ARM Compiler User Guide : 5.11.2 Example of reserving an empty block of memory

5.11.2 Example of reserving an empty block of memory

This example shows how to reserve and empty block of memory for stack and heap using a scatter-loading description. It also shows the related symbols that the linker generates.

In the following example, the execution region definition STACK 0x800000 EMPTY –0x10000 defines a region that is called STACK. The region 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 5-3 Reserving a region for the stack

In this example, the linker generates the following 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 that is 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.

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