From 058dd028ac7d8ae217d1b3b00213751d63034195 Mon Sep 17 00:00:00 2001 From: "H. Peter Anvin" Date: Fri, 5 Sep 2008 14:49:42 -0700 Subject: ISOLINUX: support for hybrid mode (CD-ROM/USB key) Still a work in progress. Signed-off-by: H. Peter Anvin --- mbr/Makefile | 12 ++-- mbr/isohdpfx.S | 212 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 219 insertions(+), 5 deletions(-) create mode 100644 mbr/isohdpfx.S (limited to 'mbr') diff --git a/mbr/Makefile b/mbr/Makefile index 7952e60b..a57b3946 100644 --- a/mbr/Makefile +++ b/mbr/Makefile @@ -17,23 +17,25 @@ topdir = .. include $(topdir)/MCONFIG.embedded -all: mbr.bin gptmbr.bin +all: mbr.bin gptmbr.bin isohdpfx.bin .PRECIOUS: %.o %.o: %.S $(CC) $(SFLAGS) -Wa,-a=$*.lst -c -o $@ $< -mbr.elf: mbr.o mbr.ld +.PRECIOUS: %.elf +%.elf: %.o mbr.ld $(LD) $(LDFLAGS) -T mbr.ld -e _start -o $@ $< mbr.bin: mbr.elf checksize.pl $(OBJCOPY) -O binary $< $@ $(PERL) checksize.pl mbr.bin 440 -mbr_bin.c: mbr.bin +isohdpfx.bin: isohdpfx.elf checksize.pl + $(OBJCOPY) -O binary $< $@ + $(PERL) checksize.pl mbr.bin 432 -gptmbr.elf: gptmbr.o mbr.ld - $(LD) $(LDFLAGS) -T mbr.ld -e _start -o $@ $< +mbr_bin.c: mbr.bin gptmbr.bin: gptmbr.elf checksize.pl $(OBJCOPY) -O binary $< $@ diff --git a/mbr/isohdpfx.S b/mbr/isohdpfx.S new file mode 100644 index 00000000..f2bc7dc6 --- /dev/null +++ b/mbr/isohdpfx.S @@ -0,0 +1,212 @@ +/* ----------------------------------------------------------------------- + * + * Copyright 2007-2008 H. Peter Anvin - All Rights Reserved + * + * Permission is hereby granted, free of charge, to any person + * obtaining a copy of this software and associated documentation + * files (the "Software"), to deal in the Software without + * restriction, including without limitation the rights to use, + * copy, modify, merge, publish, distribute, sublicense, and/or + * sell copies of the Software, and to permit persons to whom + * the Software is furnished to do so, subject to the following + * conditions: + * + * The above copyright notice and this permission notice shall + * be included in all copies or substantial portions of the Software. + * + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, + * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES + * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND + * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT + * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, + * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING + * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR + * OTHER DEALINGS IN THE SOFTWARE. + * + * ----------------------------------------------------------------------- */ + +/* + * Modified MBR code used on an ISO image in hybrid mode. + * + * This doesn't follow the El Torito spec at all -- it is just a stub + * loader of a hard-coded offset, but that's good enough to load + * ISOLINUX. + */ + + .code16 + .text + +HYBRID_MAGIC = 0x7078c0fb +isolinux_hybrid_signature = 0x7c00+64 +isolinux_start_hybrid = 0x7c00+64+4 + + .globl bootsec +/* Important: the top 6 words on the stack are passed to isolinux.bin */ +stack = 0x7c00 +driveno = (stack-6) +sectors = (stack-8) +heads = (stack-10) +secpercyl = (stack-14) + +BIOS_page = 0x462 + + /* gas/ld has issues with doing this as absolute addresses... */ + .section ".bootsec", "a", @nobits + .globl bootsec +bootsec: + .space 512 + + .text + .globl _start +_start: + + cli + xorw %ax, %ax + movw %ax, %ds + movw %ax, %ss + movw $stack, %sp + movw %sp, %si + pushw %es /* es:di -> $PnP header */ + pushw %di + pushw %dx /* dl -> drive number */ + movw %ax, %es + sti + cld + + /* Copy down to 0:0x600 */ + movw $_start, %di + movw $(512/2), %cx + rep; movsw + + ljmpw $0, $next + +next: + /* Check to see if we have EBIOS */ + pushw %dx /* drive number */ + movb $0x41, %ah /* %al == 0 already */ + movw $0x55aa, %bx + xorw %cx, %cx + xorb %dh, %dh + stc + int $0x13 + jc 1f + cmpw $0xaa55, %bx + jne 1f + shrw %cx /* Bit 0 = fixed disk subset */ + jnc 1f + + /* We have EBIOS; patch in the following code at + read_sector_cbios: movb $0x42, %ah ; jmp read_common */ + movl $0xeb42b4+((read_common-read_sector_cbios-4) << 24), \ + (read_sector_cbios) + +1: + popw %dx + + /* Get (C)HS geometry */ + movb $0x08, %ah + int $0x13 + andw $0x3f, %cx /* Sector count */ + pushw %cx /* Save sectors on the stack */ + movzbw %dh, %ax /* dh = max head */ + incw %ax /* From 0-based max to count */ + pushw %ax /* Save heads on the stack */ + mulw %cx /* Heads*sectors -> sectors per cylinder */ + + /* Save sectors/cylinder on the stack */ + pushw %dx /* High word */ + pushw %ax /* Low word */ + + /* + * Load sectors. We do this one at a time mostly to avoid + * pitfalls and to share code with the stock MBR code. + */ + movw $0x7c00, %bx + movw $4, %cx /* Sector count */ + movl (lba_offset), %eax + +2: + call read_sector + jc disk_error + incl %eax + addw $512, %bx + loopw 2b + + /* + * Okay, that actually worked... update the stack pointer + * and jump into isolinux.bin... + */ + cmpl $HYBRID_MAGIC,(isolinux_hybrid_signature) + jne bad_signature + + cli + movw $heads, %sp + jmp isolinux_start_hybrid + +bad_signature: + call error + .ascii "isolinux.bin missing or corrupt.\r\n" + +/* + * read_sector: read a single sector pointed to by %eax to %es:%bx. + * CF is set on error. All registers saved. + */ +read_sector: + pushal + xorl %edx, %edx + pushl %edx /* MSW of LBA */ + pushl %eax /* LSW of LBA */ + pushw %es /* Buffer segment */ + pushw %bx /* Buffer offset */ + pushw $1 /* Sector count */ + pushw $16 /* Size of packet */ + movw %sp, %si + + /* This chunk is skipped if we have ebios */ + /* Do not clobber %eax before this chunk! */ + /* This also relies on %bx and %edx as set up above. */ +read_sector_cbios: + divl (secpercyl) + shlb $6, %ah + movb %ah, %cl + movb %al, %ch + xchgw %dx, %ax + divb (sectors) + movb %al, %dh + orb %ah, %cl + incw %cx /* Sectors are 1-based */ + movw $0x0201, %ax + +read_common: + movb (driveno), %dl + int $0x13 + addw $16, %sp /* Drop DAPA */ + popal + ret + +disk_error: + call error + .ascii "Operating system load error.\r\n" + +/* + * Print error messages. This is invoked with "call", with the + * error message at the return address. + */ +error: + popw %si +2: + lodsb + movb $0x0e, %ah + movb (BIOS_page), %bh + movb $0x07, %bl + int $0x10 /* May destroy %bp */ + cmpb $10, %al /* Newline? */ + jne 2b + + int $0x18 /* Boot failure */ +die: + hlt + jmp die + + /* Address of pointer to isolinux.bin */ +lba_offset = _start+432 -- cgit v1.2.1