From: Endlisnis <s257m AT unb DOT ca>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Generating Machine Code on the fly
Date: Sun, 28 Feb 1999 13:29:41 -0400
Organization: BrunNet
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Message-ID: <36D97D05.C4440EED@unb.ca>
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To: djgpp AT delorie DOT com
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Reply-To: djgpp AT delorie DOT com

Andrew Davidson wrote:

> Can anyone provide me with the inline assembler code to call the code in a
> given address in memory. It should go something like this I think:
>
> char *codehere;     /*void*, char* or what*/
> codehere=(char *)malloc(100);    /* 100 bytes of code memory */
> codehere[0]=0xc3;    /*just perform a ret operation for now*/
> asm(
>     "call %codehere",    /* don't know if this is right */
>     : /*no ouputs*/
>     : <what inputs?> (codehere)
>     : "%eax", "%ebx", "%ecx","%edx",
>       "%esi","%edi" /*anything else?*/
>     );
>
> This seems very,very wrong. I know absolutely nothing about using the gcc
> asm function so if you could explain this clearly in words of less than two
> sylables that would help ;)

    You can't access a local variable through "%codehere".  You will have to
put it as one of your inputs.  And you don't destroy the value in any
registers, so you don't need to list them.  [in this example].  I haven't done
this in a while so, there may be something wrong, but this is what I would do:

char *codehere;     /*void*, char* or what*/
codehere=(char *)malloc(100);    /* 100 bytes of code memory */
codehere[0]=0xc3;    /*just perform a ret operation for now*/
asm(
    "call %%ebx"    /* no comma after this */
    : /*no ouputs*/
    : b (codehere)   );


--
     (\/) Endlisnis (\/)
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