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Aucbvax.6908 fa.info-vax utzoo!decvax!ucbvax!info-vax Sun Apr 25 09:08:54 1982 Reading your DCL global symbol table from a program >From EPS@MIT-AI Sun Apr 25 08:58:10 1982 DCL symbols are somewhat simpler creatures than VMS logical names. Their queue head is located at CTL+^X28 (%X7FFEA238). Each entry consists of the usual fore and back pointers, a word containing the size of the entry, a byte which is nonzero if the symbol table is full, a byte indicating the number of optional characters (i.e. if I type $ foob*ar:== this byte will contain a 2, if the symbol has no abbreviation point it will contain 0), followed by the symbol name and equivalence as counted (.ASCIC) strings just as we had before with logical names. Of course there's gotta be a catch, or one of you would no doubt have figured this out before. There's a catch. ("That's some catch that Catch-22.")

defines nine CHMS services you can request of your CLI via the callback address passed to your main program as 8(AP) (see the description of LIB in the Run Time Library Reference Manual), or by calling SYS. You will notice that there are codes for defining local and global symbols. You will also note the absence of any way to read (translate) them. (Why would anyone want to read a DCL symbol? Jon Leech <LEECH@MC> decided that his LOGIN.COM took too long to execute and wrote a LOGIN.EXE to speed things up. Such a program needs to be able to do what .COM files can.). BTW, you can't define a symbol with CLI callback that contains an abbreviation point. I know, send in a SIR. Anyway, you'll notice also CREALOG and DELELOG which hack logical names in supervisor mode. These implement things like TEC, which have to stick around across image activations.

Oh yeah. The catch is that (for some reason known only to DEC, of course) this stuff is in pages protected SW, i.e. not readable in user mode, so the same stunt I pulled in SHOWGROUP doesn't work. Of course I wouldn't let a little thing like access mode stop me. You can't see them with EXAMINE/ASCII from command level either; DEC has EXAMINE fixed to PROBE against user accessibility. Replace the 'PROBER #3,R3,(R7)' at ^X2A41 in DCL.EXE with 'PROBER #2,R3,(R7)' if you think this an unjust restriction. However, you don't have to hack your DCL to read stuff in supervisor mode. A neat little "feature" of the logical name callbacks is that they don't probe their arguments! Thus when the and get done they are probed against supervisor mode. Time to be devious. * * * .TITLE SUPERREAD ; ; Read memory in supervisor mode ; Eric P. Scott, Caltech, April 1982 ; ; unsigned superread(len, src, dst) ; unsigned short len; /* number of bytes to transfer */ ; char *src; /* copy from */ ; char *dst; /* copy to */ ; ; Returns: ; SS Service successfully completed. ; SS src cannot be read or dst cannot be written. ; SS Process has exceeded logical name limit. ; SS Attempt to transfer more than 63 characters. ; LIB Wrong number of arguments. ; CLI No CLI. ; ; Restrictions: ; Must run under a CLI ; Should not be called at AST level ; .PSECT SUPERREAD,NOWRT,PIC,SHR,LONG .ENTRY SUPERREAD,^M CMPW (AP),#3 ; Takes exactly three arguments BNEQ 15$ TSTW 4(AP) ; Zero byte transfer OK BEQL 20$ MOVQ 4(AP),-(SP) ; Request Super PUSHAB LOGNAM PUSHL #LOGLEN!<DSC@16>!<DSC@24> PUSHL #CLI!<CLI@8> PUSHAL (SP) CALLS #1,@#SYS BLBC R0,10$ MOVL 12(AP),16(SP) ; TRNLOG to dst buffer PUSHL #3 ; Search process table only CLRQ -(SP) PUSHAQ 12+12(SP) CLRL -(SP) PUSHAQ 4+20(SP) CALLS #6,@#SYS BLBC R0,10$ MOVL #CLI!<CLI@8>,(SP) PUSHAL (SP) ; Request Super CALLS #1,@#SYS 10$: RET 15$: MOVL #LIB,R0 RET 20$: MOVZWL #1,R0 RET .PSECT _SUPERREAD,NOWRT,NOEXE,SHR,LONG LOGNAM: .ASCII /SUPERREAD___VMS_IS_TWITLY/ LOGLEN=.-LOGNAM .END * * * The program to use this to read DCL symbols is left as an exercise (awww). I've already done it, don't send in the solution. Note that the equivalences can be longer than 63 characters so you'll have to call SUPERREAD repeatedly in some cases. Good luck! --Eric

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