dos_file.S revision 1.1
1 /* $NetBSD: dos_file.S,v 1.1 2024/06/29 13:45:14 rin Exp $ */ 2 3 /* extracted from Tor Egge's patches for NetBSD boot */ 4 5 #include <machine/asm.h> 6 7 /* 8 # MSDOS call "INT 0x21 Function 0x3d" to open a file. 9 # Call with %ah = 0x3d 10 # %al = 0x0 (access and sharing modes) 11 # %ds:%dx = ASCIZ filename 12 # %cl = attribute mask of files to look for 13 */ 14 15 .globl _C_LABEL(doserrno) 16 _C_LABEL(doserrno): .long 1 17 18 ENTRY(dosopen) 19 .code32 20 pushl %ebp 21 movl %esp, %ebp 22 pushl %edx 23 pushl %ebx 24 pushl %esi 25 pushl %edi 26 27 movl 0x8(%ebp), %edx # File name. 28 29 call _C_LABEL(prot_to_real) # enter real mode 30 .code16 31 32 push %ds 33 movl %edx, %eax 34 shrl $4, %eax 35 mov %ds, %si 36 add %si, %ax 37 mov %ax, %ds 38 and $0xf, %dx 39 40 movb $0x3d, %ah # Open existing file. 41 movb $0x0 , %al # ro 42 43 sti 44 int $0x21 45 cli 46 pop %ds 47 48 jnc ok1 49 mov %ax, _C_LABEL(doserrno) 50 movl $-1, %edx 51 jmp err1 52 ok1: 53 movl $0,%edx 54 mov %ax, %dx 55 err1: 56 calll _C_LABEL(real_to_prot) # back to protected mode 57 .code32 58 59 movl %edx, %eax # return value in %eax 60 61 popl %edi 62 popl %esi 63 popl %ebx 64 popl %edx 65 popl %ebp 66 ret 67 68 ENTRY(dosread) 69 .code32 70 pushl %ebp 71 movl %esp, %ebp 72 pushl %ebx 73 pushl %ecx 74 pushl %edx 75 pushl %esi 76 pushl %edi 77 78 movl 0x8(%ebp), %ebx # File handle 79 movl 0xc(%ebp), %edx # Buffer. 80 movl 0x10(%ebp), %ecx # Bytes to read 81 82 call _C_LABEL(prot_to_real) # enter real mode 83 .code16 84 85 push %ds 86 movl %edx, %eax 87 shrl $4, %eax 88 mov %ds, %si 89 add %si, %ax 90 mov %ax, %ds 91 and $0xf, %dx 92 93 movb $0x3f, %ah # Read from file or device 94 95 sti 96 int $0x21 97 cli 98 pop %ds 99 100 jnc ok2 101 mov %ax, _C_LABEL(doserrno) 102 movl $-1, %edx 103 jmp err2 104 ok2: 105 movl $0,%edx 106 mov %ax, %dx 107 err2: 108 calll _C_LABEL(real_to_prot) # back to protected mode 109 .code32 110 111 movl %edx, %eax # return value in %eax 112 113 popl %edi 114 popl %esi 115 popl %edx 116 popl %ecx 117 popl %ebx 118 popl %ebp 119 ret 120 121 ENTRY(dosclose) 122 .code32 123 pushl %ebp 124 movl %esp, %ebp 125 pushl %ebx 126 pushl %esi 127 pushl %edi 128 129 movl 0x8(%ebp), %ebx # File handle 130 131 call _C_LABEL(prot_to_real) # enter real mode 132 .code16 133 134 movb $0x3e, %ah # Close file. 135 136 sti 137 int $0x21 138 cli 139 140 jnc ok3 141 mov %ax, _C_LABEL(doserrno) 142 movl $-1, %ebx 143 jmp err3 144 ok3: 145 movl $0, %ebx 146 err3: 147 calll _C_LABEL(real_to_prot) # back to protected mode 148 .code32 149 150 movl %ebx, %eax # return value in %eax 151 152 popl %edi 153 popl %esi 154 popl %ebx 155 popl %ebp 156 ret 157 158 ENTRY(dosseek) 159 .code32 160 pushl %ebp 161 movl %esp, %ebp 162 pushl %ebx 163 pushl %ecx 164 pushl %edx 165 pushl %esi 166 pushl %edi 167 168 movl 0x8(%ebp), %ebx # File handle 169 movl 0xc(%ebp), %ecx # Offset 170 movl 0x10(%ebp) , %edx # whence 171 172 call _C_LABEL(prot_to_real) # enter real mode 173 .code16 174 175 movb $0x42, %ah # Seek 176 movb %dl, %al # whence 177 mov %cx, %dx #offs lo 178 shrl $0x10, %ecx #offs hi 179 180 sti 181 int $0x21 182 cli 183 184 jnc ok4 185 mov %ax, _C_LABEL(doserrno) 186 movl $-1, %edx 187 jmp err4 188 ok4: 189 shll $0x10, %edx #new ofs hi 190 mov %ax, %dx #new ofs lo 191 err4: 192 calll _C_LABEL(real_to_prot) # back to protected mode 193 .code32 194 195 movl %edx, %eax # return value in %eax 196 197 popl %edi 198 popl %esi 199 popl %edx 200 popl %ecx 201 popl %ebx 202 popl %ebp 203 ret 204
Indexes created Mon Sep 29 21:09:56 GMT 2025