en:docs:dos:api:int21:4b

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en:docs:dos:api:int21:4b [2021/05/02 04:50] – created prokusheven:docs:dos:api:int21:4b [2024/05/03 02:15] (current) – prokushev
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 ===== Notes ===== ===== Notes =====
  
- DOS 2.x destroys all registers, including SS:SP +DOS 2.x destroys all registers, including SS:SP 
- under ROM-based DOS, if no disk path characters (colons or slashes) + 
-   are included in the program name, the name is searched for in the +under ROM-based DOS, if no disk path characters (colons or slashes) are included in the program name, the name is searched for in the ROM module headers (see #01595) before searching on disk 
-   ROM module headers (see #01595) before searching on disk + 
- for functions 00h and 01h, the calling process must ensure that there +for functions 00h and 01h, the calling process must ensure that there is enough unallocated memory available; if necessary, by releasing memory with AH=49h or AH=4Ah 
-   is enough unallocated memory available; if necessary, by releasing + 
-   memory with AH=49h or AH=4Ah +for function 01h, the AX value to be passed to the child program is put on top of the child's stack 
- for function 01h, the AX value to be passed to the child program is put + 
-   on top of the child's stack +for function 03h, DOS assumes that the overlay is being loaded into memory allocated by the caller 
- for function 03h, DOS assumes that the overlay is being loaded into + 
-   memory allocated by the caller +function 01h was undocumented prior to the release of DOS 5.0 
- function 01h was undocumented prior to the release of DOS 5.0 + 
- some versions (such as DR DOS 6.0) check the parameters and parameter +some versions (such as DR DOS 6.0) check the parameters and parameter block and return an error if an invalid value (such as an offset of FFFFh) is found 
-   block and return an error if an invalid value (such as an offset of + 
-   FFFFh) is found +background programs under European MS-DOS 4.0 must use the new executable format 
- background programs under European MS-DOS 4.0 must use the new + 
-   executable format +this function ignores the filename extension, instead checking the first two bytes of the file to determine whether there is a valid .EXE header (see #01594); if not, the file is assumed to be in .COM format.  If present, the file may be in any of several formats which are extensions of the original .EXE format (see #01593) 
- this function ignores the filename extension, instead checking the + 
-   first two bytes of the file to determine whether there is a valid +.COM-format executables begin running with the following register  values: 
-   .EXE header (see #01594); if not, the file is assumed to be in .COM +
-   format.  If present, the file may be in any of several formats which +
-   are extensions of the original .EXE format (see #01593) +
- .COM-format executables begin running with the following register +
-   values:+
  AL = 00h if first FCB has valid drive letter, FFh if not  AL = 00h if first FCB has valid drive letter, FFh if not
  AH = 00h if second FCB has valid drive letter, FFh if not  AH = 00h if second FCB has valid drive letter, FFh if not
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  SP = offset of last word available in first 64K segment  SP = offset of last word available in first 64K segment
  (note: AX is always 0000h under DESQview)  (note: AX is always 0000h under DESQview)
- old-format executables begin running with the following register + 
-   values:+old-format executables begin running with the following register values: 
  AL = 00h if first FCB has valid drive letter, FFh if not  AL = 00h if first FCB has valid drive letter, FFh if not
  AH = 00h if second FCB has valid drive letter, FFh if not  AH = 00h if second FCB has valid drive letter, FFh if not
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  SS:SP as defined in .EXE header  SS:SP as defined in .EXE header
  (note: AX is always 0000h under DESQview)  (note: AX is always 0000h under DESQview)
- new executables begin running with the following register values+ 
 +new executables begin running with the following register values 
  AX = environment segment  AX = environment segment
  BX = offset of command tail in environment segment  BX = offset of command tail in environment segment
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  DS = automatic data segment  DS = automatic data segment
  SS:SP = initial stack  SS:SP = initial stack
-   the command tail corresponds to an old executable's PSP:0081h and + 
-   following, except that the 0Dh is turned into a NUL (00h); new +the command tail corresponds to an old executable's PSP:0081h and following, except that the 0Dh is turned into a NUL (00h); new format executables have no PSP 
-   format executables have no PSP + 
- under the FlashTek X-32 DOS extender, only function 00h is supported +under the FlashTek X-32 DOS extender, only function 00h is supported and the pointers are passed in DS:EDX and ES:EBX 
-   and the pointers are passed in DS:EDX and ES:EBX + 
- DR DOS 6 always loads .EXE-format programs with no fixups and +DR DOS 6 always loads .EXE-format programs with no fixups and .COM-format programs starting with 9Ch 55h (PUSHF/PUSH BP) above the 64K mark to avoid the EXEPACK bug, by extending the memory block containing the program's environment; this code is disabled if the name of the parent program as stored in the MCB is 'WIN'. 
-   .COM-format programs starting with 9Ch 55h (PUSHF/PUSH BP) above the + 
-   64K mark to avoid the EXEPACK bug, by extending the memory block +DR DOS 3.41 and 5.0 check for a valid filename before testing the subfunction number, so the otherwise invalid subfunction 02h will only return error code 01h if the given filename actually exists; otherwise, errors 02h, 03h, or 05h are returned 
-   containing the program's environment; this code is disabled if the + 
-   name of the parent program as stored in the MCB is 'WIN'. +BUGS: DOS 2.00 assumes that DS points at the current program's PSP 
- DR DOS 3.41 and 5.0 check for a valid filename before testing the + 
-   subfunction number, so the otherwise invalid subfunction 02h will +Load Overlay (subfunction 03h) loads up to 512 bytes too many if the file contains additional data after the actual overlay 
-   only return error code 01h if the given filename actually exists; + 
-   otherwise, errors 02h, 03h, or 05h are returned +Load but Do Not Execute (subfunction 01h) is reported to corrupt the top word of the caller's stack if the loaded module terminates with INT 21/AH=4Ch in some versions of MS-DOS, including v5.00. 
-  BUGS: DOS 2.00 assumes that DS points at the current program's PSP +
- Load Overlay (subfunction 03h) loads up to 512 bytes too many if the +
-   file contains additional data after the actual overlay +
- Load but Do Not Execute (subfunction 01h) is reported to corrupt the +
-   top word of the caller's stack if the loaded module terminates with +
-   INT 21/AH=4Ch in some versions of MS-DOS, including v5.00.+
 ===== See also ===== ===== See also =====
  
-  AX=4B05h,AH=4Ch,AH=4Dh,AH=64h/BX=0025h,AH=8Ah,INT 2E,INT 60/DI=0604h+AX=[[en:docs:dos:api:int21:4b:05|4B05h]],AH=[[en:docs:dos:api:int21:4c|4Ch]],AH=[[en:docs:dos:api:int21:4d|4Dh]],AH=[[en:docs:dos:api:int21:64|64h]]/BX=0025h,INT 2E,INT 60/DI=0604h
  
 ===== Note ===== ===== Note =====