define block directive

In this section:

Syntax

define [ movable ] block name 
  [ with param, param... ]
{
  extended-selectors
}
[ except
 {
   section-selectors
  } ];

where param can be one of:

size = expr
minimum size = expr
maximum size = expr
expanding size
alignment = {expr|input}
end alignment = expr
fixed order
alphabetical order
static base [basename]

and where the rest of the directive selects sections to include in the block, see Section selection.

Parameters

`name`	The name of the block to be defined.
`size`	Customizes the size of the block. By default, the size of a block is the sum of its parts dependent of its contents.
`minimum size`	Specifies a lower limit for the size of the block. The block is at least this large, even if its contents would otherwise not require it.
`maximum size`	Specifies an upper limit for the size of the block. An error is generated if the sections in the block do not fit.
`expanding size`	The block will expand to use all available space in the memory range where it is placed.
`alignment`	`expr` specifies a minimum alignment for the block's start address. Content in the block will always be placed so that its alignment requirement (as generated by the compiler/assembler, or the alignment of the contained block) is satisfied. Note that the content's own alignment cannot be lowered by placing the content in a block with a lower alignment. `input` sets the minimum alignment of the block's start address to the alignment of the highest alignment of any content in the block. Content in the block will be placed on an address that is aligned for that content's alignment requirements.
`end alignment`	Specifies a minimum alignment for the end of the block. Normally, the end address of a block is determined by its start address and its size (which can depend on its contents), but if this parameter is used, the end address is increased to comply with the specified alignment if needed.
`fixed order`	Places sections in the specified order. Each `extended-selector` is added in a separate nested block, and these blocks are kept in the specified order. Note that it is not possible to combine defining blocks `with fixed order` with initializing entire blocks `by copy`.
`alphabetical order`	Places sections in alphabetical order by section name. Only `section-selector` patterns are allowed in `alphabetical order` blocks, for example, no nested blocks. All sections in a particular `alphabetical order` block must use the same kind of initialization (read-only, zero-init, copy-init, or no-init, and otherwise equivalent). You cannot use `__section_begin`, etc., on individual sections contained in an `alphabetical order` block.
`static base` [`basename`]	32-bit mode only:Specifies that the static base with the name `basename` will be placed at the start of the block or in the middle of the block, as appropriate for the particular static base. The startup code must ensure that the register that holds the static base is initialized to the correct value. If there is only one static base, the name can be omitted. When linking for `‑‑rwpi`, the `basename` for writable data must be `SB`, and when linking for `‑‑ropi_cb`, the `basename` for read-only data must be `CB`.

Description

The define block directive defines a contiguous area of memory that contains a possibly empty set of sections or other blocks. Blocks with no content are useful for allocating space for stacks or heaps. Blocks with content are usually used to group together sections that must to be consecutive.

You can access the start, end, and size of a block from an application by using the __section_begin, __section_end, or __section_size operators. If there is no block with the specified name, but there are sections with that name, a block will be created by the linker, containing all such sections.

movable blocks are for use with read-only and read-write position independence. Making blocks movable enables the linker to validate the application’s use of addresses. Movable blocks are located in exactly the same way as other blocks, but the linker will check that the appropriate relocations are used when referring to symbols in movable blocks.

Blocks with expanding size are most often used for heaps or stacks.

Note

You cannot place a block with expanding size inside another block with expanding size, inside a block with a maximum size, or inside an overlay.

Example

/* Create a block with a minimum size for the heap that will use
   all remaining space in its memory range */
define block HEAP with minimum size = 4K, expanding size, alignment = 8 { };

IAR Embedded Workbench for Arm 9.70.x

define block directive

Syntax

Parameters

Description

Example

See also

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