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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

Placing __at sections at a specific address

7.2.5 Placing __at sections at a specific address

You can give a section a special name that encodes the address where it must be placed.

To place a section at a specific address, use the function or variable attribute __attribute__((section("name"))) with the special name .ARM.__at_address.

To place ZI data at a specific address, use the variable attribute __attribute__((section("name"))) with the special name .bss.ARM.__at_address

address is the required address of the section. The compiler normalizes this address to eight hexadecimal digits. You can specify the address in hexadecimal or decimal. Sections in the form of .ARM.__at_address are referred to by the abbreviation __at.

The following example shows how to assign a variable to a specific address in C or C++ code:

// place variable1 in a section called .ARM.__at_0x8000
int variable1 __attribute__((section(".ARM.__at_0x8000"))) = 10;

Note:

The name of the section is only significant if you are trying to match the section by name in a scatter file. Without overlays, the linker automatically assigns __at sections when you use the --autoat command-line option. This option is the default. If you are using overlays, then you cannot use --autoat to place __at sections.
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