Re: x86-64 medium memory model

["Leif Ekblad" <leif at rdos dot net>]

The small memory model will not do since I want to put data at other 
distinct addresses above 4G. I also want to place the heap at yet another 
address interval. This way it becomes easy to separate out code, data and 
heap references, and making sure that pointers are valid. The primary reason 
for not using below 2G or the last 2G, is because such numbers are formed 
naturally when doing 32-bit arithmetics, and thus could be executed by 
chance from corrupt data.

If I understand it correctly, the PIE option is very similar to the PIC 
option, and will not make it possible to use any address for both code and 
data.

Additionally, when I tried the small memory model with a start address of 
text above 4G, the linker complains about 32-bit fixups overflowing.

Leif Ekblad


----- Original Message ----- 
From: "H.J. Lu" <hjl.tools@gmail.com>
To: "Leif Ekblad" <leif@rdos.net>
Cc: "GCC Patches" <gcc-patches@gcc.gnu.org>; "GCC Mailing List" 
<gcc@gcc.gnu.org>
Sent: Wednesday, December 12, 2012 9:59 PM
Subject: Re: x86-64 medium memory model


> On Wed, Dec 12, 2012 at 12:56 PM, Leif Ekblad <leif@rdos.net> wrote:
> > I'm working on OS-adaptations for an OS that would use x86-64 
> > applications
> > that are located above 4G, but not in the upper area. Binutils provide a
> > function to be able to set the start of text to above 4G, but there are
> > problems with GCC when using this memory model.
>
> Have you tried PIE with small model?  You can place your
> binaries above 4G with better performance.
>
> --
> H.J.