2.7.1. Attribute Syntax¶

There are three different kinds of attributes supported by the tiarmclang compiler:

2.7.1.1. General Syntax¶

In general, an attribute can be applied to a function, variable, or type in the following ways:

attribute-specifier <function, variable, or type>

<function, variable, or type> attribute=specifier

where an attribute-specifier consists of the following parts:

__attribute__((attribute-list))

An attribute-list consists of zero or more comma-separated attributes where each attribute can be:

an attribute name that takes no arguments (like noinit or persistent),
an attribute name that expects a list of arguments enclosed in parentheses (like aligned or section). Further details about argument requirements are provided in the descriptions of those attributes that take arguments, or
empty, in which case the attribute-specifier is ignored.

An attribute-specifier can precede a variable definition:
```
__attribute__((section("my_sect"))) int my_var;
```
An attribute-specifier can be specified at the end of an uninitialized variable declaration:
```
int my_var __attribute__((section("my_sect")));
```
An attribute-specifier can be applied to an initialized variable:
```
int my_var __attribute__((section("my_sect"))) = 5;
```
The attribute-specifier in this case must precede the initializer.
An attribute-specifier can be applied to a structure member:
```
struct {
  char m1;
  int  m2 __attribute__((packed));
  int  m3;
} packed_struct = { 10, 20, 30 };
```
In this case, struct member m2 is aligned on a 1-byte boundary relative to the beginning of the struct due to the packed attribute, but m3 is aligned on a 4-byte boundary relative to the beginning of the struct.
An attribute-specifier applied to a struct type can apply to all members of the struct:
```
struct __attribute__((packed)) {
  char m1;
  int  m2;
  int  m3;
} packed_struct = { 10, 20, 30 };
```
In this case, all members of the struct are aligned on a 1-byte boundary relative to the beginning of the struct due to the packed attribute.

Multiple attributes can be applied in a single attribute-specifier:

__attribute__((noinit,location(0x100))) int noinit_location_global;