{{page>en:templates:dosint}} ====== Int 21H, AH=26H ====== ===== Version ===== 1 and higher ===== Brief ===== CREATE NEW PROGRAM SEGMENT PREFIX ===== Family API ===== ===== Input ===== AH = 26h DX = segment at which to create PSP (see #01378) ===== Return ===== Return: AL destroyed ===== Notes ===== new PSP is updated with memory size information; INTs 22h, 23h, 24h taken from interrupt vector table; the parent PSP field is set to 0 (DOS 2+) DOS assumes that the caller's CS is the segment of the PSP to copy BUG: DR DOS 6.0 original releases 05/1991 & 08/1991 had a problem where the segment from which the PSP was copied was incorrect so that the PSP was not filled correctly and did not contain the command tail. The DR DOS 6.0 BDOS patch "PAT312" English (1992/01/07, XDIR /C: A0C6h) and later "full" rebuilds fix this problem (see INT 21/AX=4452h). Format of Program Segment Prefix (PSP): ^ Offset ^ Size ^ Description ^ | 00h | 2 BYTEs | INT 20 instruction for CP/M CALL 0 program termination the CDh 20h here is often used as a signature for a valid PSP | | 02h | WORD | segment of first byte beyond memory allocated to program | | 04h | BYTE | (DOS) unused filler, (OS/2) count of fake DOS version returns | | 05h | BYTE | CP/M CALL 5 service request (FAR CALL to absolute 000C0h) BUG: (DOS 2+ DEBUG) PSPs created by DEBUG point at 000BEh | | 06h | WORD | CP/M compatibility--size of first segment for .COM files | | 08h | 2 BYTEs | remainder of FAR JMP at 05h | | 0Ah | DWORD | stored INT 22 termination address | | 0Eh | DWORD | stored INT 23 control-Break handler address | | 12h | DWORD | DOS 1.1+ stored INT 24 critical error handler address | | 16h | WORD | segment of parent PSP | | 18h | 20 BYTEs | DOS 2+ Job File Table, one byte per file handle, FFh = closed | | 2Ch | WORD | DOS 2+ segment of environment for process (see #01379) | | 2Eh | DWORD | DOS 2+ process's SS:SP on entry to last INT 21 call | | 32h | WORD | DOS 3+ number of entries in JFT (default 20) | | 34h | DWORD | DOS 3+ pointer to JFT (default PSP:0018h) | | 38h | DWORD | DOS 3+ pointer to previous PSP (default FFFFFFFFh in 3.x) used by SHARE in DOS 3.3 | | 3Ch | BYTE | DOS 4+ (DBCS) interim console flag (see AX=6301h) Novell DOS 7 DBCS interim flag as set with AX=6301h (possibly also used by Far East MS-DOS 3.2-3.3) | | 3Dh | BYTE | (APPEND) TrueName flag (see INT 2F/AX=B711h) | | 3Eh | BYTE | (Novell NetWare) flag: next byte initialized if CEh (OS/2) capabilities flag | | 3Fh | BYTE | (Novell NetWare) Novell task number if previous byte is CEh | | 40h | 2 BYTEs | DOS 5+ version to return on INT 21/AH=30h | | 42h | WORD | (MSWindows3) selector of next PSP (PDB) in linked list Windows keeps a linked list of Windows programs only | | 44h | WORD | (MSWindows3) "PDB_Partition" | | 46h | WORD | (MSWindows3) "PDB_NextPDB" | | 48h | BYTE | (MSWindows3) bit 0 set if non-Windows application (WINOLDAP) | | 49h | BYTE | unused by DOS versions <= 6.00 | | 4Ch | WORD | (MSWindows3) "PDB_EntryStack" | | 4Eh | 2 BYTEs | unused by DOS versions <= 6.00 | | 50h | 3 BYTEs | DOS 2+ service request (INT 21/RETF instructions) | | 53h | 2 BYTEs | unused in DOS versions <= 6.00 | | 55h | 7 BYTEs | unused in DOS versions <= 6.00; can be used to make first FCB into an extended FCB | | 5Ch | 16 BYTEs | first default FCB, filled in from first commandline argument overwrites second FCB if opened | | 6Ch | 16 BYTEs | second default FCB, filled in from second commandline argument overwrites beginning of commandline if opened | | 7Ch | 4 BYTEs | unused | | 80h | 128 BYTEs | commandline / default DTA. command tail is BYTE for length of tail, N BYTEs for the tail, followed by a BYTE containing 0Dh | Notes: in DOS v3+, the limit on simultaneously open files may be increased by allocating memory for a new open file table, filling it with FFh, copying the first 20 bytes from the default table, and adjusting the pointer and count at 34h and 32h. However, DOS will only copy the first 20 file handles into a child PSP (including the one created on EXEC). in an OS/2 DOS box, values of D0h-FEh in the open file table indicate device drivers network redirectors based on the original MS-Net implementation use values of 80h-FEh in the open file table to indicate remote files; Novell NetWare also uses values from FEh down to 80h or one more than FILES= (whichever is greater) to indicate remote files (except on OS/2, where is uses CFh down to 80h) MS-DOS 5.00 incorrectly fills the FCB fields when loading a program high; the first FCB is empty and the second contains the first parameter some DOS extenders place protected-mode values in various PSP fields such as the "parent" field, which can confuse PSP walkers. Always check either for the CDh 20h signature or that the suspected PSP is at the beginning of a memory block which owns itself (the preceding paragraph should be a valid MCB with "owner" the same as the suspected PSP). Novell NetWare updates the fields at offsets 3Eh and 3Fh without checking that a legal PSP segment is current; see AH=50h for further discussion for 4DOS and Windows95, the command tail may be more than 126 characters; in that case, the length byte will be set to 7Fh (with an 0Dh in the 127th position at offset FFh), and the first 126 characters will be stored in the PSP, with the entire command line in the environment variable CMDLINE; under at least some versions of 4DOS, the byte at offset FFh is *not* set to 0Dh, so there is no terminating carriage return in the PSP's command tail. BUG: When shelling out from the Borland Pascal 7.00 IDE, overly-long command lines will not be delimited by a 0Dh character, and the length byte is set to 80h! A workaround is to always patch in a 0Dh at the last position of the command line buffer before scanning the command line. Format of environment block: ^ Offset ^ Size ^ Description ^ | 00h | N BYTEs | first environment variable, ASCIZ string of form "var=value" | | ::: | N BYTEs | second environment variable, ASCIZ string | | ::: | ... | | ::: | N BYTEs | last environment variable, ASCIZ string of form "var=value" | | ::: | BYTE | 00h | | ---DOS 3.0+ --- ||| | ... | WORD | number of strings following environment (normally 1) | | ::: | N BYTEs | ASCIZ full pathname of program owning this environment other strings may follow | ===== See also ===== AH=[[en:docs:dos:api:int21:4b|4Bh]],AH=[[en:docs:dos:api:int21:50|50h]],AH=[[en:docs:dos:api:int21:51|51h]],AH=[[en:docs:dos:api:int21:55|55h]],AH=[[en:docs:dos:api:int21:62|62h]],AH=[[en:docs:dos:api:int21:67|67h]] ===== Note ===== Text based on [[http://www.cs.cmu.edu/~ralf/files.html|Ralf Brown Interrupt List Release 61]] {{page>en:templates:int}} {{page>en:templates:fapi}}