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Linker User Guide

Preface Overview of the Linker Linking Models Supported by armlink Image Structure and Generation Linker Optimization Features Getting Image Details Accessing and Managing Symbols with armlink Scatter-loading Features The scatter-loading mechanism Overview of scatter-loading When to use scatter-loading Linker-defined symbols that are not defined when s Specifying stack and heap using the scatter file Scatter-loading command-line options Scatter-loading images with a simple memory map Scatter-loading images with a complex memory map Scatter file with link to bit-band objects Root execution regions Root execution region and the initial entry point Root execution regions and the ABSOLUTE attribute Root execution regions and the FIXED attribute Methods of placing functions and data at specific Placement of code and data with __attribute__((sec Placement of __at sections at a specific address Restrictions on placing __at sections Automatic placement of __at sections Manual placement of __at sections Placement of a key in flash memory with an __at se Mapping a structure over a peripheral register wit Example of how to explicitly place a named section Placement of unassigned sections with the .ANY mod Placement rules when using multiple .ANY selectors Command-line options for controlling the placement Prioritization of .ANY sections Specify the maximum region size permitted for plac Examples of using placement algorithms for .ANY se Example of next_fit algorithm showing behavior of Examples of using sorting algorithms for .ANY sect Behavior when .ANY sections overflow because of li Placement of veneer input sections in a scatter fi Placement of sections with overlays Reserving an empty region Placement of ARM C and C++ library code Specifying ARM standard C and C++ libraries in a s 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 Creation of regions on page boundaries Overalignment of execution regions and input secti Preprocessing of a scatter file Example of using expression evaluation in a scatte Equivalent scatter-loading descriptions for simple Command-line options for creating simple images Type 1 image, one load region and contiguous execu Type 2 image, one load region and non-contiguous e Type 3 image, multiple load regions and non-contig How the linker resolves multiple matches when proc How the linker resolves path names when processing Scatter file to ELF mapping Scatter File Syntax Linker Command-line Options Linker Steering File Command Reference Via File Syntax

Type 3 image, multiple load regions and non-contiguous execution regions

7.13.4 Type 3 image, multiple load regions and non-contiguous execution regions

A Type 3 image consists of multiple load regions in load view and multiple execution regions in execution view. They are similar to images of Type 2 except that the single load region in Type 2 is now split into multiple load regions.

You can relocate and split load regions using the following linker options:
--reloc
The combination --reloc --split makes an image similar to simple Type 3, but the two load regions now have the RELOC attribute.
--ro_base=address1
Specifies the load and execution address of the region containing the RO output section.
--rw_base=address2
Specifies the load and execution address for the region containing the RW output section.
--xo_base=address3
Specifies the load and execution address for the region containing the execute-only (XO) output section, if present.
--split
Splits the default single load region that contains the RO and RW output sections into two load regions. One load region contains the RO output section and one contains the RW output section.

Note

For images containing XO sections, and if --xo_base is not used, an XO execution region is placed at the address specified by --ro_base. The RO execution region is placed immediately after the XO region.

Example for multiple load regions

The following example shows the scatter-loading description equivalent to using --ro_base=0x010000 --rw_base=0x040000 --split:
LR_1 0x010000     ; The first load region is at 0x010000.
{    
    ER_RO +0      ; The address is 0x010000.
    {
        * (+RO)
    }
}
LR_2 0x040000     ; The second load region is at 0x040000.
{
    ER_RW +0      ; The address is 0x040000.
    {
        * (+RW)   ; All RW sections are placed consecutively into this region.
    }
    ER_ZI +0      ; The address is 0x040000 + size of ER_RW region.
    {
        * (+ZI)   ; All ZI sections are placed consecutively into this region.
    }
}
In this example:
  • This description creates an image with two load regions, named LR_1 and LR_2, that have load addresses 0x010000 and 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. The execution address of ER_RO is 0x010000.
  • The ER_RW execution region is not contiguous with ER_RO, because its execution address is 0x040000.
  • The ER_ZI execution region is placed immediately after ER_RW.

Example for multiple load regions with an XO region

The following example shows the scatter-loading description equivalent to using --ro_base=0x010000 --rw_base=0x040000 --split when an object file has XO sections:
LR_1 0x010000     ; The first load region is at 0x010000.
{    
    ER_XO +0      ; The address is 0x010000.
    {
        * (+XO)
    }
    ER_RO +0      ; The address is 0x010000 + size of ER_XO region.
    {
        * (+RO)
    }
}
LR_2 0x040000     ; The second load region is at 0x040000.
{
    ER_RW +0      ; The address is 0x040000.
    {
        * (+RW)   ; All RW sections are placed consecutively into this region.
    }
    ER_ZI +0      ; The address is 0x040000 + size of ER_RW region.
    {
        * (+ZI)   ; All ZI sections are placed consecutively into this region.
    }
}
In this example:
  • This description creates an image with two load regions, named LR_1 and LR_2, that have load addresses 0x010000 and 0x040000.
  • The image has four execution regions, named ER_XO, ER_RO, ER_RW and ER_ZI, that contain the XO, RO, RW, and ZI output sections respectively. The execution address of ER_XO is placed at the address specified by --ro_base, 0x010000. ER_RO is placed immediately after ER_XO.
  • The ER_RW execution region is not contiguous with ER_RO, because its execution address is 0x040000.
  • The ER_ZI execution region is placed immediately after ER_RW.

Note

If you also specify --xo_base, then the ER_XO execution region is placed in a load region separate from the ER_RO execution region, at the specified address.

Relocatable load regions example variant

This Type 3 image also consists of two load regions in load view and three execution regions in execution view. However, --reloc specifies that the two load regions now have the RELOC attribute.
The following example shows the scatter-loading description equivalent to using --ro_base 0x010000 --rw_base 0x040000 --reloc --split:
LR_1 0x010000 RELOC
{
     ER_RO + 0
     {
         * (+RO)
     }
} 
LR2 0x040000 RELOC
{
     ER_RW + 0
     {
         * (+RW)
     }
     ER_ZI +0
     { 
         * (+ZI)
     }
}
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