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 ++++ COM32R file format ++++
56 A COM32R file is a raw binary file containing 32-bit code. It should
57 be self-relocating, as it will be loaded by the Syslinux core at any
58 4K aligned address. 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 A COM32R program must start with the byte sequence B8 FE 4C CD 21 (mov
65 eax,21cd4cfeh) as a magic number.
67 The COM32R format replaces the earlier COM32 format, which was linked
68 to a fixed address (0x101000).
70 A COM32R file should have extension ".c32".
72 On startup, CS will be set up as a flat 32-bit code segment, and DS ==
73 ES == SS will be set up as the equivalent flat 32-bit data segment.
74 FS and GS are reserved for future use and are currently initialized to
75 zero. A COM32R image should not assume any particular values of
78 ESP is set up at the end of available memory and also serves as
79 notification to the program how much memory is available.
81 The following arguments are passed to the program on the stack:
84 [ESP] dword Return (termination) address
85 [ESP+4] dword Number of additional arguments (currently 7)
86 [ESP+8] dword Pointer to the command line arguments (null-terminated string)
87 [ESP+12] dword Pointer to INT call helper function
88 [ESP+16] dword Pointer to low memory bounce buffer
89 [ESP+20] dword Size of low memory bounce buffer
90 [ESP+24] dword Pointer to FAR call helper function (new in 2.05)
91 [ESP+28] dword Pointer to CDECL helper function (new in 3.54)
92 [ESP+32] dword Amount of memory controlled by the Syslinux core (new in 3.74)
93 [ESP+36] dword Pointer to protected-mode functions (new in 4.00)
95 The libcom32 startup code loads this into a structure named __com32,
98 extern struct com32_sys_args {
101 void __cdecl(*cs_intcall)(uint8_t, const com32sys_t *, com32sys_t *);
103 uint32_t cs_bounce_size;
104 void __cdecl(*cs_farcall)(uint32_t, const com32sys_t *, com32sys_t *);
105 int __cdecl(*cs_cfarcall)(uint32_t, const void *, uint32_t);
107 struct com32_pmapi *cs_pm;
110 The intcall helper function can be used to issue BIOS or Syslinux API
111 calls, and takes the interrupt number as first argument. The second
112 argument is a pointer to the input register definition, an instance of
113 the following structure (available in <com32.h>):
122 uint16_t gs; /* Offset 0 */
123 uint16_t fs; /* Offset 2 */
124 uint16_t es; /* Offset 4 */
125 uint16_t ds; /* Offset 6 */
127 reg32_t edi; /* Offset 8 */
128 reg32_t esi; /* Offset 12 */
129 reg32_t ebp; /* Offset 16 */
130 reg32_t _unused_esp; /* Offset 20 */
131 reg32_t ebx; /* Offset 24 */
132 reg32_t edx; /* Offset 28 */
133 reg32_t ecx; /* Offset 32 */
134 reg32_t eax; /* Offset 36 */
136 reg32_t eflags; /* Offset 40 */
139 The third argument is a pointer to the output register definition, an
140 instance of the same structure. The third argument can also be zero
143 Since BIOS or Syslinux API calls can generally only manipulate data
144 below address 0x100000, a "bounce buffer" in low memory, at least 64K
145 in size, is available, to copy data in and out.
147 The farcall helper function behaves similarly, but takes as its first
148 argument the CS:IP (in the form (CS << 16) + IP) of procedure to be
149 invoked via a FAR CALL.
151 The cfarcall helper function takes (CS << 16)+IP, a pointer to a stack
152 frame, a size of that stack frame, and returns the return value of EAX
153 (which may need to be appropriate truncated by the user.)
155 Starting in version 4.00, some of these API calls are available as
156 protected-mode function calls, using the regparm(3) calling convention
157 (the first three argumetns in EAX, EDX, ECX; the rest on the stack.)
158 Those functions are defined in struct com32_pmapi, defined in
162 ++++ SYSLINUX API CALLS +++
164 Syslinux provides the following API calls. Syslinux 1.xx only
165 supported INT 20h - terminate program. [] indicates the first version
166 of Syslinux which supported this feature (correctly.)
168 NOTE: Most of the API functionality is still experimental. Expect to
172 ++++ DOS-COMPATIBLE API CALLS ++++
174 INT 20h [1.48] Terminate program
175 INT 21h AH=00h [2.00] Terminate program
176 INT 21h AH=4Ch [2.00] Terminate program
178 All of these terminate the program.
181 INT 21h AH=01h [2.01] Get Key with Echo
183 Reads a key from the console input, with echo to the console
184 output. The read character is returned in AL. Extended
185 characters received from the keyboard are returned as NUL (00h)
186 + the extended character code.
189 INT 21h AH=02h [2.01] Write Character
191 Writes a character in DL to the console (video and serial)
195 INT 21h AH=04h [2.01] Write Character to Serial Port
197 Writes a character in DL to the serial console output
198 (if enabled.) If no serial port is configured, this routine
202 INT 21h AH=08h [2.09] Get Key without Echo
204 Reads a key fron the console input, without echoing it to the
205 console output. The read character is returned in AL.
208 INT 21h AH=09h [2.01] Write DOS String to Console
210 Writes a DOS $-terminated string in DS:DX to the console.
213 INT 21h AH=0Bh [2.00] Check Keyboard
215 Returns AL=FFh if there is a keystroke waiting (which can then
216 be read with INT 21h, AH=01h or AH=08h), otherwise AL=00h.
219 INT 21h AH=30h [2.00] Check DOS Version
221 This function returns AX=BX=CX=DX=0, corresponding to a
222 hypothetical "DOS 0.0", but the high parts of EAX-EBX-ECX-EDX
225 EAX=59530000h EBX=4C530000h ECX=4E490000h EDX=58550000h
227 This function can thus be used to distinguish running on
228 Syslinux from running on DOS.
231 ++++ SYSLINUX-SPECIFIC API CALLS ++++
233 Syslinux-specific API calls are executed using INT 22h, with a
234 function number in AX. INT 22h is used by DOS for internal purposes;
235 do not execute INT 22h under DOS.
237 DOS-compatible function INT 21h, AH=30h can be used to detect if the
238 Syslinux API calls are available.
240 Any register not specifically listed as modified is preserved;
241 however, future versions of Syslinux may add additional output
242 registers to existing calls.
244 All calls return CF=0 on success, CF=1 on failure. The noted outputs
245 apply if CF=0 only unless otherwise noted. All calls clobber the
246 arithmetric flags (CF, PF, AF, ZF, SF and OF) but leave all other
247 flags unchanged unless otherwise noted.
250 AX=0001h [2.00] Get Version
253 Output: AX number of INT 22h API functions available
254 CH Syslinux major version number
255 CL Syslinux minor version number
256 DL Syslinux derivative ID (e.g. 32h = PXELINUX)
257 ES:SI Syslinux version string
258 ES:DI Syslinux copyright string
260 This API call returns the Syslinux version and API
264 AX=0002h [2.01] Write String
267 ES:BX null-terminated string
270 Writes a null-terminated string on the console.
273 AX=0003h [2.01] Run command
276 ES:BX null-terminated command string
277 Output: Does not return
279 This API call terminates the program and executes the command
280 string as if the user had entered it at the Syslinux command
281 line. This API call does not return.
284 AX=0004h [2.01] Run default command
287 Output: Does not return
289 This API call terminates the program and executes the default
290 command string as if the user had pressed Enter alone on the
291 Syslinux command line. This API call does not return.
294 AX=0005h [2.00] Force text mode
299 If the screen was in graphics mode (due to displaying a splash
300 screen using the <Ctrl-X> command in a message file, or
301 similar), return to text mode.
304 AX=0006h [2.08] Open file
307 ES:SI null-terminated filename
308 Output: SI file handle
309 EAX length of file in bytes, or -1
312 Open a file for reading. The exact syntax of the filenames
313 allowed depends on the particular Syslinux derivative.
315 The Syslinux file system is block-oriented. The size of a
316 block will always be a power of two and no greater than 16K.
318 Note: Syslinux considers a zero-length file to be nonexistent.
320 In 3.70 or later, EAX can contain -1 indicating that the file
325 int cs_pm->open_file(const char *filename, struct com32_filedata *data)
327 filename - null-terminated filename
328 data - pointer to a file data buffer
330 Returns the file handle, or -1 on failure.
331 The file data buffer contains block size and file size.
334 AX=0007h [2.08] Read file
339 CX number of blocks to read
340 Output: SI file handle, or 0 if EOF was reached
341 ECX number of bytes read [3.70]
343 Read blocks from a file. Note that the file handle that is
344 returned in SI may not be the same value that was passed in.
346 If end of file was reached (SI=0), the file was automatically
349 In 3.70 or later, ECX returns the number of bytes read. This
350 will always be a multiple of the block size unless EOF is
353 The address of the buffer (ES:BX) should be at least 512-byte
354 aligned. Syslinux guarantees at least this alignment for the
355 COMBOOT load segment or the COM32 bounce buffer.
357 Keep in mind that a "file" may be a TFTP connection, and that
358 leaving a file open for an extended period of time may result
361 WARNING: Calling this function with an invalid file handle
362 will probably crash the system.
366 size_t cs_pm->read_file(uint16_t *handle, void *buf, size_t blocks)
368 handle - file handle (input and output, set to zero on end of file)
369 buf - buffer to write to
370 blocks - number of blocks to read
372 Returns number of bytes read, or 0 on failure.
375 AX=0008h [2.08] Close file
381 Close a file before reaching the end of file.
383 WARNING: Calling this function with an invalid file handle
384 will probably crash the system.
388 void cs_pm->close_file(uint16_t handle)
390 handle - file handle to close
393 AX=0009h [2.00] Call PXE Stack [PXELINUX ONLY]
396 BX PXE function number
397 ES:DI PXE parameter structure buffer
398 Output: AX PXE return status code
400 Invoke an arbitrary PXE stack function. On SYSLINUX/ISOLINUX,
401 this function returns with an error (CF=1) and no action is
402 taken. On PXELINUX, this function always returns with CF=0
403 indicating that the PXE stack was successfully invoked; check
404 the status code in AX and in the first word of the data buffer
405 to determine if the PXE call succeeded or not.
407 The PXE stack will have the UDP stack OPEN; if you change that
408 you cannot call any of the file-related API functions, and
409 must restore UDP OPEN before returning to PXELINUX.
411 PXELINUX reserves UDP port numbers from 49152 to 65535 for its
412 own use; port numbers below that range is available.
415 AX=000Ah [2.00] Get Derivative-Specific Information
419 CL 9 (to get a valid return in CL for all versions)
420 Output: AL 31h (SYSLINUX), 34h (EXTLINUX)
422 CL sector size as a power of 2 (9 = 512 bytes) [3.35]
423 ES:BX pointer to partition table entry (if DL >= 80h)
424 FS:SI pointer to initial ES:DI value [3.53]
426 Note: This function was broken in EXTLINUX 3.00-3.02.
428 On boot, ES:DI is supposed to point to the BIOS $PnP
429 structure, although in practice most operating systems
430 will search for it in memory. However, preserving
431 this while chainloading is probably a good idea.
433 Note that FS:SI is a pointer to a memory location
434 containing the original ES:DI value, not the value
440 Output: AL 32h (PXELINUX)
441 DX PXE API version detected (DH=major, DL=minor)
442 ECX Local IP number (network byte order) [3.85]
443 ES:BX pointer to PXENV+ or !PXE structure
444 FS:SI pointer to original stack with invocation record
446 Note: DX notes the API version detected by PXELINUX,
447 which may be more conservative than the actual version
448 available. For exact information examine the API
449 version entry in the PXENV+ structure, or the API
450 version entries in the ROMID structures pointed from
453 PXELINUX will use, and provide, the !PXE structure
454 over the PXENV+ structure. Examine the structure
455 signature to determine which particular structure was
458 The FS:SI pointer points to the top of the original stack
459 provided by the PXE stack, with the following values
460 pushed at the time PXELINUX is started:
462 [fs:si+0] GS <- top of stack
475 [fs:si+44] PXE return IP <- t.o.s. when PXELINUX invoked
476 [fs:si+46] PXE return CS
481 Output: AL 33h (ISOLINUX)
483 CL 11 (sector size as a power of 2) [3.35]
486 1 = Hybrid (hard disk), CBIOS mode
487 2 = Hybrid (hard disk), EBIOS mode
488 ES:BX pointer to El Torito spec packet
489 FS:SI pointer to initial ES:DI value [3.53]
491 Note: Some very broken El Torito implementations do
492 not provide the spec packet information. If so, ES:BX
493 may point to all zeroes or to garbage. Call INT 13h,
494 AX=4B01h to obtain the spec packet directly from the
497 This call gives information specific to a particular Syslinux
498 derivative. The value returned in AL is the same as is
499 returned in DL by INT 22h AX=0001h.
502 AX=000Bh [2.00] Get Serial Console Configuration
505 Output: DX serial port I/O base (e.g. 3F8h = COM1...)
506 CX baud rate divisor (1 = 115200 bps, 2 = 57600 bps...)
507 BX flow control configuration bits (see syslinux.txt)
508 -> bit 15 is set if the video console is disabled
510 If no serial port is configured, DX will be set to 0 and the
511 other registers are undefined.
514 AX=000Ch [2.00] Perform final cleanup
516 DX derivative-specific flags (0000h = clean up all)
519 This routine performs any "final cleanup" the boot loader
520 would normally perform before loading a kernel, such as
521 unloading the PXE stack in the case of PXELINUX. AFTER
522 INVOKING THIS CALL, NO OTHER API CALLS MAY BE INVOKED, NOR MAY
523 THE PROGRAM TERMINATE AND RETURN TO THE BOOT LOADER. This
524 call basically tells the boot loader "get out of the way, I'll
525 handle it from here."
527 For COM32 images, the boot loader will continue to provide
528 interrupt and BIOS call thunking services as long its memory
529 areas (0x0800-0xffff, 0x100000-0x100fff) are not overwritten.
530 MAKE SURE TO DISABLE INTERRUPTS, AND INSTALL NEW GDT AND IDTS
531 BEFORE OVERWRITING THESE MEMORY AREAS.
533 The permissible values for DX is an OR of these values:
535 SYSLINUX: 0000h Normal cleanup
537 PXELINUX: 0000h Normal cleanup
538 0003h Keep UNDI and PXE stacks loaded
540 ISOLINUX: 0000h Normal cleanup
542 EXTLINUX: 0000h Normal cleanup
544 All other values are undefined, and may have different
545 meanings in future versions of Syslinux.
548 AX=000Dh [2.08] Cleanup and replace bootstrap code
550 DX derivative-specific flags (see previous function)
551 EDI bootstrap code (linear address, can be in high memory)
552 ECX bootstrap code length in bytes (must fit in low mem)
553 EBX(!) initial value of EDX after bootstrap
554 ESI initial value of ESI after bootstrap
555 DS initial value of DS after bootstrap
556 Output: Does not return
558 This routine performs final cleanup, then takes a piece of
559 code, copies it over the primary bootstrap at address 7C00h,
560 and jumps to it. This can be used to chainload boot sectors,
561 MBRs, bootstraps, etc.
563 Normal boot sectors expect DL to contain the drive number,
564 and, for hard drives (DL >= 80h) DS:SI to contain a pointer to
565 the 16-byte partition table entry. The memory between
566 600h-7FFh is available to put the partition table entry in.
568 For PXELINUX, if the PXE stack is not unloaded, all registers
569 (except DS, ESI and EDX) and the stack will be set up as they
570 were set up by the PXE ROM.
573 AX=000Eh [2.11] Get configuration file name
575 Output: ES:BX null-terminated file name string
577 Returns the name of the configuration file. Note that it is
578 possible that the configuration file doesn't actually exist.
581 AX=000Fh [3.00] Get IPAPPEND strings [PXELINUX]
583 Output: CX number of strings (currently 2)
584 ES:BX pointer to an array of NEAR pointers in
585 the same segment, one for each of the above
588 Returns the same strings that the "ipappend" option would have
589 added to the command line, one for each bit of the "ipappend"
590 flag value, so entry 0 is the "ip=" string and entry 1 is the
594 AX=0010h [3.00] Resolve hostname [PXELINUX]
596 ES:BX pointer to null-terminated hostname
597 Output: EAX IP address of hostname (zero if not found)
599 Queries the DNS server(s) for a specific hostname. If the
600 hostname does not contain a dot (.), the local domain name
601 is automatically appended.
603 This function only return CF=1 if the function is not
604 supported. If the function is supported, but the hostname did
605 not resolve, it returns with CF=0, EAX=0.
607 The IP address is returned in network byte order, i.e. if the
608 IP address is 1.2.3.4, EAX will contain 0x04030201. Note that
609 all uses of IP addresses in PXE are also in network byte order.
612 AX=0011h [3.05] Obsoleted in 3.80
615 AX=0012h [3.50] Cleanup, shuffle and boot
617 DX derivative-specific flags (see function 000Ch)
618 ES:DI shuffle descriptor list (must be in low memory)
619 CX number of shuffle descriptors
620 EBX(!) initial value of EDX after bootstrap
621 ESI initial value of ESI after bootstrap
622 DS initial value of DS after bootstrap
623 EBP CS:IP of routine to jump to
624 Output: Does not return
625 (if CX is too large the routine returns with CF=1)
627 This routine performs final cleanup, then performs a sequence
628 of copies, and jumps to a specified real mode entry point.
629 This is a more general version of function 000Dh, which can
630 also be used to load other types of programs.
632 The copies must not touch memory below address 7C00h.
634 ES:DI points to a list of CX descriptors each of the form:
637 0 dword destination address
638 4 dword source address
639 8 dword length in bytes
641 The copies are overlap-safe, like memmove().
643 Starting in version 3.50, if the source address is -1
644 (FFFFFFFFh) then the block specified by the destination
645 address and the length is set to all zero.
647 Starting in version 3.50, if the destination address is -1
648 (FFFFFFFFh) then the data block is loaded as a new set of
649 descriptors, and processing is continued (and unprocessed
650 descriptors are lost, this is thus typically only used as the
651 last descriptor in a block.) The block must still fit in the
652 internal descriptor buffer (see function 0011h), but can, of
653 course, itself chain another block.
656 Normal boot sectors expect DL to contain the drive number,
657 and, for hard drives (DL >= 80h) DS:SI to contain a pointer to
658 the 16-byte partition table entry. The memory between
659 600h-7FFh is available to put the partition table entry in.
661 For PXELINUX, if the PXE stack is not unloaded, all registers
662 (except DS, ESI and EDX) and the stack will be set up as they
663 were set up by the PXE ROM.
665 This interface was probably broken before version 3.50.
668 AX=0013h [3.08] Idle loop call
672 Call this routine while sitting in an idle loop. It performs
673 any periodic activities required by the filesystem code. At
674 the moment, this is a no-op on all derivatives except
675 PXELINUX, where it executes PXE calls to answer ARP queries.
677 Starting with version 3.10, this API call harmlessly returns
678 failure (CF=1) if invoked on a platform which does not need
679 idle calls. Additionally, it's safe to call this API call on
680 previous Syslinux versions (2.00 or later); it will just
681 harmlessly fail. Thus, if this call returns failure (CF=1),
682 it means that there is no technical reason to call this
683 function again, although doing so is of course safe.
686 AX=0014h [3.10] Local boot [PXELINUX, ISOLINUX]
688 DX Local boot parameter
689 Output: Does not return
691 This function invokes the equivalent of the "localboot"
692 configuration file option. The parameter in DX is the same
693 parameter as would be entered after "localboot" in the
694 configuration file; this parameter is derivative-specific --
695 see syslinux.txt for the definition.
698 AX=0015h [3.10] Get feature flags
700 Output: ES:BX pointer to flags in memory
701 CX number of flag bytes
703 This function reports whether or not this Syslinux version and
704 derivative supports specific features. Keep in mind that
705 future versions might have more bits; remember to treat any
706 bits beyond the end of the array (as defined by the value in
709 Currently the following feature flag is defined:
712 ----------------------------------------------------
713 0 0 Local boot (AX=0014h) supported
714 1 Idle loop call (AX=0013h) is a no-op
716 All other flags are reserved.
719 AX=0016h [3.10] Run kernel image
721 DS:SI Filename of kernel image (zero-terminated string)
722 ES:BX Command line (zero-terminated string)
723 ECX IPAPPEND flags [PXELINUX]
724 EDX Type of file (since 3.50)
725 Output: Does not return if successful; returns with CF=1 if
726 the kernel image is not found.
728 This function is similiar to AX=0003h Run command, except that
729 the filename and command line are treated as if specified in a
730 KERNEL and APPEND statement of a LABEL statement, which means:
732 - The filename has to be exact; no variants are tried;
733 - No global APPEND statement is applied;
734 - ALLOWOPTIONS and IMPLICIT statements in the configuration
735 file do not apply. It is therefore important that the
736 COMBOOT module doesn't allow the end user to violate the
737 intent of the administrator.
739 Additionally, this function returns with a failure if the file
740 doesn't exist, instead of returning to the command line. (It
741 may still return to the command line if the image is somehow
744 The file types are defined as follows:
747 EDX Config Extensions Type of file
748 0 KERNEL Determined by filename extension
749 1 LINUX none Linux kernel image
750 2 BOOT .bs .bin Bootstrap program
751 3 BSS .bss Boot sector with patch [SYSLINUX]
752 4 PXE .0 PXE Network Bootstrap Prog [PXELINUX]
753 5 FDIMAGE .img Floppy disk image [ISOLINUX]
754 6 COMBOOT .com .cbt 16-bit COMBOOT program
755 7 COM32 .c32 COM32 program
756 8 CONFIG Configuration file
759 AX=0017h [3.30] Report video mode change
763 Bit 1: non-default mode
765 Bit 3: text functions not supported
766 CX For graphics modes, pixel columns
767 DX For graphics modes, pixel rows
770 This function is used to report video mode changes to
771 Syslinux. It does NOT actually change the video mode, but
772 rather, allows Syslinux to take appropriate action in response
773 to a video mode change. Modes that cannot be exited either
774 with the conventional BIOS mode set command (INT 10h, AH=00h)
775 or the VESA VBE mode set command (INT 10h, AX=4F02h) should
778 This function returns with a failure if BX contains any bits
779 which are undefined in the current version of Syslinux.
781 The following bits in BX are currently defined:
785 Indicates that the mode is a graphics mode, as opposed
788 Bit 1: non-standard mode
790 A non-standard mode is any mode except text mode and
791 graphics mode 0012h (VGA 640x480, 16 color.)
795 This mode is a VESA mode, and has to be exited with
796 the VESA VBE API (INT 10h, AX=4F02h) as opposed to the
797 conventional BIOS API (INT 10h, AH=00h).
799 Bit 3: Text functions not supported
801 This indicates that the BIOS text output functions
802 (INT 10h, AH=02h, 03h, 06h, 09h, 0Eh, 11h) don't work.
803 If this bit is set, Syslinux will reset the mode
804 before printing any characters on the screen.
806 This is common for VESA modes.
809 AX=0018h [3.30] Query custom font
811 Output: AL Height of custom font in scan lines, or zero
812 ES:BX Pointer to custom font in memory
814 This call queries if a custom display font has been loaded via
815 the "font" configuration file command. If no custom font has
816 been loaded, AL contains zero.
819 AX=0019h [3.50] Read disk [SYSLINUX, ISOLINUX, EXTLINUX]
822 ESI Reserved - MUST BE ZERO
823 EDI Reserved - MUST BE ZERO
828 Read disk blocks from the active filesystem (partition); for
829 disks, sector number zero is the boot sector. For ISOLINUX,
830 this call reads the CD-ROM.
832 For compatiblity with all systems, the buffer should
833 *neither* cross 64K boundaries, *nor* wrap around the segment.
835 This routine reports "boot failed" (and does not return) on
838 Note: for ISOLINUX in hybrid mode, this call uses simulated
839 2048-byte CD-ROM sector numbers.
842 AX=001Ah [3.50] Obsoleted in 3.80
845 AX=001Bh [3.50] Obsoleted in 3.80
848 AX=001Ch [3.60] Get pointer to auxilliary data vector
850 Output: ES:BX Auxilliary data vector
851 CX Size of the ADV (currently 500 bytes)
853 The auxillary data vector is a tagged data structure used
854 to carry a small amount of information (up to 500 bytes) from
858 AX=001Dh [3.60] Write auxilliary data vector
862 Write the auxilliary data vector back to disk. Returns
863 failure for non-disk-based derivatives unless the "auxdata"
864 configuration command is used to specify a disk location
865 (not yet implemented.)
867 In a future version, PXELINUX may end up attempting to save
868 the ADV on the server via TFTP write.
871 AX=001Eh [3.74] Keyboard remapping table
873 DX 0000h - all other values reserved
874 Output: AX format version (1)
875 CX length in bytes (256)
876 ES:BX pointer to keyboard table
878 This call queries the keyboard remapping table. For the current
879 version, the format code is always 1 and the length is always
880 256. This version can be updated simply by overwriting the version
881 in memory; this may not be true in the future.
884 AX=001Fh [3.74] Get current working directory
886 Output: ES:BX null-terminated directory name string
888 Returns the current working directory.
891 AX=0020h [3.74] Obsoleted in 4.00
892 AX=0021h [3.74] Obsoleted in 4.00
893 AX=0022h [3.74] Obsoleted in 4.00
895 These three functions provided opendir/readdir/closedir
896 functionality in the late 3.xx series. They have been
897 replaced by the protected-mode interface.
900 AX=0023h [3.80] Get shuffler parameters
902 Output: CX size of shuffler "safe area" in bytes
903 Other registers reserved for future use
905 This call gives the size of the required shuffler "safe area",
906 in bytes; for call 0024h. In the future, it may provide
907 additional parameters.
910 AX=0024h [3.80] Cleanup, shuffle and boot, raw version
912 DX derivative-specific flags (see function 000Ch)
913 EDI shuffle descriptor list safe area
914 ESI shuffle descriptor list source
915 ECX byte count of shuffle descriptor list
916 Output: Does not return
918 This routine performs final cleanup, then performs a sequence
919 of copies, and jumps to a specified real mode entry point.
920 This is a more general version of function 000Dh, which can
921 also be used to load other types of programs.
923 Unlike previous obsolete versions of this function, there are
924 no restrictions that copies must not touch memory below
925 address 7C00h. Either the shuffle descriptor list or the safe
926 area (or both) may be located in high memory.
928 ESI points to a list of descriptors each of the form:
931 0 dword destination address
932 4 dword source address (-1 = zero)
933 8 dword length in bytes (0 = end of list)
935 The copies are overlap-safe, like memmove().
937 Before actually executing the move list, the list is moved to
938 the address specified in EDI. The caller is responsibe to
939 ensure that the moved descriptor list plus a "safe area"
940 immediately afterwards (the size of which is specified by
941 function 0023h) is not disturbed by the copy sequence. It is,
942 however, safe to overwrite descriptors already consumed.
944 If the source address is -1 (FFFFFFFFh) then the block
945 specified by the destination address and the length is set to
948 The list is terminated by an entry with length 0. For that
949 entry, the destination is used as an entry point, and the
950 source represents the type of entry point:
952 0 16-bit protected mode (dst is CS.base)
953 1 Flat 32-bit protected mode (dst is EIP)
955 This routine does not set up any GPR register state
956 whatsoever, including stack. It is the responsibility of the
957 caller to make sure the entry point provided sets up any
960 For mode 0 (16-bit real mode), EAX will contain CR0 with bit 0
961 masked out, suitable for loading into CR0 to immediately enter
962 real mode. Note: if real-mode entry is planned,
963 (CS.base & 0xfff0000f) should == 0 for compatibility with KVM,
964 and possibly other virtualization solutions.
966 In both mode 0 and mode 1, the data segments will be loaded
967 with read/write data segments, matching the respective code
968 segment. For mode 0, B=0 and the limits will be 64K, for mode
969 1, B=1 and the limits will be 4 GB.
972 ++++ 32-BIT ONLY API CALLS ++++
974 void *pm_cs->lmalloc(size_t bytes)
976 Allocate a buffer in low memory (below 1 MB).
979 void pm_cs->lfree(void *ptr)
981 Free a buffer allocated with pm_cs->lmalloc().
984 DIR *pm_cs->opendir(const char *pathname)
989 struct dirent *pm_cs->readdir(DIR *dir)
991 Read an entry from a directory. The entry is returned in a
995 int pm_cs->closedir(DIR *dir)