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
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
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
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:
81 [ESP] dword Return (termination) address
82 [ESP+4] dword Number of additional arguments (currently 8)
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)
89 [ESP+32] dword Amount of memory controlled by the Syslinux core (new in 3.74)
90 [ESP+36] dword Pointer to the filename of the com32 module (new in 3.86)
92 The intcall helper function can be used to issue BIOS or Syslinux API
93 calls, and takes the interrupt number as first argument. The second
94 argument is a pointer to the input register definition, an instance of
95 the following structure (available in <com32.h>):
104 uint16_t gs; /* Offset 0 */
105 uint16_t fs; /* Offset 2 */
106 uint16_t es; /* Offset 4 */
107 uint16_t ds; /* Offset 6 */
109 reg32_t edi; /* Offset 8 */
110 reg32_t esi; /* Offset 12 */
111 reg32_t ebp; /* Offset 16 */
112 reg32_t _unused_esp; /* Offset 20 */
113 reg32_t ebx; /* Offset 24 */
114 reg32_t edx; /* Offset 28 */
115 reg32_t ecx; /* Offset 32 */
116 reg32_t eax; /* Offset 36 */
118 reg32_t eflags; /* Offset 40 */
121 The third argument is a pointer to the output register definition, an
122 instance of the same structure. The third argument can also be zero
125 Since BIOS or Syslinux API calls can generally only manipulate data
126 below address 0x100000, a "bounce buffer" in low memory, at least 64K
127 in size, is available, to copy data in and out.
129 The farcall helper function behaves similarly, but takes as its first
130 argument the CS:IP (in the form (CS << 16) + IP) of procedure to be
131 invoked via a FAR CALL.
133 The cfarcall helper function takes (CS << 16)+IP, a pointer to a stack
134 frame, a size of that stack frame, and returns the return value of EAX
135 (which may need to be appropriate truncated by the user.)
138 ++++ SYSLINUX API CALLS +++
140 Syslinux provides the following API calls. Syslinux 1.xx only
141 supported INT 20h - terminate program. [] indicates the first version
142 of Syslinux which supported this feature (correctly.)
144 NOTE: Most of the API functionality is still experimental. Expect to
148 ++++ DOS-COMPATIBLE API CALLS ++++
150 INT 20h [1.48] Terminate program
151 INT 21h AH=00h [2.00] Terminate program
152 INT 21h AH=4Ch [2.00] Terminate program
154 All of these terminate the program.
157 INT 21h AH=01h [2.01] Get Key with Echo
159 Reads a key from the console input, with echo to the console
160 output. The read character is returned in AL. Extended
161 characters received from the keyboard are returned as NUL (00h)
162 + the extended character code.
165 INT 21h AH=02h [2.01] Write Character
167 Writes a character in DL to the console (video and serial)
171 INT 21h AH=04h [2.01] Write Character to Serial Port
173 Writes a character in DL to the serial console output
174 (if enabled.) If no serial port is configured, this routine
178 INT 21h AH=08h [2.09] Get Key without Echo
180 Reads a key fron the console input, without echoing it to the
181 console output. The read character is returned in AL.
184 INT 21h AH=09h [2.01] Write DOS String to Console
186 Writes a DOS $-terminated string in DS:DX to the console.
189 INT 21h AH=0Bh [2.00] Check Keyboard
191 Returns AL=FFh if there is a keystroke waiting (which can then
192 be read with INT 21h, AH=01h or AH=08h), otherwise AL=00h.
195 INT 21h AH=30h [2.00] Check DOS Version
197 This function returns AX=BX=CX=DX=0, corresponding to a
198 hypothetical "DOS 0.0", but the high parts of EAX-EBX-ECX-EDX
201 EAX=59530000h EBX=4C530000h ECX=4E490000h EDX=58550000h
203 This function can thus be used to distinguish running on
204 Syslinux from running on DOS.
207 ++++ SYSLINUX-SPECIFIC API CALLS ++++
209 Syslinux-specific API calls are executed using INT 22h, with a
210 function number in AX. INT 22h is used by DOS for internal purposes;
211 do not execute INT 22h under DOS.
213 DOS-compatible function INT 21h, AH=30h can be used to detect if the
214 Syslinux API calls are available.
216 Any register not specifically listed as modified is preserved;
217 however, future versions of Syslinux may add additional output
218 registers to existing calls.
220 All calls return CF=0 on success, CF=1 on failure. The noted outputs
221 apply if CF=0 only unless otherwise noted. All calls clobber the
222 arithmetric flags (CF, PF, AF, ZF, SF and OF) but leave all other
223 flags unchanged unless otherwise noted.
226 AX=0001h [2.00] Get Version
229 Output: AX number of INT 22h API functions available
230 CH Syslinux major version number
231 CL Syslinux minor version number
232 DL Syslinux derivative ID (e.g. 32h = PXELINUX)
233 ES:SI Syslinux version string
234 ES:DI Syslinux copyright string
236 This API call returns the Syslinux version and API
239 Note: before version 3.86, the version string had a leading CR LF
240 and the copyright string had a leading space. The strings might
241 still contain trailing CR and/or LF.
244 AX=0002h [2.01] Write String
247 ES:BX null-terminated string
250 Writes a null-terminated string on the console.
253 AX=0003h [2.01] Run command
256 ES:BX null-terminated command string
257 Output: Does not return
259 This API call terminates the program and executes the command
260 string as if the user had entered it at the Syslinux command
261 line. This API call does not return.
264 AX=0004h [2.01] Run default command
267 Output: Does not return
269 This API call terminates the program and executes the default
270 command string as if the user had pressed Enter alone on the
271 Syslinux command line. This API call does not return.
274 AX=0005h [2.00] Force text mode
279 If the screen was in graphics mode (due to displaying a splash
280 screen using the <Ctrl-X> command in a message file, or
281 similar), return to text mode.
284 AX=0006h [2.08] Open file
287 ES:SI null-terminated filename
288 Output: SI file handle
289 EAX length of file in bytes, or -1
292 Open a file for reading. The exact syntax of the filenames
293 allowed depends on the particular Syslinux derivative.
295 The Syslinux file system is block-oriented. The size of a
296 block will always be a power of two and no greater than 16K.
298 Note: Syslinux considers a zero-length file to be nonexistent.
300 In 3.70 or later, EAX can contain -1 indicating that the file
304 AX=0007h [2.08] Read file
309 CX number of blocks to read
310 Output: SI file handle, or 0 if EOF was reached
311 ECX number of bytes read [3.70]
313 Read blocks from a file. Note that the file handle that is
314 returned in SI may not be the same value that was passed in.
316 If end of file was reached (SI=0), the file was automatically
319 In 3.70 or later, ECX returns the number of bytes read. This
320 will always be a multiple of the block size unless EOF is
323 The address of the buffer (ES:BX) should be at least 512-byte
324 aligned. Syslinux guarantees at least this alignment for the
325 COMBOOT load segment or the COM32 bounce buffer.
327 Keep in mind that a "file" may be a TFTP connection, and that
328 leaving a file open for an extended period of time may result
331 WARNING: Calling this function with an invalid file handle
332 will probably crash the system.
335 AX=0008h [2.08] Close file
341 Close a file before reaching the end of file.
343 WARNING: Calling this function with an invalid file handle
344 will probably crash the system.
347 AX=0009h [2.00] Call PXE Stack [PXELINUX ONLY]
350 BX PXE function number
351 ES:DI PXE parameter structure buffer
352 Output: AX PXE return status code
354 Invoke an arbitrary PXE stack function. On SYSLINUX/ISOLINUX,
355 this function returns with an error (CF=1) and no action is
356 taken. On PXELINUX, this function always returns with CF=0
357 indicating that the PXE stack was successfully invoked; check
358 the status code in AX and in the first word of the data buffer
359 to determine if the PXE call succeeded or not.
361 The PXE stack will have the UDP stack OPEN; if you change that
362 you cannot call any of the file-related API functions, and
363 must restore UDP OPEN before returning to PXELINUX.
365 PXELINUX reserves UDP port numbers from 49152 to 65535 for its
366 own use; port numbers below that range is available.
369 AX=000Ah [2.00] Get Derivative-Specific Information
373 CL 9 (to get a valid return in CL for all versions)
374 Output: AL 31h (SYSLINUX), 34h (EXTLINUX)
376 CL sector size as a power of 2 (9 = 512 bytes) [3.35]
377 ES:BX pointer to partition table entry (if DL >= 80h)
378 FS:SI pointer to initial ES:DI value [3.53]
380 Note: This function was broken in EXTLINUX 3.00-3.02.
382 On boot, ES:DI is supposed to point to the BIOS $PnP
383 structure, although in practice most operating systems
384 will search for it in memory. However, preserving
385 this while chainloading is probably a good idea.
387 Note that FS:SI is a pointer to a memory location
388 containing the original ES:DI value, not the value
394 Output: AL 32h (PXELINUX)
395 DX PXE API version detected (DH=major, DL=minor)
396 ECX Local IP number (network byte order) [3.85]
397 ES:BX pointer to PXENV+ or !PXE structure
398 FS:SI pointer to original stack with invocation record
400 Note: DX notes the API version detected by PXELINUX,
401 which may be more conservative than the actual version
402 available. For exact information examine the API
403 version entry in the PXENV+ structure, or the API
404 version entries in the ROMID structures pointed from
407 PXELINUX will use, and provide, the !PXE structure
408 over the PXENV+ structure. Examine the structure
409 signature to determine which particular structure was
412 The FS:SI pointer points to the top of the original stack
413 provided by the PXE stack, with the following values
414 pushed at the time PXELINUX is started:
416 [fs:si+0] GS <- top of stack
429 [fs:si+44] PXE return IP <- t.o.s. when PXELINUX invoked
430 [fs:si+46] PXE return CS
435 Output: AL 33h (ISOLINUX)
437 CL 11 (sector size as a power of 2) [3.35]
440 1 = Hybrid (hard disk), CBIOS mode
441 2 = Hybrid (hard disk), EBIOS mode
442 ES:BX pointer to El Torito spec packet
443 FS:SI pointer to initial ES:DI value [3.53]
445 Note: Some very broken El Torito implementations do
446 not provide the spec packet information. If so, ES:BX
447 may point to all zeroes or to garbage. Call INT 13h,
448 AX=4B01h to obtain the spec packet directly from the
451 This call gives information specific to a particular Syslinux
452 derivative. The value returned in AL is the same as is
453 returned in DL by INT 22h AX=0001h.
456 AX=000Bh [2.00] Get Serial Console Configuration
459 Output: DX serial port I/O base (e.g. 3F8h = COM1...)
460 CX baud rate divisor (1 = 115200 bps, 2 = 57600 bps...)
461 BX flow control configuration bits (see syslinux.txt)
462 -> bit 15 is set if the video console is disabled
464 If no serial port is configured, DX will be set to 0 and the
465 other registers are undefined.
468 AX=000Ch [2.00] Perform final cleanup
470 DX derivative-specific flags (0000h = clean up all)
473 This routine performs any "final cleanup" the boot loader
474 would normally perform before loading a kernel, such as
475 unloading the PXE stack in the case of PXELINUX. AFTER
476 INVOKING THIS CALL, NO OTHER API CALLS MAY BE INVOKED, NOR MAY
477 THE PROGRAM TERMINATE AND RETURN TO THE BOOT LOADER. This
478 call basically tells the boot loader "get out of the way, I'll
479 handle it from here."
481 For COM32 images, the boot loader will continue to provide
482 interrupt and BIOS call thunking services as long its memory
483 areas (0x0800-0xffff, 0x100000-0x100fff) are not overwritten.
484 MAKE SURE TO DISABLE INTERRUPTS, AND INSTALL NEW GDT AND IDTS
485 BEFORE OVERWRITING THESE MEMORY AREAS.
487 The permissible values for DX is an OR of these values:
489 SYSLINUX: 0000h Normal cleanup
491 PXELINUX: 0000h Normal cleanup
492 0003h Keep UNDI and PXE stacks loaded
494 ISOLINUX: 0000h Normal cleanup
496 EXTLINUX: 0000h Normal cleanup
498 All other values are undefined, and may have different
499 meanings in future versions of Syslinux.
502 AX=000Dh [2.08] Cleanup and replace bootstrap code
504 DX derivative-specific flags (see previous function)
505 EDI bootstrap code (linear address, can be in high memory)
506 ECX bootstrap code length in bytes (must fit in low mem)
507 EBX(!) initial value of EDX after bootstrap
508 ESI initial value of ESI after bootstrap
509 DS initial value of DS after bootstrap
510 Output: Does not return
512 This routine performs final cleanup, then takes a piece of
513 code, copies it over the primary bootstrap at address 7C00h,
514 and jumps to it. This can be used to chainload boot sectors,
515 MBRs, bootstraps, etc.
517 Normal boot sectors expect DL to contain the drive number,
518 and, for hard drives (DL >= 80h) DS:SI to contain a pointer to
519 the 16-byte partition table entry. The memory between
520 600h-7FFh is available to put the partition table entry in.
522 For PXELINUX, if the PXE stack is not unloaded, all registers
523 (except DS, ESI and EDX) and the stack will be set up as they
524 were set up by the PXE ROM.
527 AX=000Eh [2.11] Get configuration file name
529 Output: ES:BX null-terminated file name string
531 Returns the name of the configuration file. Note that it is
532 possible that the configuration file doesn't actually exist.
535 AX=000Fh [3.00] Get IPAPPEND strings [PXELINUX]
537 Output: CX number of strings (currently 2)
538 ES:BX pointer to an array of NEAR pointers in
539 the same segment, one for each of the above
542 Returns the same strings that the "ipappend" option would have
543 added to the command line, one for each bit of the "ipappend"
544 flag value, so entry 0 is the "ip=" string and entry 1 is the
548 AX=0010h [3.00] Resolve hostname [PXELINUX]
550 ES:BX pointer to null-terminated hostname
551 Output: EAX IP address of hostname (zero if not found)
553 Queries the DNS server(s) for a specific hostname. If the
554 hostname does not contain a dot (.), the local domain name
555 is automatically appended.
557 This function only return CF=1 if the function is not
558 supported. If the function is supported, but the hostname did
559 not resolve, it returns with CF=0, EAX=0.
561 The IP address is returned in network byte order, i.e. if the
562 IP address is 1.2.3.4, EAX will contain 0x04030201. Note that
563 all uses of IP addresses in PXE are also in network byte order.
566 AX=0011h [3.05] Obsoleted in 3.80
569 AX=0012h [3.50] Cleanup, shuffle and boot
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:
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
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]
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.txt for the definition.
652 AX=0015h [3.10] Get feature flags
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
663 Currently the following feature flag is defined:
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
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
698 The file types are defined as follows:
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
717 Bit 1: non-default mode
719 Bit 3: text functions not supported
720 CX For graphics modes, pixel columns
721 DX For graphics modes, pixel rows
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
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:
739 Indicates that the mode is a graphics mode, as opposed
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.)
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
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]
776 ESI Reserved - MUST BE ZERO
777 EDI Reserved - MUST BE ZERO
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
792 Note: for ISOLINUX in hybrid mode, this call uses simulated
793 2048-byte CD-ROM sector numbers.
796 AX=001Ah [3.50] Obsoleted in 3.80
799 AX=001Bh [3.50] Obsoleted in 3.80
802 AX=001Ch [3.60] Get pointer to auxilliary data vector
804 Output: ES:BX Auxilliary data vector
805 CX Size of the ADV (currently 500 bytes)
807 The auxillary data vector is a tagged data structure used
808 to carry a small amount of information (up to 500 bytes) from
812 AX=001Dh [3.60] Write auxilliary data vector
816 Write the auxilliary data vector back to disk. Returns
817 failure for non-disk-based derivatives unless the "auxdata"
818 configuration command is used to specify a disk location
819 (not yet implemented.)
821 In a future version, PXELINUX may end up attempting to save
822 the ADV on the server via TFTP write.
825 AX=001Eh [3.74] Keyboard remapping table
827 DX 0000h - all other values reserved
828 Output: AX format version (1)
829 CX length in bytes (256)
830 ES:BX pointer to keyboard table
832 This call queries the keyboard remapping table. For the current
833 version, the format code is always 1 and the length is always
834 256. This version can be updated simply by overwriting the version
835 in memory; this may not be true in the future.
838 AX=001Fh [3.74] Get current working directory
840 Output: ES:BX null-terminated directory name string
842 Returns the current working directory. For SYSLINUX, ISOLINUX,
843 and PXELINUX, this will be an absolute path. For EXTLINUX, it
844 currently returns "./".
847 AX=0020h [3.74] Open directory
849 ES:SI /-null-terminated directory name
850 Output: SI directory handle
853 Open a directory for reading. Directory name must have a trailing
854 "/" before the null (otherwise, you're looking for a file)(This
855 may change as this is a BETA call).
858 AX=0021h [3.74] Read directory
861 ES:DI buffer for file name
862 Output: DL Type of file
863 SI directory handle, or 0 if end of directory was reached
867 Read one filename from the directory, incrementing the
868 directory structure at SI as appropriate, storing the filename
869 into the buffer at ES:DI, and returning the type of the file
870 in DL, the file length in EAX, the inode/file number in EBX
871 and the updated directory handle.
874 AX=0022h [3.74] Close directory
882 AX=0023h [3.80] Get shuffler parameters
884 Output: CX size of shuffler "safe area" in bytes
885 Other registers reserved for future use
887 This call gives the size of the required shuffler "safe area",
888 in bytes; for call 0024h. In the future, it may provide
889 additional parameters.
892 AX=0024h [3.80] Cleanup, shuffle and boot, raw version
894 DX derivative-specific flags (see function 000Ch)
895 EDI shuffle descriptor list safe area
896 ESI shuffle descriptor list source
897 ECX byte count of shuffle descriptor list
898 Output: Does not return
900 This routine performs final cleanup, then performs a sequence
901 of copies, and jumps to a specified real mode entry point.
902 This is a more general version of function 000Dh, which can
903 also be used to load other types of programs.
905 Unlike previous obsolete versions of this function, there are
906 no restrictions that copies must not touch memory below
907 address 7C00h. Either the shuffle descriptor list or the safe
908 area (or both) may be located in high memory.
910 ESI points to a list of descriptors each of the form:
913 0 dword destination address
914 4 dword source address (-1 = zero)
915 8 dword length in bytes (0 = end of list)
917 The copies are overlap-safe, like memmove().
919 Before actually executing the move list, the list is moved to
920 the address specified in EDI. The caller is responsibe to
921 ensure that the moved descriptor list plus a "safe area"
922 immediately afterwards (the size of which is specified by
923 function 0023h) is not disturbed by the copy sequence. It is,
924 however, safe to overwrite descriptors already consumed.
926 If the source address is -1 (FFFFFFFFh) then the block
927 specified by the destination address and the length is set to
930 The list is terminated by an entry with length 0. For that
931 entry, the destination is used as an entry point, and the
932 source represents the type of entry point:
934 0 16-bit protected mode (dst is CS.base)
935 1 Flat 32-bit protected mode (dst is EIP)
937 This routine does not set up any GPR register state
938 whatsoever, including stack. It is the responsibility of the
939 caller to make sure the entry point provided sets up any
942 For mode 0 (16-bit real mode), EAX will contain CR0 with bit 0
943 masked out, suitable for loading into CR0 to immediately enter
944 real mode. Note: if real-mode entry is planned,
945 (CS.base & 0xfff0000f) should == 0 for compatibility with KVM,
946 and possibly other virtualization solutions.
948 In both mode 0 and mode 1, the data segments will be loaded
949 with read/write data segments, matching the respective code
950 segment. For mode 0, B=0 and the limits will be 64K, for mode
951 1, B=1 and the limits will be 4 GB.