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2 COMBOOT and COM32 files
5 SYSLINUX supports simple standalone programs, using a file format
6 similar to DOS ".com" files. A 32-bit version, called COM32, is also
7 provided. A simple API provides access to a limited set of filesystem
8 and console functions.
11 ++++ COMBOOT file format ++++
13 A COMBOOT file is a raw binary file containing 16-bit code. It should
14 be linked to run at offset 0x100, and contain no absolute segment
15 references. It is run in 16-bit real mode.
17 A COMBOOT image can be written to be compatible with MS-DOS. Such a
18 file will usually have extension ".com". A COMBOOT file which is not
19 compatible with MS-DOS will usually have extension ".cbt".
21 Before running the program, SYSLINUX sets up the following fields in
22 the Program Segment Prefix (PSP), a structure at offset 0 in the
23 program segment:
25 Offset Size Meaning
26 0 word Contains an INT 20h instruction
27 2 word Contains the paragraph (16-byte "segment" address) at
28 the end of memory available to the program.
29 128 byte Length of the command line arguments, including the leading
30 space but not including the final CR character.
31 129 127b Command line arguments, starting with a space and ending
32 with a CR character (ASCII 13).
34 The program is allowed to use memory between the PSP paragraph (which
35 all the CS, DS, ES and SS registers point to at program start) and the
36 paragraph value given at offset 2.
38 On startup, SP is set up to point to the end of the 64K segment, at
39 0xfffe. Under DOS it is possible for SP to contain a smaller
40 value if memory is very tight; this is never the case under SYSLINUX.
42 The program should make no assumptions about what segment address it
43 will be loaded at; instead it should look at the segment registers on
44 program startup. Both DOS and SYSLINUX will guarantee CS == DS == ES
45 == SS on program start; the program should not assume anything about
46 the values of FS or GS.
48 To exit, a program can either execute a near RET (which will jump to
49 offset 0 which contains an INT 20h instruction, terminating the
50 program), or execute INT 20h or INT 21h AH=00h or INT 21h AH=4Ch.
51 If compatiblity with SYSLINUX 1.xx is desired, use INT 20h.
54 ++++ COM32 file format ++++
56 A COM32 file is a raw binary file containing 32-bit code. It should
57 be linked to run at address 0x101000, and should not contain any
58 segment references. It will be run in flat-memory 32-bit protected
59 mode. Under SYSLINUX, it will be run in CPL 0, however, since it may
60 be possible to create a COM32 execution engine that would run under
61 something like Linux DOSEMU, it is recommended that the code does not
62 assume CPL 0 unless absolutely necessary.
64 It is highly recommended that every COM32 program begins with the byte
65 sequence B8 FF 4C CD 21 (mov eax,21cd4cffh) as a magic number.
67 A COM32 file should have extension ".c32".
69 On startup, CS will be set up as a flat 32-bit code segment, and DS ==
70 ES == SS will be set up as the equivalent flat 32-bit data segment.
71 FS and GS are reserved for future use and are currently initialized to
72 zero. A COM32 image should not assume any particular values of
73 segment selectors.
75 ESP is set up at the end of available memory and also serves as
76 notification to the program how much memory is available.
78 The following arguments are passed to the program on the stack:
80 Address Size Meaning
81 [ESP] dword Return (termination) address
82 [ESP+4] dword Number of additional arguments (currently 5)
83 [ESP+8] dword Pointer to the command line arguments (null-terminated string)
84 [ESP+12] dword Pointer to INT call helper function
85 [ESP+16] dword Pointer to low memory bounce buffer
86 [ESP+20] dword Size of low memory bounce buffer
87 [ESP+24] dword Pointer to FAR call helper function (new in 2.05)
88 [ESP+28] dword Pointer to CDECL helper function (new in 3.54)
90 This corresponds to the following C prototype, available in the file
91 com32/include/com32.h:
93 /* The standard prototype for _start() */
94 int _start(unsigned int __nargs,
95 char *__cmdline,
96 void (*__intcall)(uint8_t, com32sys_t *, com32sys_t *),
97 void *__bounce_ptr,
98 unsigned int __bounce_len,
99 void (*__farcall)(uint32_t, com32sys_t *, com32sys_t *),
100 int (*__cfarcall)(uint32_t, void *, size_t)
101 );
103 The intcall helper function can be used to issue BIOS or SYSLINUX API
104 calls, and takes the interrupt number as first argument. The second
105 argument is a pointer to the input register definition, an instance of
106 the following structure (available in <com32.h>):
108 typedef union {
109 uint32_t l;
110 uint16_t w[2];
111 uint8_t b[4];
112 } reg32_t;
114 typedef struct {
115 uint16_t gs; /* Offset 0 */
116 uint16_t fs; /* Offset 2 */
117 uint16_t es; /* Offset 4 */
118 uint16_t ds; /* Offset 6 */
120 reg32_t edi; /* Offset 8 */
121 reg32_t esi; /* Offset 12 */
122 reg32_t ebp; /* Offset 16 */
123 reg32_t _unused_esp; /* Offset 20 */
124 reg32_t ebx; /* Offset 24 */
125 reg32_t edx; /* Offset 28 */
126 reg32_t ecx; /* Offset 32 */
127 reg32_t eax; /* Offset 36 */
129 reg32_t eflags; /* Offset 40 */
130 } com32sys_t;
132 The third argument is a pointer to the output register definition, an
133 instance of the same structure. The third argument can also be zero
134 (NULL).
136 Since BIOS or SYSLINUX API calls can generally only manipulate data
137 below address 0x100000, a "bounce buffer" in low memory, at least 64K
138 in size, is available, to copy data in and out.
140 The farcall helper function behaves similarly, but takes as its first
141 argument the CS:IP (in the form (CS << 16) + IP) of procedure to be
142 invoked via a FAR CALL.
144 The cfarcall helper function takes (CS << 16)+IP, a pointer to a stack
145 frame, a size of that stack frame, and returns the return value of EAX
146 (which may need to be appropriate truncated by the user.)
149 ++++ SYSLINUX API CALLS +++
151 SYSLINUX provides the following API calls. SYSLINUX 1.xx only
152 supported INT 20h - terminate program. [] indicates the first version
153 of SYSLINUX which supported this feature (correctly.)
155 NOTE: Most of the API functionality is still experimental. Expect to
156 find bugs.
159 ++++ DOS-COMPATIBLE API CALLS ++++
161 INT 20h [1.48] Terminate program
162 INT 21h AH=00h [2.00] Terminate program
163 INT 21h AH=4Ch [2.00] Terminate program
165 All of these terminate the program.
168 INT 21h AH=01h [2.01] Get Key with Echo
170 Reads a key from the console input, with echo to the console
171 output. The read character is returned in AL. Extended
172 characters received from the keyboard are returned as NUL (00h)
173 + the extended character code.
176 INT 21h AH=02h [2.01] Write Character
178 Writes a character in DL to the console (video and serial)
179 output.
182 INT 21h AH=04h [2.01] Write Character to Serial Port
184 Writes a character in DL to the serial console output
185 (if enabled.) If no serial port is configured, this routine
186 does nothing.
189 INT 21h AH=08h [2.09] Get Key without Echo
191 Reads a key fron the console input, without echoing it to the
192 console output. The read character is returned in AL.
195 INT 21h AH=09h [2.01] Write DOS String to Console
197 Writes a DOS $-terminated string in DS:DX to the console.
200 INT 21h AH=0Bh [2.00] Check Keyboard
202 Returns AL=FFh if there is a keystroke waiting (which can then
203 be read with INT 21h, AH=01h or AH=08h), otherwise AL=00h.
206 INT 21h AH=30h [2.00] Check DOS Version
208 This function returns AX=BX=CX=DX=0, corresponding to a
209 hypothetical "DOS 0.0", but the high parts of EAX-EBX-ECX-EDX
210 spell "SYSLINUX":
212 EAX=59530000h EBX=4C530000h ECX=4E490000h EDX=58550000h
214 This function can thus be used to distinguish running on
215 SYSLINUX from running on DOS.
218 ++++ SYSLINUX-SPECIFIC API CALLS ++++
220 SYSLINUX-specific API calls are executed using INT 22h, with a
221 function number in AX. INT 22h is used by DOS for internal purposes;
222 do not execute INT 22h under DOS.
224 DOS-compatible function INT 21h, AH=30h can be used to detect if the
225 SYSLINUX API calls are available.
227 Any register not specifically listed as modified is preserved;
228 however, future versions of SYSLINUX may add additional output
229 registers to existing calls.
231 All calls return CF=0 on success, CF=1 on failure. The noted outputs
232 apply if CF=0 only unless otherwise noted. All calls clobber the
233 arithmetric flags (CF, PF, AF, ZF, SF and OF) but leave all other
234 flags unchanged unless otherwise noted.
237 AX=0001h [2.00] Get Version
239 Input: AX 0001h
240 Output: AX number of INT 22h API functions available
241 CH SYSLINUX major version number
242 CL SYSLINUX minor version number
243 DL SYSLINUX derivative ID (e.g. 32h = PXELINUX)
244 ES:SI SYSLINUX version string
245 ES:DI SYSLINUX copyright string
247 This API call returns the SYSLINUX version and API
248 information.
251 AX=0002h [2.01] Write String
253 Input: AX 0002h
254 ES:BX null-terminated string
255 Output: None
257 Writes a null-terminated string on the console.
260 AX=0003h [2.01] Run command
262 Input: AX 0003h
263 ES:BX null-terminated command string
264 Output: Does not return
266 This API call terminates the program and executes the command
267 string as if the user had entered it at the SYSLINUX command
268 line. This API call does not return.
271 AX=0004h [2.01] Run default command
273 Input: AX 0004h
274 Output: Does not return
276 This API call terminates the program and executes the default
277 command string as if the user had pressed Enter alone on the
278 SYSLINUX command line. This API call does not return.
281 AX=0005h [2.00] Force text mode
283 Input: AX 0005h
284 Output: None
286 If the screen was in graphics mode (due to displaying a splash
287 screen using the <Ctrl-X> command in a message file, or
288 similar), return to text mode.
291 AX=0006h [2.08] Open file
293 Input: AX 0006h
294 ES:SI null-terminated filename
295 Output: SI file handle
296 EAX length of file in bytes
297 CX file block size
299 Open a file for reading. The exact syntax of the filenames
300 allowed depends on the particular SYSLINUX derivative.
302 The SYSLINUX file system is block-oriented. The size of a
303 block will always be a power of two and no greater than 16K.
305 Note: SYSLINUX considers a zero-length file to be nonexistent.
308 AX=0007h [2.08] Read file
310 Input: AX 0007h
311 SI file handle
312 ES:BX buffer
313 CX number of blocks to read
314 Output: SI file handle, or 0 if EOF was reached
316 Read blocks from a file. Note that the file handle that is
317 returned in SI may not be the same value that was passed in.
319 If end of file was reached (SI=0), the file was automatically
320 closed.
322 The address of the buffer (ES:BX) should be at least 512-byte
323 aligned. SYSLINUX guarantees at least this alignment for the
324 COMBOOT load segment or the COM32 bounce buffer.
326 Keep in mind that a "file" may be a TFTP connection, and that
327 leaving a file open for an extended period of time may result
328 in a timeout.
330 WARNING: Calling this function with an invalid file handle
331 will probably crash the system.
334 AX=0008h [2.08] Close file
336 Input: AX 0008h
337 SI file handle
338 Output: None
340 Close a file before reaching the end of file.
342 WARNING: Calling this function with an invalid file handle
343 will probably crash the system.
346 AX=0009h [2.00] Call PXE Stack [PXELINUX ONLY]
348 Input: AX 0009h
349 BX PXE function number
350 ES:DI PXE parameter structure buffer
351 Output: AX PXE return status code
353 Invoke an arbitrary PXE stack function. On SYSLINUX/ISOLINUX,
354 this function returns with an error (CF=1) and no action is
355 taken. On PXELINUX, this function always returns with CF=0
356 indicating that the PXE stack was successfully invoked; check
357 the status code in AX and in the first word of the data buffer
358 to determine if the PXE call succeeded or not.
360 The PXE stack will have the UDP stack OPEN; if you change that
361 you cannot call any of the file-related API functions, and
362 must restore UDP OPEN before returning to PXELINUX.
364 PXELINUX reserves UDP port numbers from 49152 to 65535 for its
365 own use; port numbers below that range is available.
368 AX=000Ah [2.00] Get Derivative-Specific Information
370 [SYSLINUX, EXTLINUX]
371 Input: AX 000Ah
372 CL 9 (to get a valid return in CL for all versions)
373 Output: AL 31h (SYSLINUX), 34h (EXTLINUX)
374 DL drive number
375 CL sector size as a power of 2 (9 = 512 bytes) [3.35]
376 ES:BX pointer to partition table entry (if DL >= 80h)
377 FS:SI pointer to initial ES:DI value [3.53]
379 Note: This function was broken in EXTLINUX 3.00-3.02.
381 On boot, ES:DI is supposed to point to the BIOS $PnP
382 structure, although in practice most operating systems
383 will search for it in memory. However, preserving
384 this while chainloading is probably a good idea.
386 Note that FS:SI is a pointer to a memory location
387 containing the original ES:DI value, not the value
388 itself.
391 [PXELINUX]
392 Input: AX 000Ah
393 Output: AL 32h (PXELINUX)
394 DX PXE API version detected (DH=major, DL=minor)
395 ES:BX pointer to PXENV+ or !PXE structure
396 FS:SI pointer to original stack with invocation record
398 Note: DX notes the API version detected by PXELINUX,
399 which may be more conservative than the actual version
400 available. For exact information examine the API
401 version entry in the PXENV+ structure, or the API
402 version entries in the ROMID structures pointed from
403 the !PXE structure.
405 PXELINUX will use, and provide, the !PXE structure
406 over the PXENV+ structure. Examine the structure
407 signature to determine which particular structure was
408 provided.
410 The FS:SI pointer points to the top of the original stack
411 provided by the PXE stack, with the following values
412 pushed at the time PXELINUX is started:
414 [fs:si+0] GS <- top of stack
415 [fs:si+2] FS
416 [fs:si+4] ES
417 [fs:si+6] DS
418 [fs:si+8] EDI
419 [fs:si+12] ESI
420 [fs:si+16] EBP
421 [fs:si+20] -
422 [fs:si+24] EBX
423 [fs:si+28] EDX
424 [fs:si+32] ECX
425 [fs:si+36] EAX
426 [fs:si+40] EFLAGS
427 [fs:si+44] PXE return IP <- t.o.s. when PXELINUX invoked
428 [fs:si+46] PXE return CS
431 [ISOLINUX]
432 Input: AX 000Ah
433 Output: AL 33h (ISOLINUX)
434 DL drive number
435 CL 11 (sector size as a power of 2) [3.35]
436 ES:BX pointer to El Torito spec packet
437 FS:SI pointer to initial ES:DI value [3.53]
439 Note: Some very broken El Torito implementations do
440 not provide the spec packet information. If so, ES:BX
441 may point to all zeroes or to garbage. Call INT 13h,
442 AX=4B01h to obtain the spec packet directly from the
443 BIOS if necessary.
445 This call gives information specific to a particular SYSLINUX
446 derivative. The value returned in AL is the same as is
447 returned in DL by INT 22h AX=0001h.
450 AX=000Bh [2.00] Get Serial Console Configuration
452 Input: AX 000Bh
453 Output: DX serial port I/O base (e.g. 3F8h = COM1...)
454 CX baud rate divisor (1 = 115200 bps, 2 = 57600 bps...)
455 BX flow control configuration bits (see syslinux.doc)
456 -> bit 15 is set if the video console is disabled
458 If no serial port is configured, DX will be set to 0 and the
459 other registers are undefined.
462 AX=000Ch [2.00] Perform final cleanup
463 Input: AX 000Ch
464 DX derivative-specific flags (0000h = clean up all)
465 Output: None
467 This routine performs any "final cleanup" the boot loader
468 would normally perform before loading a kernel, such as
469 unloading the PXE stack in the case of PXELINUX. AFTER
470 INVOKING THIS CALL, NO OTHER API CALLS MAY BE INVOKED, NOR MAY
471 THE PROGRAM TERMINATE AND RETURN TO THE BOOT LOADER. This
472 call basically tells the boot loader "get out of the way, I'll
473 handle it from here."
475 For COM32 images, the boot loader will continue to provide
476 interrupt and BIOS call thunking services as long its memory
477 areas (0x0800-0xffff, 0x100000-0x100fff) are not overwritten.
478 MAKE SURE TO DISABLE INTERRUPTS, AND INSTALL NEW GDT AND IDTS
479 BEFORE OVERWRITING THESE MEMORY AREAS.
481 The permissible values for DX is an OR of these values:
483 SYSLINUX: 0000h Normal cleanup
485 PXELINUX: 0000h Normal cleanup
486 0003h Keep UNDI and PXE stacks loaded
488 ISOLINUX: 0000h Normal cleanup
490 EXTLINUX: 0000h Normal cleanup
492 All other values are undefined, and may have different
493 meanings in future versions of SYSLINUX.
496 AX=000Dh [2.08] Cleanup and replace bootstrap code
497 Input: AX 000Dh
498 DX derivative-specific flags (see previous function)
499 EDI bootstrap code (linear address, can be in high memory)
500 ECX bootstrap code length in bytes (must fit in low mem)
501 EBX(!) initial value of EDX after bootstrap
502 ESI initial value of ESI after bootstrap
503 DS initial value of DS after bootstrap
504 Output: Does not return
506 This routine performs final cleanup, then takes a piece of
507 code, copies it over the primary bootstrap at address 7C00h,
508 and jumps to it. This can be used to chainload boot sectors,
509 MBRs, bootstraps, etc.
511 Normal boot sectors expect DL to contain the drive number,
512 and, for hard drives (DL >= 80h) DS:SI to contain a pointer to
513 the 16-byte partition table entry. The memory between
514 600h-7FFh is available to put the partition table entry in.
516 For PXELINUX, if the PXE stack is not unloaded, all registers
517 (except DS, ESI and EDX) and the stack will be set up as they
518 were set up by the PXE ROM.
521 AX=000Eh [2.11] Get configuration file name
522 Input: AX 0000Eh
523 Output: ES:BX null-terminated file name string
525 Returns the name of the configuration file. Note that it is
526 possible that the configuration file doesn't actually exist.
529 AX=000Fh [3.00] Get IPAPPEND strings [PXELINUX]
530 Input: AX 000Fh
531 Output: CX number of strings (currently 2)
532 ES:BX pointer to an array of NEAR pointers in
533 the same segment, one for each of the above
534 strings
536 Returns the same strings that the "ipappend" option would have
537 added to the command line, one for each bit of the "ipappend"
538 flag value, so entry 0 is the "ip=" string and entry 1 is the
539 "BOOTIF=" string.
542 AX=0010h [3.00] Resolve hostname [PXELINUX]
543 Input: ES:BX pointer to null-terminated hostname
544 Output: EAX IP address of hostname (zero if not found)
546 Queries the DNS server(s) for a specific hostname. If the
547 hostname does not contain a dot (.), the local domain name
548 is automatically appended.
550 This function only return CF=1 if the function is not
551 supported. If the function is supported, but the hostname did
552 not resolve, it returns with CF=0, EAX=0.
554 The IP address is returned in network byte order, i.e. if the
555 IP address is 1.2.3.4, EAX will contain 0x04030201. Note that
556 all uses of IP addresses in PXE are also in network byte order.
559 AX=0011h [3.05] Maximum number of shuffle descriptors
560 Input: AX 0011h
561 Output: CX maximum number of descriptors
563 This routine reports the maximum number of shuffle descriptors
564 permitted in a call to function 0012h.
566 Typical values are 682 and 1365.
569 AX=0012h [3.50] Cleanup, shuffle and boot
570 Input: AX 0012h
571 DX derivative-specific flags (see function 000Ch)
572 ES:DI shuffle descriptor list (must be in low memory)
573 CX number of shuffle descriptors
574 EBX(!) initial value of EDX after bootstrap
575 ESI initial value of ESI after bootstrap
576 DS initial value of DS after bootstrap
577 EBP CS:IP of routine to jump to
578 Output: Does not return
579 (if CX is too large the routine returns with CF=1)
581 This routine performs final cleanup, then performs a sequence
582 of copies, and jumps to a specified real mode entry point.
583 This is a more general version of function 000Dh, which can
584 also be used to load other types of programs.
586 The copies must not touch memory below address 7C00h.
588 ES:DI points to a list of CX descriptors each of the form:
590 Offset Size Meaning
591 0 dword destination address
592 4 dword source address
593 8 dword length in bytes
595 The copies are overlap-safe, like memmove().
597 Starting in version 3.50, if the source address is -1
598 (FFFFFFFFh) then the block specified by the destination
599 address and the length is set to all zero.
601 Starting in version 3.50, if the destination address is -1
602 (FFFFFFFFh) then the data block is loaded as a new set of
603 descriptors, and processing is continued (and unprocessed
604 descriptors are lost, this is thus typically only used as the
605 last descriptor in a block.) The block must still fit in the
606 internal descriptor buffer (see function 0011h), but can, of
607 course, itself chain another block.
610 Normal boot sectors expect DL to contain the drive number,
611 and, for hard drives (DL >= 80h) DS:SI to contain a pointer to
612 the 16-byte partition table entry. The memory between
613 600h-7FFh is available to put the partition table entry in.
615 For PXELINUX, if the PXE stack is not unloaded, all registers
616 (except DS, ESI and EDX) and the stack will be set up as they
617 were set up by the PXE ROM.
619 This interface was probably broken before version 3.50.
622 AX=0013h [3.08] Idle loop call
623 Input: AX 0013h
624 Output: None
626 Call this routine while sitting in an idle loop. It performs
627 any periodic activities required by the filesystem code. At
628 the moment, this is a no-op on all derivatives except
629 PXELINUX, where it executes PXE calls to answer ARP queries.
631 Starting with version 3.10, this API call harmlessly returns
632 failure (CF=1) if invoked on a platform which does not need
633 idle calls. Additionally, it's safe to call this API call on
634 previous SYSLINUX versions (2.00 or later); it will just
635 harmlessly fail. Thus, if this call returns failure (CF=1),
636 it means that there is no technical reason to call this
637 function again, although doing so is of course safe.
640 AX=0014h [3.10] Local boot [PXELINUX, ISOLINUX]
641 Input: AX 0014h
642 DX Local boot parameter
643 Output: Does not return
645 This function invokes the equivalent of the "localboot"
646 configuration file option. The parameter in DX is the same
647 parameter as would be entered after "localboot" in the
648 configuration file; this parameter is derivative-specific --
649 see syslinux.doc for the definition.
652 AX=0015h [3.10] Get feature flags
653 Input: AX 0015h
654 Output: ES:BX pointer to flags in memory
655 CX number of flag bytes
657 This function reports whether or not this SYSLINUX version and
658 derivative supports specific features. Keep in mind that
659 future versions might have more bits; remember to treat any
660 bits beyond the end of the array (as defined by the value in
661 CX) as zero.
663 Currently the following feature flag is defined:
665 Byte Bit Definition
666 ----------------------------------------------------
667 0 0 Local boot (AX=0014h) supported
668 1 Idle loop call (AX=0013h) is a no-op
670 All other flags are reserved.
673 AX=0016h [3.10] Run kernel image
674 Input: AX 0016h
675 DS:SI Filename of kernel image (zero-terminated string)
676 ES:BX Command line (zero-terminated string)
677 ECX IPAPPEND flags [PXELINUX]
678 EDX Type of file (since 3.50)
679 Output: Does not return if successful; returns with CF=1 if
680 the kernel image is not found.
682 This function is similiar to AX=0003h Run command, except that
683 the filename and command line are treated as if specified in a
684 KERNEL and APPEND statement of a LABEL statement, which means:
686 - The filename has to be exact; no variants are tried;
687 - No global APPEND statement is applied;
688 - ALLOWOPTIONS and IMPLICIT statements in the configuration
689 file do not apply. It is therefore important that the
690 COMBOOT module doesn't allow the end user to violate the
691 intent of the administrator.
693 Additionally, this function returns with a failure if the file
694 doesn't exist, instead of returning to the command line. (It
695 may still return to the command line if the image is somehow
696 corrupt, however.)
698 The file types are defined as follows:
700 Equivalent
701 EDX Config Extensions Type of file
702 0 KERNEL Determined by filename extension
703 1 LINUX none Linux kernel image
704 2 BOOT .bs .bin Bootstrap program
705 3 BSS .bss Boot sector with patch [SYSLINUX]
706 4 PXE .0 PXE Network Bootstrap Prog [PXELINUX]
707 5 FDIMAGE .img Floppy disk image [ISOLINUX]
708 6 COMBOOT .com .cbt 16-bit COMBOOT program
709 7 COM32 .c32 COM32 program
710 8 CONFIG Configuration file
713 AX=0017h [3.30] Report video mode change
714 Input: AX 0017h
715 BX Video mode flags
716 Bit 0: graphics mode
717 Bit 1: non-default mode
718 Bit 2: VESA mode
719 Bit 3: text functions not supported
720 CX For graphics modes, pixel columns
721 DX For graphics modes, pixel rows
722 Output: None
724 This function is used to report video mode changes to
725 SYSLINUX. It does NOT actually change the video mode, but
726 rather, allows SYSLINUX to take appropriate action in response
727 to a video mode change. Modes that cannot be exited either
728 with the conventional BIOS mode set command (INT 10h, AH=00h)
729 or the VESA VBE mode set command (INT 10h, AX=4F02h) should
730 not be used.
732 This function returns with a failure if BX contains any bits
733 which are undefined in the current version of SYSLINUX.
735 The following bits in BX are currently defined:
737 Bit 0: graphics mode
739 Indicates that the mode is a graphics mode, as opposed
740 to a text mode.
742 Bit 1: non-standard mode
744 A non-standard mode is any mode except text mode and
745 graphics mode 0012h (VGA 640x480, 16 color.)
747 Bit 2: VESA mode
749 This mode is a VESA mode, and has to be exited with
750 the VESA VBE API (INT 10h, AX=4F02h) as opposed to the
751 conventional BIOS API (INT 10h, AH=00h).
753 Bit 3: Text functions not supported
755 This indicates that the BIOS text output functions
756 (INT 10h, AH=02h, 03h, 06h, 09h, 0Eh, 11h) don't work.
757 If this bit is set, SYSLINUX will reset the mode
758 before printing any characters on the screen.
760 This is common for VESA modes.
763 AX=0018h [3.30] Query custom font
764 Input: AX 0018h
765 Output: AL Height of custom font in scan lines, or zero
766 ES:BX Pointer to custom font in memory
768 This call queries if a custom display font has been loaded via
769 the "font" configuration file command. If no custom font has
770 been loaded, AL contains zero.
773 AX=0019h [3.50] Read disk [SYSLINUX, ISOLINUX, EXTLINUX]
774 Input: AX 0019h
775 EDX Sector number
776 ESI Reserved - MUST BE ZERO
777 EDI Reserved - MUST BE ZERO
778 CX Sector count
779 ES:BX Buffer address
780 Output: None
782 Read disk blocks from the active filesystem (partition); for
783 disks, sector number zero is the boot sector. For ISOLINUX,
784 this call reads the CD-ROM.
786 For compatiblity with all systems, the buffer should
787 *neither* cross 64K boundaries, *nor* wrap around the segment.
789 This routine reports "boot failed" (and does not return) on
790 disk error.
793 AX=001Ah [3.50] Cleanup, shuffle and boot to flat protected mode
794 Input: AX 001Ah
795 DX derivative-specific flags (see function 000Ch)
796 ES:DI shuffle descriptor list (must be in low memory)
797 CX number of shuffle descriptors
798 DS:SI pointer to register values (must be in low memory)
799 Output: Does not return
800 (if CX is too large the routine returns with CF=1)
802 This routine performs final cleanup, then performs a sequence
803 of copies, and jumps to a specified protected mode entry point.
804 This is otherwise similar to function 0012h; see that function
805 for the meaning of ES:DI and CX.
807 DS:SI points to the initial register file, which is a structure
808 of 9 dwords (available in <syslinux/bootpm.h>):
810 struct syslinux_pm_regs {
811 uint32_t eax; /* Offset 0 */
812 uint32_t ecx; /* Offset 4 */
813 uint32_t edx; /* Offset 8 */
814 uint32_t ebx; /* Offset 12 */
815 uint32_t esp; /* Offset 16 */
816 uint32_t ebp; /* Offset 20 */
817 uint32_t esi; /* Offset 24 */
818 uint32_t edi; /* Offset 28 */
820 uint32_t eip; /* Offset 32 */
821 };
823 Protected mode is entered with all data segments set up as a
824 flat 32-bit read/write segment and the code segment a flat 32-bit
825 read/execute segment. Interrupts and paging is off, CPL=0, DF=0;
826 however, GDT, LDT and IDT are undefined, so it is up to the
827 invoked code to set new descriptor tables to its liking.
830 AX=001Bh [3.50] Cleanup, shuffle and boot to real mode
831 Input: AX 001Bh
832 DX derivative-specific flags (see function 000Ch)
833 ES:DI shuffle descriptor list (must be in low memory)
834 CX number of shuffle descriptors
835 DS:SI pointer to register values (must be in low memory)
836 Output: Does not return
837 (if CX is too large the routine returns with CF=1)
839 This routine performs final cleanup, then performs a sequence
840 of copies, and jumps to a specified entry point.
841 This is similar to function 0012h but allow more control over
842 the initial register state; see that function for the meaning of
843 ES:DI and CX.
845 DS:SI points to the initial register file, which is a structure
846 in the following format (available in <syslinux/bootrm.h>;
847 note that this is a completely different structure from the
848 com32sys_t structure described at the top of this document!):
850 struct syslinux_rm_regs {
851 uint16_t es; /* Offset 0 */
852 uint16_t _unused_cs; /* Offset 2 */
853 uint16_t ds; /* Offset 4 */
854 uint16_t ss; /* Offset 6 */
855 uint16_t fs; /* Offset 8 */
856 uint16_t gs; /* Offset 10 */
858 reg32_t eax; /* Offset 12 */
859 reg32_t ecx; /* Offset 16 */
860 reg32_t edx; /* Offset 20 */
861 reg32_t ebx; /* Offset 24 */
862 reg32_t esp; /* Offset 28 */
863 reg32_t ebp; /* Offset 32 */
864 reg32_t esi; /* Offset 36 */
865 reg32_t edi; /* Offset 40 */
867 uint16_t ip; /* Offset 44 */
868 uint16_t cs; /* Offset 46 */
869 };
871 Interrupts are off and DF=0 on entry.
874 AX=001Ch [3.60] Get pointer to auxilliary data vector
875 Input: AX 001Ch
876 Output: ES:BX Auxilliary data vector
877 CX Size of the ADV (currently 500 bytes)
879 The auxillary data vector is a tagged data structure used
880 to carry a small amount of information (up to 500 bytes) from
881 one boot to another.
884 AX=001Dh [3.60] Write auxilliary data vector
885 Input: AX 001Dh
886 Output: None
888 Write the auxilliary data vector back to disk. Returns
889 failure for non-disk-based derivatives unless the "auxdata"
890 configuration command is used to specify a disk location
891 (not yet implemented.)
893 In a future version, PXELINUX may end up attempting to save
894 the ADV on the server via TFTP write.