Add support for directly booting from FAT12 filesystems.
This shouldn't really be needed except that Linux wont mount a small FAT16 filesystem - it always treats it as FAT12 even when you tell it otherwise. There was enough free space before the main FS on the USB stick I've been using for an extra small FAT fs to boot from.
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dsl
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cf1caa71e2
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@ -1,6 +1,7 @@
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# $NetBSD: Makefile,v 1.2 2007/01/06 20:47:15 dsl Exp $
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# $NetBSD: Makefile,v 1.3 2012/03/10 23:59:36 dsl Exp $
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SUBDIR= fat16
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SUBDIR= fat16
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SUBDIR+= fat12
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.include <bsd.subdir.mk>
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.include <bsd.obj.mk>
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6
sys/arch/i386/stand/fatboot/fat12/Makefile
Normal file
6
sys/arch/i386/stand/fatboot/fat12/Makefile
Normal file
@ -0,0 +1,6 @@
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# $NetBSD: Makefile,v 1.1 2012/03/10 23:59:36 dsl Exp $
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PROG=bootxx_fat12
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FAT_ENTRY_SIZE=12
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.include <../Makefile.fat>
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@ -1,4 +1,4 @@
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/* $NetBSD: fatboot.S,v 1.3 2008/04/29 06:53:02 martin Exp $ */
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/* $NetBSD: fatboot.S,v 1.4 2012/03/10 23:59:36 dsl Exp $ */
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/*-
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* Copyright (c) 2007 The NetBSD Foundation, Inc.
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@ -50,10 +50,12 @@
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#endif
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/* Support for FAT32 could be added - but hasn't been yet. */
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#if FAT_ENTRY_SIZE != 16
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#if FAT_ENTRY_SIZE != 16 && FAT_ENTRY_SIZE != 12
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#error Unsupported FAT_ENTRY_SIZE value
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#endif
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#define FAT_SIZE_STR (('0'+ FAT_ENTRY_SIZE / 10) | ('0' + FAT_ENTRY_SIZE % 10) << 8)
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#define PBR_AFTERBPB 62 /* BPB size in floppy master BR */
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#ifdef TERSE_ERROR
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@ -112,8 +114,13 @@ start0:
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mov %sp, %bp /* to access the pbp */
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push %dx /* save drive at -2(%bp) */
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/* We put the LBA bios command block on stack.
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* Since we only want a 32bit sector number, stack a zero */
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push %cs /* %cs is zero */
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push %cs /* 64-bit for LBA read */
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set_err(ERR_NOT_FAT16)
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cmpl $'A'|'T'<<8|'1'<<16|'6'<<24, bs_file_sys_type+1(%bp)
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cmpl $'A'|'T'<<8|FAT_SIZE_STR<<16, bs_file_sys_type+1(%bp)
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jne error
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/* Add 'reserved' (inside ptn) to 'hidden' (ptn offset) */
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@ -121,14 +128,21 @@ start0:
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addl bpb_hidden_secs(%bp), %eax
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mov %eax, fat_sector(%bp) /* To get first sector of FAT */
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#if FAT_ENTRY_SIZE == 12
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/* Read the entire FAT */
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push %eax
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push %ds
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push $fat_buffer
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push $12 /* 12 sectors is assumed 6k */
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call read_lba
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#endif
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/* Determine base of root directory */
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movzbw bpb_FATs(%bp), %ax /* Count of FATs */
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mulw bpb_FAT_secs(%bp) /* FAT size in %dx:%ax */
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shl $16,%edx
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xchg %ax,%dx /* FAT size now in %edx */
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addl fat_sector(%bp), %edx /* Directory is after FATs */
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push %cs /* %cs is zero */
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push %cs /* 64-bit for LBA read */
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pushl %edx /* Sector number of root dir */
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push $0x1000 /* Read to 0x10000:0 */
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@ -149,7 +163,7 @@ start0:
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/* Read in the entire root directory */
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push %ax /* Sectors in root directory */
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cwtl
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addl %eax, %edx /* %edx now sector of first file */
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addl %eax, %edx /* %edx now sector of first cluster */
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call read_lba /* Read entire directory */
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/* Scan directory for our file */
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@ -195,16 +209,16 @@ found_boot:
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jnz 1b
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dec %cx
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dec %cx
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movw %es:15(%di), %ax /* Cluster number for file start */
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movw %es:(26-11)(%di), %ax /* Cluster number for file start */
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push %es /* We increment the 'segment' ... */
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pop %di /* ... after each read, offset is 0 */
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read_data_block:
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mov %ax, %bx /* Save cluster number */
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shl %cl, %eax /* Convert to sector number */
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add %eax, %edx
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pushl %edx /* Sector to read */
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sub %eax, %edx /* Recover base segment */
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jz error /* Sanity bail-out */
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add %edx, %eax
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pushl %eax /* Sector to read */
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push %di /* Target address segment! */
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push $0
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push sec_p_cl_w(%bp)
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@ -218,6 +232,20 @@ read_data_block:
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/* Lookup FAT slot number in FAT table */
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mov %bx, %ax /* Recover cluster number */
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#if FAT_ENTRY_SIZE == 12
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shr $1, %ax
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jc 1f
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add %ax, %bx
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mov fat_buffer(%bx), %ax
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and $0xf,%ah
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jmp 2f
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1: add %ax, %bx
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mov fat_buffer(%bx), %ax
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shr $4, %ax
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2:
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cmp $0x0fff, %ax
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jb read_data_block
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#else
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push %dx
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xor %dx, %dx
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divw bpb_bytes_per_sec(%bp)
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@ -243,6 +271,7 @@ lookup_fat:
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movzwl fat_buffer(%bx), %eax /* Next FAT slot */
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cmp $0xfff0, %ax
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jb read_data_block
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#endif
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/* Found end of FAT chain - must be EOF - leap into loaded code */
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mov $0x1000, %ax
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@ -255,7 +284,7 @@ err1: jmp error
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/* Set parameters expected by /boot */
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magic_ok:
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mov bpb_hidden_secs(%bp), %ebx /* ptn base sector */
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movb -2(%bp), %dl /* disk number (could pop %dx) */
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movb -2(%bp), %dl /* disk number */
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mov $boot_params + 4, %si
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push %es
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push $0
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@ -286,6 +315,7 @@ read_lba:
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#include <message.S>
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#if 0
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#include <dump_eax.S>
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dump_eax_buff = start
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#endif
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errtxt: .ascii "Error " /* runs into newline... */
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@ -296,7 +326,9 @@ newline:
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#ifndef TERSE_ERROR
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ERR_READ: .asciz "Disk read"
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ERR_NO_BOOT: .asciz "No /boot"
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ERR_NOT_FAT16: .asciz "Not FAT16 ptn"
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ERR_NOT_FAT16: .ascii "Not FAT"
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.word FAT_SIZE_STR
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.asciz " ptn"
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ERR_NO_BOOT_MAGIC_2: .asciz "No magic in /boot"
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#endif
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@ -321,3 +353,4 @@ fat_cache: .word 0xffff /* Sector number in buffer */
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. = _C_LABEL(start) + 0x1fe
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.word 0xaa55
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fat_buffer: /* 2 sectors worth of FAT table */
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/* 6k for FAT12 */
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