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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 1 image, one load region and contiguous execution regions

7.13.2 Type 1 image, one load region and contiguous execution regions

A Type 1 image consists of a single load region in the load view and up to four execution regions in the execution view. The execution regions are placed contiguously in the memory map.

By default, the ER_RO, ER_RW, and ER_ZI execution regions are present. If an image contains any execute-only (XO) sections, then an ER_XO execution region is also present.
--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:
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. Because 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 and 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.

ROPI 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:
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.

Note

If an image contains execute-only sections, ROPI is not supported. If you use --ropi to link such an image, armlink gives an error.
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