Re: extern variable

[Jim Wilson <wilson@codesourcery.com>]

On Mon, 2009-08-03 at 09:44 +0530, sumanth wrote:
>        How can i make sure my tool chain knows the difference between 
> global variable r0 and register r0.

The simple solution is to either add a prefix to variable names, or to
add a prefix to register names.  In ELF, the convention is to not add a
prefix to variables names, we add a prefix to register names instead if
we need one, e.g. %eax on i386, or $4 on mips.

You can of course choose to add a prefix to variable names.  It just
isn't the convention.  See for instance how the arm-elf port works when
you use the -fleading-underscore option.

A less simple solution is to have an assembler syntax that avoids
ambiguity between register names and variable names.  If for instance
you have a move instruction that can accept either a register or a
variable as source, then you have an ambiguity.  You could instead have
a load instruction for reading memory, and a move instruction for
reading registers, and then you don't have an ambiguity anymore.  You
can also do things with addressing modes and relocation operators to
reduce ambiguities.

Jim