Mail Archives: djgpp/1999/01/29/10:28:17
Hi Mohamed,
> ----------
> De: Mohamed El-dawy[SMTP:msdawy AT hotmail DOT com]
> Enviada: Sexta-feira, 29 de Janeiro de 1999 11:53
> Para: djgpp AT delorie DOT com
> Assunto: paradox!
>
> Hi all,
> How are ya all? hope u r all perfectly okay!
>
> Here are some questions!! :-)
>
> 1) what is _djgpp_conventional_base? there is a mention of it in the FAQ
> but i dunno what it is! is there any explanation of it in the help
> files? which file? i couldn't find any explanation for it anywhere!!
> perhaps because i dunno how to search well! :-(
>
I readed in somewhere in FAQ that there is a default selector that address
all and only first 1MB of memory.
> and here is a simple paradox...
>
> (please correct me if i am wrong in any point here! I am not really 100%
> sure of what i am writing!)
> the 386 has some models of operation. of which i am only interested in
> two, the segmented model, and the flat model. I have understood that the
> flat model is the same as the segmented but with all segments set to the
> same values (i.e. they all point to the same descriptor). they all begin
> at 0 and span 4gb, right?
> Now...
> a) is there any kind of protection when using the flat mode? how comes?
> all the memory is available and i can write to anywhere without causing
> an exception!
> b) I assume djgpp runs in flat model! right? this is copied from faq...
> >Programs compiled with DJGPP can access all the physical memory on your
> >machine and support virtual memory. All this memory presents a flat
> address
> >space with no segmentation (you can say goodbye to far and huge
> pointers
> >and to memory models), and is only limited by the amount of virtual
> memory
> >supported by the DPMI server in use.
>
I think that all the DPMI servers use segmentation and DJGPP too!
> great... now all the memory is available! why do i get a SIGSEGV fault
> when i executed a very simple CLS function?
> mov edi,0xa0000
> mov ecx,16000
> mov eax,0
> rep stosd
>
Try to read a little more the FAQ and you will see the answers for your
questions.
> I am puzzled!
>
> 3) where can i find info about pages, page table... etc... i have read
> intel reference, but i couldn't understand any thing!! :-(
>
Neither the Intel Engineers understand the Intel reference!
> looking forward to hearing from u soon... ;-)!
>
I know that I was not of a great utility as I'm a Newbie too, but, I hope
that I wrote to you be usefull.
> with lots of luv,
> Mohamed El Dawy
>
José Paulo
Rio de Janeiro - Brazil
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