Pages in file.  */
+  char e_crlc[2];		/* Relocations.  */
+  char e_cparhdr[2];		/* Size of header in paragraphs.  */
+  char e_minalloc[2];		/* Minimum extra paragraphs needed.  */
+  char e_maxalloc[2];		/* Maximum extra paragraphs needed.  */
+  char e_ss[2];			/* Initial (relative) SS value.  */
+  char e_sp[2];			/* Initial SP value.  */
+  char e_csum[2];		/* Checksum.  */
+  char e_ip[2];			/* Initial IP value.  */
+  char e_cs[2];			/* Initial (relative) CS value.  */
+  char e_lfarlc[2];		/* File address of relocation table.  */
+  char e_ovno[2];		/* Overlay number.  */
+  char e_res[4][2];		/* Reserved words, all 0x0.  */
+  char e_oemid[2];		/* OEM identifier.  */
+  char e_oeminfo[2];		/* OEM information.  */
+  char e_res2[10][2];		/* Reserved words, all 0x0.  */
+  char e_lfanew[4];		/* File address of new exe header, usually 0x80.  */
+  char dos_message[16][4];	/* Other stuff, always follow DOS header.  */
+};
+
+/* The actual DOS header only includes up to the e_ovno field.  */
+#define DOS_HDR_SIZE		(offsetof (struct external_DOS_hdr, e_res))
+
+#endif /* _MSDOS_H */
diff --git a/include/coff/pe.h b/include/coff/pe.h
index f9035bf..56cc4e2 100644
--- a/include/coff/pe.h
+++ b/include/coff/pe.h
@@ -20,6 +20,8 @@
 #ifndef _PE_H
 #define _PE_H
 
+#include "msdos.h"
+
 /* NT specific file attributes.  */
 #define IMAGE_FILE_RELOCS_STRIPPED           0x0001
 #define IMAGE_FILE_EXECUTABLE_IMAGE          0x0002
@@ -168,40 +170,11 @@
 #define IMAGE_SUBSYSTEM_SAL_RUNTIME_DRIVER	13
 #define IMAGE_SUBSYSTEM_XBOX			14
 
-/* Magic values that are true for all dos/nt implementations.  */
-#define DOSMAGIC       0x5a4d
-#define NT_SIGNATURE   0x00004550
-
 /* NT allows long filenames, we want to accommodate this.
    This may break some of the bfd functions.  */
 #undef  FILNMLEN
 #define FILNMLEN	18	/* # characters in a file name.  */
 
-struct external_PEI_DOS_hdr
-{
-  /* DOS header fields - always at offset zero in the EXE file.  */
-  char e_magic[2];		/* Magic number, 0x5a4d.  */
-  char e_cblp[2];		/* Bytes on last page of file, 0x90.  */
-  char e_cp[2];			/* Pages in file, 0x3.  */
-  char e_crlc[2];		/* Relocations, 0x0.  */
-  char e_cparhdr[2];		/* Size of header in paragraphs, 0x4.  */
-  char e_minalloc[2];		/* Minimum extra paragraphs needed, 0x0.  */
-  char e_maxalloc[2];		/* Maximum extra paragraphs needed, 0xFFFF.  */
-  char e_ss[2];			/* Initial (relative) SS value, 0x0.  */
-  char e_sp[2];			/* Initial SP value, 0xb8.  */
-  char e_csum[2];		/* Checksum, 0x0.  */
-  char e_ip[2];			/* Initial IP value, 0x0.  */
-  char e_cs[2];			/* Initial (relative) CS value, 0x0.  */
-  char e_lfarlc[2];		/* File address of relocation table, 0x40.  */
-  char e_ovno[2];		/* Overlay number, 0x0.  */
-  char e_res[4][2];		/* Reserved words, all 0x0.  */
-  char e_oemid[2];		/* OEM identifier (for e_oeminfo), 0x0.  */
-  char e_oeminfo[2];		/* OEM information; e_oemid specific, 0x0.  */
-  char e_res2[10][2];		/* Reserved words, all 0x0.  */
-  char e_lfanew[4];		/* File address of new exe header, usually 0x80.  */
-  char dos_message[16][4];	/* Other stuff, always follow DOS header.  */
-};
-
 struct external_PEI_IMAGE_hdr
 {
   char nt_signature[4];		/* Required NT signature, 0x4550.  */
diff --git a/include/coff/powerpc.h b/include/coff/powerpc.h
index 37fef42..a5e56fb 100644
--- a/include/coff/powerpc.h
+++ b/include/coff/powerpc.h
@@ -37,8 +37,6 @@
 
 /* extra NT defines */
 #define PPCMAGIC       0760         /* peeked on aa PowerPC Windows NT box */
-#define DOSMAGIC       0x5a4d       /* from arm.h, i386.h */
-#define NT_SIGNATURE   0x00004550   /* from arm.h, i386.h */
 
 /* from winnt.h */
 #define IMAGE_NT_OPTIONAL_HDR_MAGIC        0x10b