Split bootsector execution code out into bootsector.c.

Added basic El Torito ISO image boot capability
2025-12-31 15:25:23 +03:00 · 2007-01-29 04:21:38 +00:00
parent bde8878eef
commit 2cf1e33df1
7 changed files with 610 additions and 68 deletions
--- a/src/arch/i386/image/bootsector.c
+++ b/src/arch/i386/image/bootsector.c
@@ -0,0 +1,111 @@
+/*
+ * Copyright (C) 2007 Michael Brown <mbrown@fensystems.co.uk>.
+ *
+ * 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 2 of the
+ * License, or 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., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+/**
+ * @file
+ *
+ * x86 bootsector image format
+ *
+ */
+
+#include <errno.h>
+#include <realmode.h>
+#include <biosint.h>
+#include <bootsector.h>
+
+/** Vector for storing original INT 18 handler
+ *
+ * We do not chain to this vector, so there is no need to place it in
+ * .text16.
+ */
+static struct segoff int18_vector;
+
+/** Vector for storing original INT 19 handler
+ *
+ * We do not chain to this vector, so there is no need to place it in
+ * .text16.
+ */
+static struct segoff int19_vector;
+
+/** Restart point for INT 18 or 19 */
+extern void bootsector_exec_fail ( void );
+
+/**
+ * Jump to preloaded bootsector
+ *
+ * @v segment		Real-mode segment
+ * @v offset		Real-mode offset
+ * @v drive		Drive number to pass to boot sector
+ * @ret rc		Return status code
+ */
+int call_bootsector ( unsigned int segment, unsigned int offset,
+		      unsigned int drive ) {
+	int discard_b, discard_D, discard_d;
+
+	DBG ( "Booting from boot sector at %04x:%04x\n", segment, offset );
+
+	/* Hook INTs 18 and 19 to capture failure paths */
+	hook_bios_interrupt ( 0x18, ( unsigned int ) bootsector_exec_fail,
+			      &int18_vector );
+	hook_bios_interrupt ( 0x19, ( unsigned int ) bootsector_exec_fail,
+			      &int19_vector );
+
+	/* Boot the loaded sector
+	 *
+	 * We assume that the boot sector may completely destroy our
+	 * real-mode stack, so we preserve everything we need in
+	 * static storage.
+	 */
+	__asm__ __volatile__ ( REAL_CODE ( /* Save return address off-stack */
+					   "popw %%cs:saved_retaddr\n\t"
+					   /* Save stack pointer */
+					   "movw %%ss, %%ax\n\t"
+					   "movw %%ax, %%cs:saved_ss\n\t"
+					   "movw %%sp, %%cs:saved_sp\n\t"
+					   /* Jump to boot sector */
+					   "pushw %%bx\n\t"
+					   "pushw %%di\n\t"
+					   "lret\n\t"
+					   /* Preserved variables */
+					   "\nsaved_ss: .word 0\n\t"
+					   "\nsaved_sp: .word 0\n\t"
+					   "\nsaved_retaddr: .word 0\n\t"
+					   /* Boot failure return point */
+					   "\nbootsector_exec_fail:\n\t"
+					   /* Restore stack pointer */
+					   "movw %%cs:saved_ss, %%ax\n\t"
+					   "movw %%ax, %%ss\n\t"
+					   "movw %%cs:saved_sp, %%sp\n\t"
+					   /* Return via saved address */
+					   "jmp *%%cs:saved_retaddr\n\t" )
+			       : "=b" ( discard_b ), "=D" ( discard_D ),
+			         "=d" ( discard_d )
+			       : "b" ( segment ), "D" ( offset ),
+			         "d" ( drive )
+			       : "eax", "ecx", "esi", "ebp" );
+
+	DBG ( "Booted disk returned via INT 18 or 19\n" );
+
+	/* Unhook INTs 18 and 19 */
+	unhook_bios_interrupt ( 0x18, ( unsigned int ) bootsector_exec_fail,
+				&int18_vector );
+	unhook_bios_interrupt ( 0x19, ( unsigned int ) bootsector_exec_fail,
+				&int19_vector );
+	
+	return -ECANCELED;
+}