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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

Manually placing __at sections

7.2.8 Manually placing __at sections

You can have direct control over the placement of __at sections, if required.

You can use the standard section-placement rules to place __at sections when using the --no_autoat command-line option.

Note:

You cannot use __at section placement with position-independent execution regions.

The following example shows the placement of read-only sections .ARM.__at_0x2000 and the read-write section .ARM.__at_0x4000. Load and execution regions are not created automatically in manual mode. An error is produced if an __at section cannot be placed in an execution region.

The following example shows the placement of the variables in C or C++ code:

// place the RO variable in a section called .ARM.__at_0x2000
const int foo __attribute__((section(".ARM.__at_0x2000"))) = 100;
// place the RW variable in a section called .ARM.__at_0x4000
int bar __attribute__((section(".ARM.__at_0x4000")));

The following scatter file shows how to place __at sections manually:

LR1 0x0
{
    ER_RO 0x0 0x2000
    {
        *(+RO)               ; .ARM.__at_0x0000 is selected by +RO
    }
    ER_RO2 0x2000
    {
        *(.ARM.__at_0x02000)  ; .ARM.__at_0x2000 is selected by the section named
                              ; .ARM.__at_0x2000
    }
    ER2 0x4000
    {
        *(+RW, +ZI)           ; .ARM.__at_0x4000 is selected by +RW
    }
}
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