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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 Placing the stack and heap with a scatter file Scatter-loading command-line options Scatter-loading images with a simple memory map Scatter-loading images with a complex memory map Root region and the initial entry point Effect of the ABSOLUTE attribute on a root region Effect of the FIXED attribute on a root region Methods of placing functions and data at specific Placing functions and data in a named section Placing __at sections at a specific address Restrictions on placing __at sections Automatically placing __at sections Manually placing __at sections Placing a key in flash memory with an __at section Example of how to explicitly place a named section Placement of unassigned sections Default rules for placing unassigned sections Command-line options for controlling the placement Prioritizing the placement of unassigned 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 Placing veneers with a scatter file Placement of CMSE veneer sections for a Secure ima Reserving an empty block of memory Characteristics of a reserved empty block of memor Example of reserving an empty block of memory Placement of Arm C and C++ library code Placing code in a root region Placing Arm C library code Placing Arm C++ library code Aligning regions to page boundaries Aligning execution regions and input sections Preprocessing a scatter file Default behavior for armclang -E in a scatter file Using other preprocessors in 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 BPABI Shared Libraries and Executables Features of the Base Platform Linking Model Linker Command-line Options Linker Steering File Command Reference Via File Syntax

Example of how to explicitly place a named section with scatter-loading

7.3 Example of how to explicitly place a named section with scatter-loading

This example shows how to place a named section explicitly using scatter-loading.

Consider the following source files:

init.c
------
int foo() __attribute__((section("INIT")));
int foo() {
  return 1;
}

int bar() {
  return 2;
}

data.c
------
const long padding=123;
int z=5;

The following scatter file shows how to place a named section explicitly:

LR1 0x0 0x10000
{
    ; Root Region, containing init code
    ER1 0x0 0x2000
    {
        init.o (INIT, +FIRST)   ; place init code at exactly 0x0
        *(+RO)                  ; rest of code and read-only data  
    }
    ; RW & ZI data to be placed at 0x400000
    RAM_RW 0x400000 (0x1FF00-0x2000)
    {
        *(+RW)
    }
    RAM_ZI +0
    {
        *(+ZI)
    }
    ; execution region at 0x1FF00
    ; maximum space available for table is 0xFF
    DATABLOCK 0x1FF00 0xFF
    {
        data.o(+RO-DATA)  ; place RO data between 0x1FF00 and 0x1FFFF
    }
}

In this example, the scatter-loading description places:

  • The initialization code is placed in the INIT section in the init.o file. This example shows that the code from the INIT section is placed first, at address 0x0, followed by the remainder of the RO code and all of the RO data except for the RO data in the object data.o.

  • All global RW variables in RAM at 0x400000.

  • A table of RO-DATA from data.o at address 0x1FF00.

The resulting image memory map is as follows:

Memory Map of the image

  Image entry point : Not specified.

  Load Region LR1 (Base: 0x00000000, Size: 0x00000018, Max: 0x00010000, ABSOLUTE)

    Execution Region ER1 (Base: 0x00000000, Size: 0x00000010, Max: 0x00002000, ABSOLUTE)

    Base Addr    Size         Type   Attr      Idx    E Section Name        Object

    0x00000000   0x00000008   Code   RO            4    INIT                init.o
    0x00000008   0x00000008   Code   RO            1    .text               init.o
    0x00000010   0x00000000   Code   RO           16    .text               data.o


    Execution Region DATABLOCK (Base: 0x0001ff00, Size: 0x00000004, Max: 0x000000ff, ABSOLUTE)

    Base Addr    Size         Type   Attr      Idx    E Section Name        Object

    0x0001ff00   0x00000004   Data   RO           19    .rodata             data.o


    Execution Region RAM_RW (Base: 0x00400000, Size: 0x00000004, Max: 0x0001df00, ABSOLUTE)

    Base Addr    Size         Type   Attr      Idx    E Section Name        Object

    0x00400000   0x00000000   Data   RW            2    .data               init.o
    0x00400000   0x00000004   Data   RW           17    .data               data.o


    Execution Region RAM_ZI (Base: 0x00400004, Size: 0x00000000, Max: 0xffffffff, ABSOLUTE)

    Base Addr    Size         Type   Attr      Idx    E Section Name        Object

    0x00400004   0x00000000   Zero   RW            3    .bss                init.o
    0x00400004   0x00000000   Zero   RW           18    .bss                data.o

            
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