Re: HELP with linker script!!!

[Nick Clifton <nickc at redhat dot com>]

Hi Pieter,

> I read the the Red Hat manual "Using ld, the GNU Linker",

First of all it is not a Red Hat manual.  It is the binutils project's 
linker manual.   You might have been confused by the fact that the 
binutils project is hosted at the sources.redhat.com domain, but this is 
a resource provided by Red Hat to the Free Software community and it 
does not make the linker or its manual Red Hat property in any way.

> but I'm having 
> trouble. Essentially, I'd like to take specific symbols and assign them 
> to a memory region, rather than just take a section and assign it to a 
> memory region. 

A practical example of the problem that you are trying to solve would help.

The linker does not have the facility to assign individual symbols to a 
memory region.  Instead, as Grigory has already mentioned, the way to 
achieve what you want is to use a custom section to contain the symbols 
that you are interested in, and then have the linker script assign this 
custom section to a specific memory region.  His email shows you how to 
do this.

> Additionally, where do I define the start and end regions of my stack 
> and heap? I use .bss for uninitialized variables, .data for initialized 
> variables, but how do I reference the beginning and end of stack and the 
> beginning and end of heap?

That is up to you and will probably be dictated by the hardware you are 
using and the amount of available memory.  One common design is to have 
the heap start at the end of the allocated sections, usually after the 
.bss section, and grow upwards through memory.  Meanwhile the stack is 
placed to start at the end of the available memory and grow downwards. 
(This does assume that the ABI for the processor you are using has a 
downwards growing stack).

The location for the start of the heap and the start of the stack will 
normally be set up by your linker script and so you can associate 
symbols with these locations.  Finding the current end-of-heap and 
end-of-stack however is hardware specific.  Usually a hardware register 
will be used as a stack pointer and so contain the end-of-stack address. 
 The end of heap however is usually held in a private variable 
somewhere inside the operating system's memory allocation code and may 
not be accessible to application programs.

Cheers
  Nick