Function attributes

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Arm^® Compiler Reference Guide

Version 6.15

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B3.1 Function attributes

The __attribute__ keyword enables you to specify special attributes of variables, structure fields, functions, and types.

The keyword format is either of the following:

__attribute__((attribute1, attribute2, ...))
__attribute__((__attribute1__, __attribute2__, ...))

For example:

int my_function(int b) __attribute__((const));
static int my_variable __attribute__((__unused__));

The following table summarizes the available function attributes.

Table B3-1 Function attributes that the compiler supports, and their equivalents

Function attribute	Non-attribute equivalent
`__attribute__((alias))`	-
`__attribute__((always_inline))`	-
`__attribute__((cmse_nonsecure_call))`	-
`__attribute__((cmse_nonsecure_entry))`	-
`__attribute__((const))`	-
`__attribute__((constructor(priority)))`	-
`__attribute__((deprecated))`	-
`__attribute__((format_arg(string-index)))`	-
`__attribute__((interrupt("type")))`	-
`__attribute__((malloc))`	-
`__attribute__((naked))`	-
`__attribute__((noinline))`	`__declspec(noinline)`
`__attribute__((nomerge))`	-
`__attribute__((nonnull))`	-
`__attribute__((noreturn))`	`__declspec(noreturn)`
`__attribute__((nothrow))`	`__declspec(nothrow)`
`__attribute__((notailcall))`	-
`__attribute__((pcs("calling_convention")))`	-
`__attribute__((pure))`	-
`__attribute__((section("name")))`	-
`__attribute__((target("branch-protection=none")))`	-
`__attribute__((unused))`	-
`__attribute__((used))`	-
`__attribute__((value_in_regs))`	-
`__attribute__((visibility("visibility_type")))`	-
`__attribute__((weak))`	-
`__attribute__((weakref("target")))`	-

Usage

You can set these function attributes in the declaration, the definition, or both. For example:

void AddGlobals(void) __attribute__((always_inline));
__attribute__((always_inline)) void AddGlobals(void) {...}

When function attributes conflict, the compiler uses the safer or stronger one. For example, __attribute__((used)) is safer than __attribute__((unused)), and __attribute__((noinline)) is safer than __attribute__((always_inline)).