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Linker User Guide

Conventions and feedback Overview of the linker Linking models supported by armlink Image structure and generation Using linker optimizations Getting information about images Accessing and managing symbols with armlink Using scatter files About scatter-loading When to use scatter-loading Scatter-loading command-line option Images with a simple memory map Images with a complex memory map Linker-defined symbols that are not defined when s Specifying stack and heap using the scatter file What is a root region? Creating root execution regions Using the FIXED attribute to create root regions Placing functions and data at specific addresses Placing a named section explicitly using scatter-l Placing unassigned sections with the .ANY module s Examples of using placement algorithms for .ANY se Example of next_fit algorithm showing behavior of Examples of using sorting algorithms for .ANY sect Selecting veneer input sections in scatter-loading Using __attribute__((section("name"))) t Using __at sections to place sections at a specifi Restrictions on placing __at sections Automatic placement of __at sections Manual placement of __at sections Placing a key in flash memory using __at Placing a structure over a peripheral register usi Placement of sections with overlays About placing ARM C and C++ library code Example of placing code in a root region Example of placing ARM C library code Example of placing ARM C++ library code Example of placing ARM library helper functions Reserving an empty region About creating regions on page boundaries Overalignment of execution regions and input secti Using preprocessing commands in a scatter file Expression evaluation in scatter files Using expression evaluation in a scatter file to a Equivalent scatter-loading descriptions for simple Type 1 image, one load region and contiguous execu Type 2 image, one load region and non-contiguous e Type 3 image, two load regions and non-contiguous Scatter file to ELF mapping

Type 1 image, one load region and contiguous execution regions

Type 1 image, one load region and contiguous execution regions

An image of this type consists of a single load region in the load view and three execution regions in the execution view. The execution regions are placed contiguously in the memory map.

--ro_base address specifies the load and execution address of the region containing the RO output section. The following example shows the scatter-loading description equivalent to using --ro_base 0x040000:

Example 34. Single load region and contiguous execution regions

LR_1 0x040000     ; Define the load region name as LR_1, the region starts at 0x040000.
{
    ER_RO +0      ; First execution region is called ER_RO, region starts at end of previous region.
                  ; However, since there is no previous region, the address is 0x040000.
    {
        * (+RO)   ; All RO sections go into this region, they are placed consecutively.
    }
    ER_RW +0      ; Second execution region is called ER_RW, the region starts at the end of the 
                  ; previous region	. The address is 0x040000 + size of ER_RO region.
    {
        * (+RW)   ; All RW sections go into this region, they are placed consecutively.
    }
    ER_ZI +0      ; Last execution region is called ER_ZI, the region starts at the end of the 
                  ; previous region at 0x040000 + the size of the ER_RO regions + the size of 
                  ; the ER_RW regions.
    {
        * (+ZI)   ; All ZI sections are placed consecutively here.
    }
}

In this example:

  • This description creates an image with one load region called LR_1 that has a load address of 0x040000.

  • The image has three execution regions, named ER_RO, ER_RW, and ER_ZI, that contain the RO, RW, and ZI output sections respectively. RO, RW are root regions. ZI is created dynamically at runtime. The execution address of ER_RO is 0x040000. All three execution regions are placed contiguously in the memory map by using the +offset form of the base designator for the execution region description. This enables an execution region to be placed immediately following the end of the preceding execution region.

Use the --reloc option to make relocatable images. Used on its own, --reloc makes an image similar to simple type 1, but the single load region has the RELOC attribute.

Show/hideropi example variant

In this variant, the execution regions are placed contiguously in the memory map. However, --ropi marks the load and execution regions containing the RO output section as position-independent.

The following example shows the scatter-loading description equivalent to using --ro_base 0x010000 --ropi:

Example 35. Position-independent code

LR_1 0x010000 PI        ; The first load region is at 0x010000. 
{
    ER_RO +0            ; The PI attribute is inherited from parent.
                        ; The default execution address is 0x010000, but the code can be moved.
    {
        * (+RO)         ; All the RO sections go here.
    }
    ER_RW +0 ABSOLUTE   ; PI attribute is overridden by ABSOLUTE.
    {
        * (+RW)         ; The RW sections are placed next	. They cannot be moved.
    }
    ER_ZI +0            ; ER_ZI region placed after ER_RW region.
    {
        * (+ZI)         ; All the ZI sections are placed consecutively here.
    }
}

ER_RO, the RO execution region, inherits the PI attribute from the load region LR_1. The next execution region, ER_RW, is marked as ABSOLUTE and uses the +offset form of base designator. This prevents ER_RW from inheriting the PI attribute from ER_RO. Also, because the ER_ZI region has an offset of +0, it inherits the ABSOLUTE attribute from the ER_RW region.

Copyright © 2007-2008, 2011-2012 ARM. All rights reserved.ARM DUI 0377D
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