7.7 Reserving an empty region

You can reserve an empty block of memory with a scatter file, such as the area used for the stack. Use the EMPTY attribute for the execution region in the 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:
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 for placing the stack
    }
    HEAP +0 EMPTY 0x10000             ; region starts at the end of previous
                                      ; region. End of region calculated using
                                      ; positive length
    {
                                      ; Empty region for placing the 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.
Figure 7-5 Reserving a region for the stack
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In this example, the linker generates the symbols:
Image$$STACK$$ZI$$Base      = 0x7f0000
Image$$STACK$$ZI$$Limit     = 0x800000
Image$$STACK$$ZI$$Length    = 0x10000
Image$$HEAP$$ZI$$Base       = 0x800000
Image$$HEAP$$ZI$$Limit      = 0x810000
Image$$HEAP$$ZI$$Length     = 0x10000

Note

The EMPTY attribute applies only to an execution region. The linker generates a warning and ignores an EMPTY attribute used in a load region definition.
The linker checks that the address space used for the EMPTY region does not coincide with any other execution region.
Related concepts
8.4 Execution region descriptions
Related reference
6.3.2 Image$$ execution region symbols
8.4.3 Execution region attributes
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