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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 ++++ 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
76 segment selectors.
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:
83 Address Size Meaning
84 [ESP] dword Return (termination) address
85 [ESP+4] dword Number of additional arguments (currently 8)
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 the filename of the com32 module (new in 3.86)
94 [ESP+40] dword Pointer to protected-mode functions (new in 4.00)
96 The libcom32 startup code loads this into a structure named __com32,
97 defined in <com32.h>:
99 extern struct com32_sys_args {
100 uint32_t cs_sysargs;
101 char *cs_cmdline;
102 void __cdecl(*cs_intcall)(uint8_t, const com32sys_t *, com32sys_t *);
103 void *cs_bounce;
104 uint32_t cs_bounce_size;
105 void __cdecl(*cs_farcall)(uint32_t, const com32sys_t *, com32sys_t *);
106 int __cdecl(*cs_cfarcall)(uint32_t, const void *, uint32_t);
107 uint32_t cs_memsize;
108 const char *cs_name;
109 const struct com32_pmapi *cs_pm;
110 } __com32;
112 The intcall helper function can be used to issue BIOS or Syslinux API
113 calls, and takes the interrupt number as first argument. The second
114 argument is a pointer to the input register definition, an instance of
115 the following structure (available in <com32.h>):
117 typedef union {
118 uint32_t l;
119 uint16_t w[2];
120 uint8_t b[4];
121 } reg32_t;
123 typedef struct {
124 uint16_t gs; /* Offset 0 */
125 uint16_t fs; /* Offset 2 */
126 uint16_t es; /* Offset 4 */
127 uint16_t ds; /* Offset 6 */
129 reg32_t edi; /* Offset 8 */
130 reg32_t esi; /* Offset 12 */
131 reg32_t ebp; /* Offset 16 */
132 reg32_t _unused_esp; /* Offset 20 */
133 reg32_t ebx; /* Offset 24 */
134 reg32_t edx; /* Offset 28 */
135 reg32_t ecx; /* Offset 32 */
136 reg32_t eax; /* Offset 36 */
138 reg32_t eflags; /* Offset 40 */
139 } com32sys_t;
141 The third argument is a pointer to the output register definition, an
142 instance of the same structure. The third argument can also be zero
143 (NULL).
145 Since BIOS or Syslinux API calls can generally only manipulate data
146 below address 0x100000, a "bounce buffer" in low memory, at least 64K
147 in size, is available, to copy data in and out.
149 The farcall helper function behaves similarly, but takes as its first
150 argument the CS:IP (in the form (CS << 16) + IP) of procedure to be
151 invoked via a FAR CALL.
153 The cfarcall helper function takes (CS << 16)+IP, a pointer to a stack
154 frame, a size of that stack frame, and returns the return value of EAX
155 (which may need to be appropriate truncated by the user.)
157 Starting in version 4.00, some of these API calls are available as
158 protected-mode function calls, using the regparm(3) calling convention
159 (the first three argumetns in EAX, EDX, ECX; the rest on the stack.)
160 Those functions are defined in struct com32_pmapi, defined in
161 <syslinux/pmapi.h>.
164 ++++ SYSLINUX API CALLS +++
166 Syslinux provides the following API calls. Syslinux 1.xx only
167 supported INT 20h - terminate program. [] indicates the first version
168 of Syslinux which supported this feature (correctly.)
170 NOTE: Most of the API functionality is still experimental. Expect to
171 find bugs.
174 ++++ DOS-COMPATIBLE API CALLS ++++
176 INT 20h [1.48] Terminate program
177 INT 21h AH=00h [2.00] Terminate program
178 INT 21h AH=4Ch [2.00] Terminate program
180 All of these terminate the program.
183 INT 21h AH=01h [2.01] Get Key with Echo
185 Reads a key from the console input, with echo to the console
186 output. The read character is returned in AL. Extended
187 characters received from the keyboard are returned as NUL (00h)
188 + the extended character code.
191 INT 21h AH=02h [2.01] Write Character
193 Writes a character in DL to the console (video and serial)
194 output.
197 INT 21h AH=04h [2.01] Write Character to Serial Port
199 Writes a character in DL to the serial console output
200 (if enabled.) If no serial port is configured, this routine
201 does nothing.
204 INT 21h AH=08h [2.09] Get Key without Echo
206 Reads a key fron the console input, without echoing it to the
207 console output. The read character is returned in AL.
210 INT 21h AH=09h [2.01] Write DOS String to Console
212 Writes a DOS $-terminated string in DS:DX to the console.
215 INT 21h AH=0Bh [2.00] Check Keyboard
217 Returns AL=FFh if there is a keystroke waiting (which can then
218 be read with INT 21h, AH=01h or AH=08h), otherwise AL=00h.
221 INT 21h AH=30h [2.00] Check DOS Version
223 This function returns AX=BX=CX=DX=0, corresponding to a
224 hypothetical "DOS 0.0", but the high parts of EAX-EBX-ECX-EDX
225 spell "SYSLINUX":
227 EAX=59530000h EBX=4C530000h ECX=4E490000h EDX=58550000h
229 This function can thus be used to distinguish running on
230 Syslinux from running on DOS.
233 ++++ SYSLINUX-SPECIFIC API CALLS ++++
235 Syslinux-specific API calls are executed using INT 22h, with a
236 function number in AX. INT 22h is used by DOS for internal purposes;
237 do not execute INT 22h under DOS.
239 DOS-compatible function INT 21h, AH=30h can be used to detect if the
240 Syslinux API calls are available.
242 Any register not specifically listed as modified is preserved;
243 however, future versions of Syslinux may add additional output
244 registers to existing calls.
246 All calls return CF=0 on success, CF=1 on failure. The noted outputs
247 apply if CF=0 only unless otherwise noted. All calls clobber the
248 arithmetric flags (CF, PF, AF, ZF, SF and OF) but leave all other
249 flags unchanged unless otherwise noted.
252 AX=0001h [2.00] Get Version
254 Input: AX 0001h
255 Output: AX number of INT 22h API functions available
256 CH Syslinux major version number
257 CL Syslinux minor version number
258 DL Syslinux derivative ID (e.g. 32h = PXELINUX)
259 ES:SI Syslinux version string
260 ES:DI Syslinux copyright string
262 This API call returns the Syslinux version and API
263 information.
265 Note: before version 3.86, the version string had a leading CR LF
266 and the copyright string had a leading space. The strings might
267 still contain trailing CR and/or LF.
270 AX=0002h [2.01] Write String
272 Input: AX 0002h
273 ES:BX null-terminated string
274 Output: None
276 Writes a null-terminated string on the console.
279 AX=0003h [2.01] Run command
281 Input: AX 0003h
282 ES:BX null-terminated command string
283 Output: Does not return
285 This API call terminates the program and executes the command
286 string as if the user had entered it at the Syslinux command
287 line. This API call does not return.
290 AX=0004h [2.01] Run default command
292 Input: AX 0004h
293 Output: Does not return
295 This API call terminates the program and executes the default
296 command string as if the user had pressed Enter alone on the
297 Syslinux command line. This API call does not return.
300 AX=0005h [2.00] Force text mode
302 Input: AX 0005h
303 Output: None
305 If the screen was in graphics mode (due to displaying a splash
306 screen using the <Ctrl-X> command in a message file, or
307 similar), return to text mode.
310 AX=0006h [2.08] Open file
312 Input: AX 0006h
313 ES:SI null-terminated filename
314 Output: SI file handle
315 EAX length of file in bytes, or -1
316 CX file block size
318 Open a file for reading. The exact syntax of the filenames
319 allowed depends on the particular Syslinux derivative.
321 The Syslinux file system is block-oriented. The size of a
322 block will always be a power of two and no greater than 16K.
324 Note: Syslinux considers a zero-length file to be nonexistent.
326 In 3.70 or later, EAX can contain -1 indicating that the file
327 length is unknown.
329 32-BIT VERSION:
331 int cs_pm->open_file(const char *filename, struct com32_filedata *data)
333 filename - null-terminated filename
334 data - pointer to a file data buffer
336 Returns the file handle, or -1 on failure.
337 The file data buffer contains block size and file size.
340 AX=0007h [2.08] Read file
342 Input: AX 0007h
343 SI file handle
344 ES:BX buffer
345 CX number of blocks to read
346 Output: SI file handle, or 0 if EOF was reached
347 ECX number of bytes read [3.70]
349 Read blocks from a file. Note that the file handle that is
350 returned in SI may not be the same value that was passed in.
352 If end of file was reached (SI=0), the file was automatically
353 closed.
355 In 3.70 or later, ECX returns the number of bytes read. This
356 will always be a multiple of the block size unless EOF is
357 reached.
359 The address of the buffer (ES:BX) should be at least 512-byte
360 aligned. Syslinux guarantees at least this alignment for the
361 COMBOOT load segment or the COM32 bounce buffer.
363 Keep in mind that a "file" may be a TFTP connection, and that
364 leaving a file open for an extended period of time may result
365 in a timeout.
367 WARNING: Calling this function with an invalid file handle
368 will probably crash the system.
370 32-BIT VERSION:
372 size_t cs_pm->read_file(uint16_t *handle, void *buf, size_t blocks)
374 handle - file handle (input and output, set to zero on end of file)
375 buf - buffer to write to
376 blocks - number of blocks to read
378 Returns number of bytes read, or 0 on failure.
381 AX=0008h [2.08] Close file
383 Input: AX 0008h
384 SI file handle
385 Output: None
387 Close a file before reaching the end of file.
389 WARNING: Calling this function with an invalid file handle
390 will probably crash the system.
392 32-BIT VERSION:
394 void cs_pm->close_file(uint16_t handle)
396 handle - file handle to close
399 AX=0009h [2.00] Call PXE Stack [PXELINUX ONLY]
401 Input: AX 0009h
402 BX PXE function number
403 ES:DI PXE parameter structure buffer
404 Output: AX PXE return status code
406 Invoke an arbitrary PXE stack function. On SYSLINUX/ISOLINUX,
407 this function returns with an error (CF=1) and no action is
408 taken. On PXELINUX, this function always returns with CF=0
409 indicating that the PXE stack was successfully invoked; check
410 the status code in AX and in the first word of the data buffer
411 to determine if the PXE call succeeded or not.
413 The PXE stack will have the UDP stack OPEN; if you change that
414 you cannot call any of the file-related API functions, and
415 must restore UDP OPEN before returning to PXELINUX.
417 PXELINUX reserves UDP port numbers from 49152 to 65535 for its
418 own use; port numbers below that range is available.
421 AX=000Ah [2.00] Get Derivative-Specific Information
423 [SYSLINUX, EXTLINUX]
424 Input: AX 000Ah
425 CL 9 (to get a valid return in CL for all versions)
426 Output: AL 31h (SYSLINUX), 34h (EXTLINUX)
427 DL drive number
428 CL sector size as a power of 2 (9 = 512 bytes) [3.35]
429 ES:BX pointer to partition table entry (if DL >= 80h)
430 FS:SI pointer to initial ES:DI value [3.53]
432 Note: This function was broken in EXTLINUX 3.00-3.02.
434 On boot, ES:DI is supposed to point to the BIOS $PnP
435 structure, although in practice most operating systems
436 will search for it in memory. However, preserving
437 this while chainloading is probably a good idea.
439 Note that FS:SI is a pointer to a memory location
440 containing the original ES:DI value, not the value
441 itself.
444 [PXELINUX]
445 Input: AX 000Ah
446 Output: AL 32h (PXELINUX)
447 DX PXE API version detected (DH=major, DL=minor)
448 ECX Local IP number (network byte order) [3.85]
449 ES:BX pointer to PXENV+ or !PXE structure
450 FS:SI pointer to original stack with invocation record
451 GS:DI pointer to network information [4.00]
453 Note: DX notes the API version detected by PXELINUX,
454 which may be more conservative than the actual version
455 available. For exact information examine the API
456 version entry in the PXENV+ structure, or the API
457 version entries in the ROMID structures pointed from
458 the !PXE structure.
460 PXELINUX will use, and provide, the !PXE structure
461 over the PXENV+ structure. Examine the structure
462 signature to determine which particular structure was
463 provided.
465 The FS:SI pointer points to the top of the original stack
466 provided by the PXE stack, with the following values
467 pushed at the time PXELINUX is started:
469 [fs:si+0] GS <- top of stack
470 [fs:si+2] FS
471 [fs:si+4] ES
472 [fs:si+6] DS
473 [fs:si+8] EDI
474 [fs:si+12] ESI
475 [fs:si+16] EBP
476 [fs:si+20] -
477 [fs:si+24] EBX
478 [fs:si+28] EDX
479 [fs:si+32] ECX
480 [fs:si+36] EAX
481 [fs:si+40] EFLAGS
482 [fs:si+44] PXE return IP <- t.o.s. when PXELINUX invoked
483 [fs:si+46] PXE return CS
485 GS:DI points to a structure of the following form:
487 [gs:di+0] 4 - IPv4
488 [gs:di+4] My IP
489 [gs:di+8] Boot server IP
490 [gs:di+12] Gateway IP
491 [gs:di+16] Netmask
493 [ISOLINUX]
494 Input: AX 000Ah
495 Output: AL 33h (ISOLINUX)
496 DL drive number
497 CL 11 (sector size as a power of 2) [3.35]
498 CH mode [3.73]
499 0 = El Torito
500 1 = Hybrid (hard disk), CBIOS mode
501 2 = Hybrid (hard disk), EBIOS mode
502 ES:BX pointer to El Torito spec packet
503 FS:SI pointer to initial ES:DI value [3.53]
505 Note: Some very broken El Torito implementations do
506 not provide the spec packet information. If so, ES:BX
507 may point to all zeroes or to garbage. Call INT 13h,
508 AX=4B01h to obtain the spec packet directly from the
509 BIOS if necessary.
511 This call gives information specific to a particular Syslinux
512 derivative. The value returned in AL is the same as is
513 returned in DL by INT 22h AX=0001h.
516 AX=000Bh [2.00] Get Serial Console Configuration
518 Input: AX 000Bh
519 Output: DX serial port I/O base (e.g. 3F8h = COM1...)
520 CX baud rate divisor (1 = 115200 bps, 2 = 57600 bps...)
521 BX flow control configuration bits (see syslinux.txt)
522 -> bit 15 is set if the video console is disabled
524 If no serial port is configured, DX will be set to 0 and the
525 other registers are undefined.
528 AX=000Ch [2.00] Perform final cleanup
529 Input: AX 000Ch
530 DX derivative-specific flags (0000h = clean up all)
531 Output: None
533 This routine performs any "final cleanup" the boot loader
534 would normally perform before loading a kernel, such as
535 unloading the PXE stack in the case of PXELINUX. AFTER
536 INVOKING THIS CALL, NO OTHER API CALLS MAY BE INVOKED, NOR MAY
537 THE PROGRAM TERMINATE AND RETURN TO THE BOOT LOADER. This
538 call basically tells the boot loader "get out of the way, I'll
539 handle it from here."
541 For COM32 images, the boot loader will continue to provide
542 interrupt and BIOS call thunking services as long its memory
543 areas (0x0800-0xffff, 0x100000-0x100fff) are not overwritten.
544 MAKE SURE TO DISABLE INTERRUPTS, AND INSTALL NEW GDT AND IDTS
545 BEFORE OVERWRITING THESE MEMORY AREAS.
547 The permissible values for DX is an OR of these values:
549 SYSLINUX: 0000h Normal cleanup
551 PXELINUX: 0000h Normal cleanup
552 0003h Keep UNDI and PXE stacks loaded
554 ISOLINUX: 0000h Normal cleanup
556 EXTLINUX: 0000h Normal cleanup
558 All other values are undefined, and may have different
559 meanings in future versions of Syslinux.
562 AX=000Dh [2.08] Cleanup and replace bootstrap code
563 Input: AX 000Dh
564 DX derivative-specific flags (see previous function)
565 EDI bootstrap code (linear address, can be in high memory)
566 ECX bootstrap code length in bytes (must fit in low mem)
567 EBX(!) initial value of EDX after bootstrap
568 ESI initial value of ESI after bootstrap
569 DS initial value of DS after bootstrap
570 Output: Does not return
572 This routine performs final cleanup, then takes a piece of
573 code, copies it over the primary bootstrap at address 7C00h,
574 and jumps to it. This can be used to chainload boot sectors,
575 MBRs, bootstraps, etc.
577 Normal boot sectors expect DL to contain the drive number,
578 and, for hard drives (DL >= 80h) DS:SI to contain a pointer to
579 the 16-byte partition table entry. The memory between
580 600h-7FFh is available to put the partition table entry in.
582 For PXELINUX, if the PXE stack is not unloaded, all registers
583 (except DS, ESI and EDX) and the stack will be set up as they
584 were set up by the PXE ROM.
587 AX=000Eh [2.11] Get configuration file name
588 Input: AX 0000Eh
589 Output: ES:BX null-terminated file name string
591 Returns the name of the configuration file. Note that it is
592 possible that the configuration file doesn't actually exist.
595 AX=000Fh [3.00] Get IPAPPEND strings [PXELINUX]
596 Input: AX 000Fh
597 Output: CX number of strings (currently 2)
598 ES:BX pointer to an array of NEAR pointers in
599 the same segment, one for each of the above
600 strings
602 Returns the same strings that the "ipappend" option would have
603 added to the command line, one for each bit of the "ipappend"
604 flag value, so entry 0 is the "ip=" string and entry 1 is the
605 "BOOTIF=" string.
608 AX=0010h [3.00] Resolve hostname [PXELINUX]
609 Input: AX 0010h
610 ES:BX pointer to null-terminated hostname
611 Output: EAX IP address of hostname (zero if not found)
613 Queries the DNS server(s) for a specific hostname. If the
614 hostname does not contain a dot (.), the local domain name
615 is automatically appended.
617 This function only return CF=1 if the function is not
618 supported. If the function is supported, but the hostname did
619 not resolve, it returns with CF=0, EAX=0.
621 The IP address is returned in network byte order, i.e. if the
622 IP address is 1.2.3.4, EAX will contain 0x04030201. Note that
623 all uses of IP addresses in PXE are also in network byte order.
626 AX=0011h [3.05] Obsoleted in 3.80
629 AX=0012h [3.50] Cleanup, shuffle and boot
630 Input: AX 0012h
631 DX derivative-specific flags (see function 000Ch)
632 ES:DI shuffle descriptor list (must be in low memory)
633 CX number of shuffle descriptors
634 EBX(!) initial value of EDX after bootstrap
635 ESI initial value of ESI after bootstrap
636 DS initial value of DS after bootstrap
637 EBP CS:IP of routine to jump to
638 Output: Does not return
639 (if CX is too large the routine returns with CF=1)
641 This routine performs final cleanup, then performs a sequence
642 of copies, and jumps to a specified real mode entry point.
643 This is a more general version of function 000Dh, which can
644 also be used to load other types of programs.
646 The copies must not touch memory below address 7C00h.
648 ES:DI points to a list of CX descriptors each of the form:
650 Offset Size Meaning
651 0 dword destination address
652 4 dword source address
653 8 dword length in bytes
655 The copies are overlap-safe, like memmove().
657 Starting in version 3.50, if the source address is -1
658 (FFFFFFFFh) then the block specified by the destination
659 address and the length is set to all zero.
661 Starting in version 3.50, if the destination address is -1
662 (FFFFFFFFh) then the data block is loaded as a new set of
663 descriptors, and processing is continued (and unprocessed
664 descriptors are lost, this is thus typically only used as the
665 last descriptor in a block.) The block must still fit in the
666 internal descriptor buffer (see function 0011h), but can, of
667 course, itself chain another block.
670 Normal boot sectors expect DL to contain the drive number,
671 and, for hard drives (DL >= 80h) DS:SI to contain a pointer to
672 the 16-byte partition table entry. The memory between
673 600h-7FFh is available to put the partition table entry in.
675 For PXELINUX, if the PXE stack is not unloaded, all registers
676 (except DS, ESI and EDX) and the stack will be set up as they
677 were set up by the PXE ROM.
679 This interface was probably broken before version 3.50.
682 AX=0013h [3.08] Idle loop call
683 Input: AX 0013h
684 Output: None
686 Call this routine while sitting in an idle loop. It performs
687 any periodic activities required by the filesystem code. At
688 the moment, this is a no-op on all derivatives except
689 PXELINUX, where it executes PXE calls to answer ARP queries.
691 Starting with version 3.10, this API call harmlessly returns
692 failure (CF=1) if invoked on a platform which does not need
693 idle calls. Additionally, it's safe to call this API call on
694 previous Syslinux versions (2.00 or later); it will just
695 harmlessly fail. Thus, if this call returns failure (CF=1),
696 it means that there is no technical reason to call this
697 function again, although doing so is of course safe.
700 AX=0014h [3.10] Local boot [PXELINUX, ISOLINUX]
701 Input: AX 0014h
702 DX Local boot parameter
703 Output: Does not return
705 This function invokes the equivalent of the "localboot"
706 configuration file option. The parameter in DX is the same
707 parameter as would be entered after "localboot" in the
708 configuration file; this parameter is derivative-specific --
709 see syslinux.txt for the definition.
712 AX=0015h [3.10] Get feature flags
713 Input: AX 0015h
714 Output: ES:BX pointer to flags in memory
715 CX number of flag bytes
717 This function reports whether or not this Syslinux version and
718 derivative supports specific features. Keep in mind that
719 future versions might have more bits; remember to treat any
720 bits beyond the end of the array (as defined by the value in
721 CX) as zero.
723 Currently the following feature flag is defined:
725 Byte Bit Definition
726 ----------------------------------------------------
727 0 0 Local boot (AX=0014h) supported
728 1 Idle loop call (AX=0013h) is a no-op
730 All other flags are reserved.
733 AX=0016h [3.10] Run kernel image
734 Input: AX 0016h
735 DS:SI Filename of kernel image (zero-terminated string)
736 ES:BX Command line (zero-terminated string)
737 ECX IPAPPEND flags [PXELINUX]
738 EDX Type of file (since 3.50)
739 Output: Does not return if successful; returns with CF=1 if
740 the kernel image is not found.
742 This function is similiar to AX=0003h Run command, except that
743 the filename and command line are treated as if specified in a
744 KERNEL and APPEND statement of a LABEL statement, which means:
746 - The filename has to be exact; no variants are tried;
747 - No global APPEND statement is applied;
748 - ALLOWOPTIONS and IMPLICIT statements in the configuration
749 file do not apply. It is therefore important that the
750 COMBOOT module doesn't allow the end user to violate the
751 intent of the administrator.
753 Additionally, this function returns with a failure if the file
754 doesn't exist, instead of returning to the command line. (It
755 may still return to the command line if the image is somehow
756 corrupt, however.)
758 The file types are defined as follows:
760 Equivalent
761 EDX Config Extensions Type of file
762 0 KERNEL Determined by filename extension
763 1 LINUX none Linux kernel image
764 2 BOOT .bs .bin Bootstrap program
765 3 BSS .bss Boot sector with patch [SYSLINUX]
766 4 PXE .0 PXE Network Bootstrap Prog [PXELINUX]
767 5 FDIMAGE .img Floppy disk image [ISOLINUX]
768 6 COMBOOT .com .cbt 16-bit COMBOOT program
769 7 COM32 .c32 COM32 program
770 8 CONFIG Configuration file
773 AX=0017h [3.30] Report video mode change
774 Input: AX 0017h
775 BX Video mode flags
776 Bit 0: graphics mode
777 Bit 1: non-default mode
778 Bit 2: VESA mode
779 Bit 3: text functions not supported
780 CX For graphics modes, pixel columns
781 DX For graphics modes, pixel rows
782 Output: None
784 This function is used to report video mode changes to
785 Syslinux. It does NOT actually change the video mode, but
786 rather, allows Syslinux to take appropriate action in response
787 to a video mode change. Modes that cannot be exited either
788 with the conventional BIOS mode set command (INT 10h, AH=00h)
789 or the VESA VBE mode set command (INT 10h, AX=4F02h) should
790 not be used.
792 This function returns with a failure if BX contains any bits
793 which are undefined in the current version of Syslinux.
795 The following bits in BX are currently defined:
797 Bit 0: graphics mode
799 Indicates that the mode is a graphics mode, as opposed
800 to a text mode.
802 Bit 1: non-standard mode
804 A non-standard mode is any mode except text mode and
805 graphics mode 0012h (VGA 640x480, 16 color.)
807 Bit 2: VESA mode
809 This mode is a VESA mode, and has to be exited with
810 the VESA VBE API (INT 10h, AX=4F02h) as opposed to the
811 conventional BIOS API (INT 10h, AH=00h).
813 Bit 3: Text functions not supported
815 This indicates that the BIOS text output functions
816 (INT 10h, AH=02h, 03h, 06h, 09h, 0Eh, 11h) don't work.
817 If this bit is set, Syslinux will reset the mode
818 before printing any characters on the screen.
820 This is common for VESA modes.
823 AX=0018h [3.30] Query custom font
824 Input: AX 0018h
825 Output: AL Height of custom font in scan lines, or zero
826 ES:BX Pointer to custom font in memory
828 This call queries if a custom display font has been loaded via
829 the "font" configuration file command. If no custom font has
830 been loaded, AL contains zero.
833 AX=0019h [3.50] Read disk [SYSLINUX, ISOLINUX, EXTLINUX]
834 Input: AX 0019h
835 EDX Sector number
836 ESI Reserved - MUST BE ZERO
837 EDI Reserved - MUST BE ZERO
838 CX Sector count
839 ES:BX Buffer address
840 Output: None
842 Read disk blocks from the active filesystem (partition); for
843 disks, sector number zero is the boot sector. For ISOLINUX,
844 this call reads the CD-ROM.
846 For compatiblity with all systems, the buffer should
847 *neither* cross 64K boundaries, *nor* wrap around the segment.
849 This routine reports "boot failed" (and does not return) on
850 disk error.
852 Note: for ISOLINUX in hybrid mode, this call uses simulated
853 2048-byte CD-ROM sector numbers.
856 AX=001Ah [3.50] Obsoleted in 3.80
859 AX=001Bh [3.50] Obsoleted in 3.80
862 AX=001Ch [3.60] Get pointer to auxilliary data vector
863 Input: AX 001Ch
864 Output: ES:BX Auxilliary data vector
865 CX Size of the ADV (currently 500 bytes)
867 The auxillary data vector is a tagged data structure used
868 to carry a small amount of information (up to 500 bytes) from
869 one boot to another.
872 AX=001Dh [3.60] Write auxilliary data vector
873 Input: AX 001Dh
874 Output: None
876 Write the auxilliary data vector back to disk. Returns
877 failure for non-disk-based derivatives unless the "auxdata"
878 configuration command is used to specify a disk location
879 (not yet implemented.)
881 In a future version, PXELINUX may end up attempting to save
882 the ADV on the server via TFTP write.
885 AX=001Eh [3.74] Keyboard remapping table
886 Input: AX 001Eh
887 DX 0000h - all other values reserved
888 Output: AX format version (1)
889 CX length in bytes (256)
890 ES:BX pointer to keyboard table
892 This call queries the keyboard remapping table. For the current
893 version, the format code is always 1 and the length is always
894 256. This version can be updated simply by overwriting the version
895 in memory; this may not be true in the future.
898 AX=001Fh [3.74] Get current working directory
899 Input: AX 0001Fh
900 Output: ES:BX null-terminated directory name string
902 Returns the current working directory.
905 AX=0020h [3.74] Obsoleted in 4.00
906 AX=0021h [3.74] Obsoleted in 4.00
907 AX=0022h [3.74] Obsoleted in 4.00
909 These three functions provided opendir/readdir/closedir
910 functionality in the late 3.xx series. They have been
911 replaced by the protected-mode interface.
914 AX=0023h [3.80] Get shuffler parameters
915 Input: AX 0023h
916 Output: CX size of shuffler "safe area" in bytes
917 Other registers reserved for future use
919 This call gives the size of the required shuffler "safe area",
920 in bytes; for call 0024h. In the future, it may provide
921 additional parameters.
924 AX=0024h [3.80] Cleanup, shuffle and boot, raw version
925 Input: AX 0024h
926 DX derivative-specific flags (see function 000Ch)
927 EDI shuffle descriptor list safe area
928 ESI shuffle descriptor list source
929 ECX byte count of shuffle descriptor list
930 Output: Does not return
932 This routine performs final cleanup, then performs a sequence
933 of copies, and jumps to a specified real mode entry point.
934 This is a more general version of function 000Dh, which can
935 also be used to load other types of programs.
937 Unlike previous obsolete versions of this function, there are
938 no restrictions that copies must not touch memory below
939 address 7C00h. Either the shuffle descriptor list or the safe
940 area (or both) may be located in high memory.
942 ESI points to a list of descriptors each of the form:
944 Offset Size Meaning
945 0 dword destination address
946 4 dword source address (-1 = zero)
947 8 dword length in bytes (0 = end of list)
949 The copies are overlap-safe, like memmove().
951 Before actually executing the move list, the list is moved to
952 the address specified in EDI. The caller is responsibe to
953 ensure that the moved descriptor list plus a "safe area"
954 immediately afterwards (the size of which is specified by
955 function 0023h) is not disturbed by the copy sequence. It is,
956 however, safe to overwrite descriptors already consumed.
958 If the source address is -1 (FFFFFFFFh) then the block
959 specified by the destination address and the length is set to
960 all zero.
962 The list is terminated by an entry with length 0. For that
963 entry, the destination is used as an entry point, and the
964 source represents the type of entry point:
966 0 16-bit protected mode (dst is CS.base)
967 1 Flat 32-bit protected mode (dst is EIP)
969 This routine does not set up any GPR register state
970 whatsoever, including stack. It is the responsibility of the
971 caller to make sure the entry point provided sets up any
972 registers needed.
974 For mode 0 (16-bit real mode), EAX will contain CR0 with bit 0
975 masked out, suitable for loading into CR0 to immediately enter
976 real mode. Note: if real-mode entry is planned,
977 (CS.base & 0xfff0000f) should == 0 for compatibility with KVM,
978 and possibly other virtualization solutions.
980 In both mode 0 and mode 1, the data segments will be loaded
981 with read/write data segments, matching the respective code
982 segment. For mode 0, B=0 and the limits will be 64K, for mode
983 1, B=1 and the limits will be 4 GB.
986 ++++ 32-BIT ONLY API CALLS ++++
988 void *pm_cs->lmalloc(size_t bytes)
990 Allocate a buffer in low memory (below 1 MB).
993 void pm_cs->lfree(void *ptr)
995 Free a buffer allocated with pm_cs->lmalloc().
998 DIR *pm_cs->opendir(const char *pathname)
1000 Open a directory.
1003 struct dirent *pm_cs->readdir(DIR *dir)
1005 Read an entry from a directory. The entry is returned in a
1006 static buffer.
1009 int pm_cs->closedir(DIR *dir)
1011 Close a directory.