allow /dev/reboot to handle elf executables, from sources.
i'm guessing that this is motivated by the boot loader on the
mikrotek routerboard.

Reference: /n/atom/patch/applied2013/rebootelf
Date: Wed Jul 31 20:55:39 CES 2013
Signed-off-by: quanstro@quanstro.net

--- /sys/src/9/port/portdat.h	Wed Jul 31 20:54:13 2013
+++ /sys/src/9/port/portdat.h	Wed Jul 31 20:54:14 2013
@@ -9,6 +9,7 @@
 typedef struct Edf	Edf;
 typedef struct Egrp	Egrp;
 typedef struct Evalue	Evalue;
+typedef struct Execvals	Execvals;
 typedef struct Fgrp	Fgrp;
 typedef struct DevConf	DevConf;
 typedef struct Image	Image;
@@ -761,6 +762,12 @@
 	READSTR =	4000,		/* temporary buffer size for device reads */
 };
 
+struct Execvals {
+	uvlong	entry;
+	ulong	textsize;
+	ulong	datasize;
+};
+
 extern	Conf	conf;
 extern	char*	conffile;
 extern	int	cpuserver;
@@ -774,6 +781,7 @@
 extern 	Ref	noteidalloc;
 extern	int	nsyscall;
 extern	Palloc	palloc;
+	int	(*parseboothdr)(Chan *, ulong, Execvals *);
 extern	Queue*	serialoq;
 extern	char*	statename[];
 extern	Image	swapimage;
--- /sys/src/9/port/rebootcmd.c	Wed Jul 31 20:54:15 2013
+++ /sys/src/9/port/rebootcmd.c	Wed Jul 31 20:54:15 2013
@@ -4,19 +4,24 @@
 #include	"dat.h"
 #include	"fns.h"
 #include	"../port/error.h"
-#include	"a.out.h"
-
-static ulong
-l2be(long l)
-{
-	uchar *cp;
-
-	cp = (uchar*)&l;
-	return (cp[0]<<24) | (cp[1]<<16) | (cp[2]<<8) | cp[3];
-}
+#include	<a.out.h>
+#include 	"/sys/src/libmach/elf.h"
 
+enum {
+	Ehdr32sz	= 52,
+	Phdr32sz	= 32,
+	Shdr32sz	= 40,
+
+	Ehdr64sz	= 64,
+	Phdr64sz	= 56,
+	Shdr64sz	= 64,
+};
+
+static uchar elfident[] = {
+	'\177', 'E', 'L', 'F',
+};
 
-static void
+void
 readn(Chan *c, void *vp, long n)
 {
 	char *p = vp;
@@ -32,6 +37,49 @@
 	}
 }
 
+/* assume the elf header is in the byte order of this machine */
+static int
+readelfhdr(Chan *c, ulong, Execvals *evp)
+{
+	Ehdr ehdr;
+	Phdr phdrs[3];
+
+	c->offset = 0;			/* back up */
+	readn(c, &ehdr, sizeof ehdr);
+	if(memcmp(&ehdr.ident[MAG0], elfident, sizeof elfident) != 0 ||
+	    ehdr.ident[CLASS] != ELFCLASS32)
+		return -1;
+
+	/* get textsize and datasize from Phdrs */
+	readn(c, phdrs, sizeof phdrs);
+	evp->entry = ehdr.elfentry;
+	evp->textsize = phdrs[0].filesz;
+	evp->datasize = phdrs[1].filesz;
+	c->offset = ROUNDUP(Ehdr32sz + 3*Phdr32sz, 16);	/* position for text */
+	return 0;
+}
+
+static int
+readelf64hdr(Chan *c, ulong, Execvals *evp)
+{
+	E64hdr ehdr;
+	P64hdr phdrs[3];
+
+	c->offset = 0;			/* back up */
+	readn(c, &ehdr, sizeof ehdr);
+	if(memcmp(&ehdr.ident[MAG0], elfident, sizeof elfident) != 0 ||
+	    ehdr.ident[CLASS] != ELFCLASS64)
+		return -1;
+
+	/* get textsize and datasize from Phdrs */
+	readn(c, phdrs, sizeof phdrs);
+	evp->entry = ehdr.elfentry;
+	evp->textsize = phdrs[0].filesz;
+	evp->datasize = phdrs[1].filesz;
+	c->offset = ROUNDUP(Ehdr64sz + 3*Phdr64sz, 16);	/* position for text */
+	return 0;
+}
+
 static void
 setbootcmd(int argc, char *argv[])
 {
@@ -55,6 +103,7 @@
 {
 	Chan *c;
 	Exec exec;
+	Execvals ev;
 	ulong magic, text, rtext, entry, data, size;
 	uchar *p;
 
@@ -69,11 +118,25 @@
 
 	readn(c, &exec, sizeof(Exec));
 	magic = l2be(exec.magic);
-	entry = l2be(exec.entry);
-	text = l2be(exec.text);
-	data = l2be(exec.data);
-	if(magic != AOUT_MAGIC)
+	/*
+	 * AOUT_MAGIC is sometimes defined like this:
+	 * #define AOUT_MAGIC	V_MAGIC || magic==M_MAGIC
+	 * so we can only use it in a fairly stylized manner.
+	 */
+	if(magic == AOUT_MAGIC) {
+		entry = l2be(exec.entry);
+		text = l2be(exec.text);
+		data = l2be(exec.data);
+	} else if(parseboothdr && (*parseboothdr)(c, magic, &ev) >= 0 ||
+	    readelfhdr(c, magic, &ev) >= 0 ||
+	    readelf64hdr(c, magic, &ev) >= 0){
+		entry = ev.entry;
+		text = ev.textsize;
+		data = ev.datasize;
+	} else {
 		error(Ebadexec);
+		return;				/* for the compiler */
+	}
 
 	/* round text out to page boundary */
 	rtext = PGROUND(entry+text)-entry;
--- /sys/src/9/port/sysproc.c	Wed Jul 31 20:54:17 2013
+++ /sys/src/9/port/sysproc.c	Wed Jul 31 20:54:18 2013
@@ -205,7 +205,7 @@
 	return pid;
 }
 
-static ulong
+ulong
 l2be(long l)
 {
 	uchar *cp;
--- /sys/src/9/port/portfns.h	Wed Jul 31 20:54:19 2013
+++ /sys/src/9/port/portfns.h	Wed Jul 31 20:54:20 2013
@@ -154,6 +154,7 @@
 void		ksetenv(char*, char*, int);
 void		kstrcpy(char*, char*, int);
 void		kstrdup(char**, char*);
+ulong		l2be(long);
 long		latin1(Rune*, int);
 int		lock(Lock*);
 void		logopen(Log*);
@@ -298,6 +299,7 @@
 void		randominit(void);
 ulong		randomread(void*, ulong);
 void		rdb(void);
+void		readn(Chan *, void *, long);
 int		readnum(ulong, char*, ulong, ulong, int);
 int		readstr(ulong, char*, ulong, char*);
 void		ready(Proc*);