ARM Compiler toolchain Using the Linker - ARM Information Center

8.31 Reserving an empty region
Using scatter files
You can use the EMPTY attribute in an execution region scatter-loading description to reserve an
empty block of memory for the stack.
The block of memory does not form part of the load region, but is assigned for use at execution
time. Because it is created as a dummy ZI region, the linker uses the following symbols to access
it:
• Image$$region_name$$ZI$$Base
• Image$$region_name$$ZI$$Limit
• Image$$region_name$$ZI$$Length.
If the length is given as a negative value, the address is taken to be the end address of the region.
This must be an absolute address and not a relative one.
In the following example, the execution region definition STACK 0x800000 EMPTY –0x10000
defines a region called STACK that starts at address 0x7F0000 and ends at address 0x800000:
Example 8-20 Reserving a region for the stack
LR_1 0x80000 ; load region starts at 0x80000
{
STACK 0x800000 EMPTY -0x10000 ; region ends at 0x800000 because of the
; negative length. The start of the region
; is calculated using the length.
{
; Empty region used to place stack
}
HEAP +0 EMPTY 0x10000 ; region starts at the end of previous
; region. End of region calculated using
; positive length
{
; Empty region used to place heap
}
... ; rest of scatter-loading description...
}
Note
The dummy ZI region that is created for an EMPTY execution region is not initialized to zero at
runtime.
If the address is in relative (+offset) form and the length is negative, the linker generates an
error.
The following figure shows a diagrammatic representation for this example.
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