10.61 __attribute__((at(address))) variable attribute

This variable attribute enables you to specify the absolute address of a variable.

The variable is placed in its own section, and the section containing the variable is given an appropriate type by the compiler:

  • Read-only variables are placed in a section of type RO.

  • Initialized read-write variables are placed in a section of type RW.

    Variables explicitly initialized to zero are placed in:

    • A section of type ZI in RVCT 4.0 and later.

    • A section of type RW (not ZI) in RVCT 3.1 and earlier. Such variables are not candidates for the ZI-to-RW optimization of the compiler.

  • Uninitialized variables are placed in a section of type ZI.

Note

GNU compilers do not support this variable attribute.

Syntax

__attribute__((at(address)))

Where:

address

is the desired address of the variable.

Restrictions

The linker is not always able to place sections produced by the at variable attribute.

The compiler faults use of the at attribute when it is used on declarations with incomplete types.

Errors

The linker gives an error message if it is not possible to place a section at a specified address.

Examples

const int x1 __attribute__((at(0x10000))) = 10; /* RO */
int x2 __attribute__((at(0x12000))) = 10; /* RW */
int x3 __attribute__((at(0x14000))) = 0; /* RVCT 3.1 and earlier: RW.
                                          * RVCT 4.0 and later: ZI. */
int x4 __attribute__((at(0x16000))); /* ZI */
Related information
Placement of __at sections at a specific address
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