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From: rosenber@ra.abo.fi (Robin Rosenberg INF)
Newsgroups: comp.sys.amiga.programmer
Subject: Re: Help! (AmigaDOS CreateProc/LoadSeg)
Message-ID: <ROSENBER.91Mar11193029@ra.abo.fi>
Date: 11 Mar 91 17:30:29 GMT
References: <63329@eerie.acsu.Buffalo.EDU> <19578@cbmvax.commodore.com>
	<06417.AA06417@babylon.rmt.sub.org>
Sender: rosenber@ra.abo.fi
Organization: Abo Akademi University, Finland
Lines: 48
In-reply-to: rbabel@babylon.rmt.sub.org's message of 6 Mar 91 11:58:01 GMT

In article <06417.AA06417@babylon.rmt.sub.org> rbabel@babylon.rmt.sub.org (Ralph Babel) writes:
>In article <19578@cbmvax.commodore.com>,
>ken@cbmvax.commodore.com (Ken Farinsky - CATS) writes:
>> LoadSeg() needs a BPTR to a seg list, which can be faked
>> like:
>>
>>         /* From Mike Sinz AmigaMail example */
>>         struct CodeHdr
>>                 {
>>                 ULONG SegSize;   /* sizeof(struct CodeHdr) */
>>                 ULONG NextSeg;   /* Must be NULL */
>>                 UWORD JumpInstr; /* set to 0x4EF9 (a jump instruction) */
>>                 APTR Function;   /* a pointer to the function */
>>                 }

>I'd call this self-modifying code.

>Ralph

I have a slightly different version, that does not contain
self-modifying code.  Instead of patching the jump instrction, I patch
data for the instruction. This code is of course not reentrant.

struct FakeSeg {
        LONG size;
        BPTR next;
        LONG move_inst;
        WORD jump_inst;
        APTR codeptr;
};

static struct FakeSeg __far FS = {
        0,0,
        0x207A0004,     /* MOVEA.L 4(PC),A0 */
        0x4ED0,         /* JMP (A0) */
        0               /* *DATA*, not code */
};

struct MsgPort *QuickCreateProc(UBYTE name,LONG pri,APTR func,LONG stacksize)
{
        /* Now I modify the faked segment, no not the code, only the data */
        FS.codeptr = func;
        return CreateProc(name,pri, (ULONG)&FS.next >> 2 ,stacksize);
}

Have fun

	Robin