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Execution region attributes

An execution region has attributes that allow you to control where parts of your image are loaded in the target memory at runtime.

The execution region attributes are:

ABSOLUTE
The content is placed at a fixed address that does not change after linking. A base designator specifies the execution address of the region.
ALIGN alignment

Increase the alignment constraint for the execution region from 4 to alignment. alignment must be a positive power of 2. If the execution region has a base_address, then the address must be alignment aligned. If the execution region has a +offset, then the linker aligns the calculated base address of the region to an alignment boundary.

Note

ALIGN on an execution region causes both the load address and execution address to be aligned. This alignment can result in padding being added to the ELF file. To align only the execution address, use the AlignExpr expression on the base address.
ALIGNALL value

Increases the alignment of sections within the execution region.

The value must be a positive power of 2 and must be greater than or equal to 4.

ANY_SIZE max_size

Specifies the maximum size within the execution region that armlink can fill with unassigned sections. You can use a simple expression to specify the max_size. That is, you cannot use functions such as ImageLimit().

Note

Specifying ANY_SIZE overrides any effects that --any_contingency has on the region.

Be aware of the following restrictions when using this keyword:

  • max_size must be less than or equal to the region size.
  • You can use ANY_SIZE on a region without a .ANY selector but armlink ignores it.
AUTO_OVERLAY

Use to indicate regions of memory where armlink assigns the overlay sections for loading into at runtime. Overlay sections are those named .ARM.overlayN in the input object.

The execution region must not have any section selectors.

The addresses that you give for the execution regions are the addresses that armlink expects the overlaid code to be loaded at when running. The load region containing the execution regions is where armlink places the overlay contents.

By default, the overlay manager loads overlays by copying them into RAM from some other memory that is not suitable for direct execution. For example, very slow Flash or memory from which instruction fetches are not enabled. You can keep your unloaded overlays in peripheral storage that is not mapped into the address space of the processor. To keep such overlays in peripheral storage, you must extract the data manually from the linked image.

armlink allocates every overlay to one of the AUTO_OVERLAY execution regions, and has to be loaded into only that region to run correctly.

You must use the --overlay_veneers command-line option when linking with a scatter file containing the AUTO_OVERLAY attribute.

Note

With the AUTO_OVERLAY attribute, armlink decides how your code sections get allocated to overlay regions. With the OVERLAY attribute, you must manually arrange the allocation of the code sections.
EMPTY [–]length

Reserves an empty block of memory of a given size in the execution region, typically used by a heap or stack. No section can be placed in a region with the EMPTY attribute.

length represents a stack that grows down in memory. If the length is given as a negative value, the base_address is taken to be the end address of the region.

FILL value

Creates a linker generated region containing a value. If you specify FILL, you must give a value, for example: FILL 0xFFFFFFFF. The FILL attribute replaces the following combination: EMPTY ZEROPAD PADVALUE.

In certain situations, such as a simulation, filling a region with a value is preferable to spending a long time in a zeroing loop.

FIXED

Fixed address. The linker attempts to make the execution address equal the load address. If it succeeds, then the region is a root region. If it does not succeed, then the linker produces an error.

Note

The linker inserts padding with this attribute.
NOCOMPRESS
RW data compression is enabled by default. The NOCOMPRESS keyword enables you to specify that RW data in an execution region must not be compressed in the final image.
OVERLAY

Use for sections with overlaying address ranges. If consecutive execution regions have the same +offset, then they are given the same base address.

The content is placed at a fixed address that does not change after linking. The content might overlap with other regions designated as OVERLAY regions.

PADVALUE value

Defines the value to use for padding. If you specify PADVALUE, you must give a value, for example:

EXEC 0x10000 PADVALUE 0xFFFFFFFF EMPTY ZEROPAD 0x2000

This example creates a region of size 0x2000 full of 0xFFFFFFFF.

PADVALUE must be a word in size. PADVALUE attributes on load regions are ignored.

PI

This region contains only position independent sections. The content does not depend on any fixed address and might be moved after linking without any extra processing.

Note

PI is not supported for AArch64 state.

Note

This attribute is not supported if an image contains execute-only sections.
SORTTYPE algorithm

Specifies the sorting algorithm for the execution region, for example:

ER1 +0 SORTTYPE CallTree

Note

This attribute overrides any sorting algorithm that you specify with the --sort command-line option.
UNINIT

Use to create execution regions containing uninitialized data or memory-mapped I/O. Only ZI output sections are affected. For example, in the following ER_RW region only the ZI part is uninitialized:

LR 0x8000
{
    ER_RO +0
    {
        *(+RO)
    }
    ER_RW 0x10000 UNINIT
    {
        *(+RW,+ZI)
    }
}

Note

ARM® Compiler does not support systems with ECC or parity protection where the memory is not initialized.
ZEROPAD

Zero-initialized sections are written in the ELF file as a block of zeros and, therefore, do not have to be zero-filled at runtime.

This attribute sets the load length of a ZI output section to Image$$region_name$$ZI$$Length.

Only root execution regions can be zero-initialized using the ZEROPAD attribute. Using the ZEROPAD attribute with a non-root execution region generates a warning and the attribute is ignored.

In certain situations, such as a simulation, filling a region with a value is preferable to spending a long time in a zeroing loop.

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