btxldr: future-proof argument passing from boot1/2-ish to loader

Place the arguments at a fixed offset of 0x800 withing the argument area
(of size 0x1000).  Allow variable size extended arguments first of which
should be a size of the extended arguments (including the size
parameter).

Consolidate all related definitions in a new i386/common/bootargs.h header.

Many thanks to jhb and bde for their guidance and reviews.

Reviewed by:	jhb, bde
Approved by:	jhb
MFC after:	1 month

sys/boot/i386/btx/btx/Makefile

@@ -12,6 +12,7 @@ BOOT_BTX_FLAGS=0x0
 .endif
 
 CFLAGS+=-DBTX_FLAGS=${BOOT_BTX_FLAGS}
+CFLAGS+=-I${.CURDIR}/../../common
 
 .if defined(BTX_SERIAL)
 BOOT_COMCONSOLE_PORT?= 0x3f8

sys/boot/i386/btx/btx/btx.S

@@ -15,6 +15,8 @@
  * $FreeBSD$
  */
 
+#include <bootargs.h>
+
 /*
  * Memory layout.
  */
@@ -205,7 +207,7 @@ init.8: 	xorl %ecx,%ecx			# Zero
 		movl $MEM_USR,%edx		# User base address
 		movzwl %ss:BDA_MEM,%eax 	# Get free memory
 		shll $0xa,%eax			# To bytes
-		subl $0x1000,%eax		# Less arg space
+		subl $ARGSPACE,%eax		# Less arg space
 		subl %edx,%eax			# Less base
 		movb $SEL_UDATA,%cl		# User data selector
 		pushl %ecx			# Set SS

sys/boot/i386/btx/btxldr/Makefile

@@ -6,6 +6,7 @@ NO_MAN=
 SRCS=	btxldr.S
 
 CFLAGS+=-DLOADER_ADDRESS=${LOADER_ADDRESS}
+CFLAGS+=-I${.CURDIR}/../../common
 
 .if defined(BTXLDR_VERBOSE)
 CFLAGS+=-DBTXLDR_VERBOSE

sys/boot/i386/btx/btxldr/btxldr.S

@@ -15,6 +15,8 @@
  * $FreeBSD$
  */
 
+#include <bootargs.h>
+
 #define	RBX_MUTE	0x10	/* -m */
 #define	OPT_SET(opt)	(1 << (opt))
 
@@ -89,7 +91,7 @@ start:		cld				# String ops inc
 		call hexout			#  stack
 		call putstr			#  pointer
 		movl $m_args,%esi		# Format string
-		leal 0x4(%esp,1),%ebx		# First argument
+		leal 0x4(%esp),%ebx		# First argument
 		movl $0x6,%ecx			# Count
 start.1:	movl (%ebx),%eax		# Get argument and
 		addl $0x4,%ebx			#  bump pointer
@@ -97,24 +99,28 @@ start.1:	movl (%ebx),%eax		# Get argument and
 		loop start.1			# Till done
 		call putstr			# End message
 #endif
-		movl $0x48,%ecx 		# Allocate space
-		subl %ecx,%ebp			#  for bootinfo
-		movl 0x18(%esp,1),%esi		# Source: bootinfo
+		movl BA_BOOTINFO+4(%esp),%esi	# Source: bootinfo
 		cmpl $0x0, %esi			# If the bootinfo pointer
 		je start_null_bi		#  is null, don't copy it
+		movl BI_SIZE(%esi),%ecx 	# Allocate space
+		subl %ecx,%ebp			#  for bootinfo
 		movl %ebp,%edi			# Destination
 		rep				# Copy
 		movsb				#  it
-		movl %ebp,0x18(%esp,1)		# Update pointer
+		movl %ebp,BA_BOOTINFO+4(%esp)	# Update pointer
+		movl %edi,%ebp			# Restore base pointer
 #ifdef BTXLDR_VERBOSE
 		movl $m_rel_bi,%esi		# Display
 		movl %ebp,%eax			#  bootinfo
 		call hexout			#  relocation
 		call putstr			#  message
 #endif
-start_null_bi:	movl $0x18,%ecx 		# Allocate space
-		subl %ecx,%ebp			#  for arguments
-		leal 0x4(%esp,1),%esi		# Source
+start_null_bi:	movl $BOOTARGS_SIZE,%ecx 	# Fixed size of arguments
+		testl $KARGS_FLAGS_EXTARG, BA_BOOTFLAGS+4(%esp) # Check for extra data
+		jz start_fixed			# Skip if the flag is not set
+		addl BOOTARGS_SIZE+4(%esp),%ecx	# Add size of variable args
+start_fixed:	subl $ARGOFF,%ebp		# Place args at fixed offset
+		leal 0x4(%esp),%esi		# Source
 		movl %ebp,%edi			# Destination
 		rep				# Copy
 		movsb				#  them

sys/boot/i386/btx/lib/Makefile

@@ -3,7 +3,8 @@
 PROG=	crt0.o
 INTERNALPROG=
 NO_MAN=
-SRCS=	btxcsu.s btxsys.s btxv86.s
+SRCS=	btxcsu.S btxsys.s btxv86.s
+CFLAGS+=-I${.CURDIR}/../../common
 LDFLAGS=-Wl,-r
 
 .include <bsd.prog.mk>

sys/boot/i386/btx/lib/btxcsu.S

@@ -15,6 +15,8 @@
 
 # $FreeBSD$
 
+#include <bootargs.h>
+
 #
 # BTX C startup code (ELF).
 #
@@ -24,10 +26,6 @@
 #
 		.global _start
 #
-# Constants.
-#
-		.set ARGADJ,0xfa0		# Argument adjustment
-#
 # Client entry point.
 #
 _start: 	cld

sys/boot/i386/common/bootargs.h

@@ -0,0 +1,69 @@
+/*-
+ * Copyright (c) 2012 Andriy Gapon <avg@FreeBSD.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms are freely
+ * permitted provided that the above copyright notice and this
+ * paragraph and the following disclaimer are duplicated in all
+ * such forms.
+ *
+ * This software is provided "AS IS" and without any express or
+ * implied warranties, including, without limitation, the implied
+ * warranties of merchantability and fitness for a particular
+ * purpose.
+ *
+ * $FreeBSD$
+ */
+
+#ifndef _BOOT_I386_ARGS_H_
+#define	_BOOT_I386_ARGS_H_
+
+#define	KARGS_FLAGS_CD		0x1
+#define	KARGS_FLAGS_PXE		0x2
+#define	KARGS_FLAGS_ZFS		0x4
+#define	KARGS_FLAGS_EXTARG	0x8	/* variably sized extended argument */
+
+#define	BOOTARGS_SIZE	24	/* sizeof(struct bootargs) */
+#define	BA_BOOTFLAGS	8	/* offsetof(struct bootargs, bootflags) */
+#define	BA_BOOTINFO	20	/* offsetof(struct bootargs, bootinfo) */
+#define	BI_SIZE		48	/* offsetof(struct bootinfo, bi_size) */
+
+/*
+ * We reserve some space above BTX allocated stack for the arguments
+ * and certain data that could hang off them.  Currently only struct bootinfo
+ * is supported in that category.  The bootinfo is placed at the top
+ * of the arguments area and the actual arguments are placed at ARGOFF offset
+ * from the top and grow towards the top.  Hopefully we have enough space
+ * for bootinfo and the arguments to not run into each other.
+ * Arguments area below ARGOFF is reserved for future use.
+ */
+#define	ARGSPACE	0x1000	/* total size of the BTX args area */
+#define	ARGOFF		0x800	/* actual args offset within the args area */
+#define	ARGADJ		(ARGSPACE - ARGOFF)
+
+#ifndef __ASSEMBLER__
+
+struct bootargs
+{
+	uint32_t			howto;
+	uint32_t			bootdev;
+	uint32_t			bootflags;
+	union {
+		struct {
+			uint32_t	pxeinfo;
+			uint32_t	reserved;
+		};
+		uint64_t		zfspool;
+	};
+	uint32_t			bootinfo;
+
+	/*
+	 * If KARGS_FLAGS_EXTARG is set in bootflags, then the above fields
+	 * are followed by a uint32_t field that specifies a size of the
+	 * extended arguments (including the size field).
+	 */
+};
+
+#endif /*__ASSEMBLER__*/
+
+#endif	/* !_BOOT_I386_ARGS_H_ */

sys/boot/i386/loader/main.c

@@ -39,28 +39,17 @@ __FBSDID("$FreeBSD$");
 #include <sys/reboot.h>
 
 #include "bootstrap.h"
+#include "common/bootargs.h"
 #include "libi386/libi386.h"
 #include "btxv86.h"
 
-#define	KARGS_FLAGS_CD		0x1
-#define	KARGS_FLAGS_PXE		0x2
-#define	KARGS_FLAGS_ZFS		0x4
+CTASSERT(sizeof(struct bootargs) == BOOTARGS_SIZE);
+CTASSERT(offsetof(struct bootargs, bootinfo) == BA_BOOTINFO);
+CTASSERT(offsetof(struct bootargs, bootflags) == BA_BOOTFLAGS);
+CTASSERT(offsetof(struct bootinfo, bi_size) == BI_SIZE);
 
 /* Arguments passed in from the boot1/boot2 loader */
-static struct 
-{
-    u_int32_t	howto;
-    u_int32_t	bootdev;
-    u_int32_t	bootflags;
-    union {
-	struct {
-	    u_int32_t	pxeinfo;
-	    u_int32_t	res2;
-	};
-	uint64_t	zfspool;
-    };
-    u_int32_t	bootinfo;
-} *kargs;
+static struct bootargs *kargs;
 
 static u_int32_t	initial_howto;
 static u_int32_t	initial_bootdev;

sys/boot/i386/zfsboot/zfsboot.c

@@ -41,9 +41,7 @@ __FBSDID("$FreeBSD$");
 #include "drv.h"
 #include "util.h"
 #include "cons.h"
-
-/* Hint to loader that we came from ZFS */
-#define	KARGS_FLAGS_ZFS		0x4
+#include "bootargs.h"
 
 #define PATH_DOTCONFIG	"/boot.config"
 #define PATH_CONFIG	"/boot/config"