X-Authentication-Warning: delorie.com: mail set sender to djgpp-bounces using -f
From: "Rod Pemberton" <do_not_have AT bitfoad DOT cmm>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: protecting program memory
Date: Fri, 23 Mar 2007 21:16:04 -0400
Organization: Aioe.org NNTP Server
Lines: 51
Message-ID: <eu1u50$9ck$1@aioe.org>
References: <OF8FAF1ED8 DOT 483B1086-ON872572A7 DOT 0078F978-872572A7 DOT 007C4A14 AT seagate DOT com>
NNTP-Posting-Host: IVw7K97ih4IohxRqyKkqFw.user.aioe.org
X-Complaints-To: abuse AT aioe DOT org
X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1441
X-Priority: 3
X-Newsreader: Microsoft Outlook Express 6.00.2800.1437
X-MSMail-Priority: Normal
To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp
Reply-To: djgpp AT delorie DOT com


<Gordon DOT Schumacher AT seagate DOT com> wrote in message
news:OF8FAF1ED8 DOT 483B1086-ON872572A7 DOT 0078F978-872572A7 DOT 007C4A14 AT seagate DOT com...
>
> tim DOT nicholson AT skyforcekent DOT com wrote on 23 Mar 2007 04:16:50
> -0700:
>
> # Is there an easy way to protect the memory used to store the
> # program op codes from a rogue memory write from within the
> # application? I have a large (100,000+ line) DJGPP
> # application which sometimes crashes with SIGILL - It would
> # seem the program is cannibalizing itself! In order
> # to find how this is happening, I would like to protect the
> # entire block of memory that contains the application code
> # so that an exception occurs at the point the corruption occurs
> # rather than the point that the corrupted code is executed.
> #
> # I guest I need to make the memory block read only, but I am
> # not sure how to do that.
>
> Not without DPMI 1.0, you can't.
>
> But here's an alternative: checksum the executable space.
>
> You can get a pointer to the beginning of code and its size
> by applying some mild abuse of GCC and the linker map:
>
>    extern char*               _text  asm(".text");
>    extern char*               _etext asm("etext");
>    static char*               __my_progstart   = NULL;
>    static size_t              __my_progsize    = 0;
>    __my_progstart = (char*) &_text;
>    __my_progsize = (&_etext - &_text) - sizeof(void*);
>
> There are any number of things that you can do now, armed
> with that data!  (Look into instrumentation with GCC...)
>

Nice.  Thanks.

More info for my Grub MB header into first 8k of .exe without a linker
script problem...  Alternately, I was currently thinking about just
destubbing the .exe's DPMI host and RM startup code, prepending an MB header
using the same (DJ COFF?) 32-bit entry point as the DPMI host.


Later, for a while anyway...,

Rod Pemberton