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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

Examples of using placement algorithms for .ANY sections

7.4.5 Examples of using placement algorithms for .ANY sections

These examples show the operation of the placement algorithms for RO-CODE sections in sections.o.

The input section properties and ordering are shown in the following table:

Table 7-2 Input section properties for placement of .ANY sections

Name Size
sec1 0x4
sec2 0x4
sec3 0x4
sec4 0x4
sec5 0x4
sec6 0x4
The scatter file used for the examples is:
LR 0x100
{
  ER_1 0x100 0x10
  {
     .ANY
  }
  ER_2 0x200 0x10
  {
     .ANY
  }
}

Note

These examples have --any_contingency disabled.

Example for first_fit, next_fit, and best_fit

This example shows the situation where several sections of equal size are assigned to two regions with one selector. The selectors are equally specific, equivalent to .ANY(+R0) and have no priority.
    Execution Region ER_1 (Base: 0x00000100, Size: 0x00000010, Max: 0x00000010, ABSOLUTE)

    Base Addr    Size         Type   Attr      Idx    E Section Name        Object

    0x00000100   0x00000004   Code   RO            1    sec1                sections.o
    0x00000104   0x00000004   Code   RO            2    sec2                sections.o
    0x00000108   0x00000004   Code   RO            3    sec3                sections.o
    0x0000010c   0x00000004   Code   RO            4    sec4                sections.o


    Execution Region ER_2 (Base: 0x00000200, Size: 0x00000008, Max: 0x00000010, ABSOLUTE)

    Base Addr    Size         Type   Attr      Idx    E Section Name        Object

    0x00000200   0x00000004   Code   RO            5    sec5                sections.o
    0x00000204   0x00000004   Code   RO            6    sec6                sections.o
In this example:
  • For first_fit the linker first assigns all the sections it can to ER_1, then moves on to ER_2 because that is the next available region.
  • For next_fit the linker does the same as first_fit. However, when ER_1 is full it is marked as FULL and is not considered again. In this example, ER_1 is completely full. ER_2 is then considered.
  • For best_fit the linker assigns sec1 to ER_1. It then has two regions of equal priority and specificity, but ER_1 has less space remaining. Therefore, the linker assigns sec2 to ER_1, and continues assigning sections until ER_1 is full.

Example for worst_fit

This example shows the image memory map when using the worst_fit algorithm.
    Execution Region ER_1 (Base: 0x00000100, Size: 0x0000000c, Max: 0x00000010, ABSOLUTE)

    Base Addr    Size         Type   Attr      Idx    E Section Name        Object

    0x00000100   0x00000004   Code   RO            1    sec1                sections.o
    0x00000104   0x00000004   Code   RO            3    sec3                sections.o
    0x00000108   0x00000004   Code   RO            5    sec5                sections.o


    Execution Region ER_2 (Base: 0x00000200, Size: 0x0000000c, Max: 0x00000010, ABSOLUTE)

    Base Addr    Size         Type   Attr      Idx    E Section Name        Object

    0x00000200   0x00000004   Code   RO            2    sec2                sections.o
    0x00000204   0x00000004   Code   RO            4    sec4                sections.o
    0x00000208   0x00000004   Code   RO            6    sec6                sections.o
The linker first assigns sec1 to ER_1. It then has two equally specific and priority regions. It assigns sec2 to the one with the most free space, ER_2 in this example. The regions now have the same amount of space remaining, so the linker assigns sec3 to the first one that appears in the scatter file, that is ER_1.

Note

The behavior of worst_fit is the default behavior in this version of the linker, and it is the only algorithm available in earlier linker versions.
Related reference
Non-ConfidentialPDF file icon PDF versionARM DUI0377H
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