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Question on LD Linker providing low 2 bytes of address as a constant
- From: "Miller, Doreen" <domiller at tycoint dot com>
- To: <binutils at sourceware dot org>
- Date: Wed, 17 Oct 2007 11:23:11 -0400
- Subject: Question on LD Linker providing low 2 bytes of address as a constant
I am using GCC and LD to build for a ColdFire processer. My application
is a port of existing C and assembly code for an Intel processor. So, I
will start off by saying I am probably trying to do things that are not
typical or in the norm. And often I want to do things to minimize the
overal project risk.
In this case, there are things I am specifically storing in low memory
(address can fit in 2 bytes). These things are stored places and used
all as 2 byte addresses. They are then cast to real pointers when they
need to be dereferenced.
My problem is this. I have some constant tables (stored in flash) that
need to contain the 2 byte address of another table. If I end up
needing to change these to 4 bytes being stored in the table, this has a
large impact on my project. So, before going to that, I want to make
sure I have explored every option possible to get the linker to store
the low 2 bytes of an address in my constant table. My constant table
is a table of structures that contains among other things a 2 byte
address of another table (which is stored in low memory). I will refer
to this item in the structure as HdlrTbl and the table that contains the
2 byte pointer as StructTbl just for ease of discussion. So, StructTbl
is an array of structures containing HdlrTbl. HdlrTbl is defined as 2
If I put the address of the table I wanted stored in HdlrTbl in my
pre-initializer, the compiler reports "error: initializer element is not
constant". If I change HdlrTbl from 2 bytes to 4 bytes and leave the
pre-initilizer the way it was, it compiles fine. So it looks like I
need a way to tell the compiler and linker that I only want the lowest 2
bytes of the address (which is identical to the address since the 2 high
bytes are 0).
Any help you could give me would be greatly appreciated.
Tyco Fire & Security - SimplexGrinnell
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Westminster, MA 01441