6.31.2 AArch64 Function Attributes ¶

The following target-specific function attributes are available for the AArch64 target. For the most part, these options mirror the behavior of similar command-line options (see AArch64 Options), but on a per-function basis.

general-regs-only ¶

Indicates that no floating-point or Advanced SIMD registers should be used when generating code for this function. If the function explicitly uses floating-point code, then the compiler gives an error. This is the same behavior as that of the command-line option -mgeneral-regs-only.

fix-cortex-a53-835769 ¶

Indicates that the workaround for the Cortex-A53 erratum 835769 should be applied to this function. To explicitly disable the workaround for this function specify the negated form: no-fix-cortex-a53-835769. This corresponds to the behavior of the command line options -mfix-cortex-a53-835769 and -mno-fix-cortex-a53-835769.

cmodel= ¶

Indicates that code should be generated for a particular code model for this function. The behavior and permissible arguments are the same as for the command line option -mcmodel=.

strict-align ¶

Indicates that the compiler should not assume that unaligned memory references are handled by the system. The behavior is the same as for the command-line option -mstrict-align.

omit-leaf-frame-pointer ¶

Indicates that the frame pointer should be omitted for a leaf function call. To keep the frame pointer, the inverse attribute no-omit-leaf-frame-pointer can be specified. These attributes have the same behavior as the command-line options -momit-leaf-frame-pointer and -mno-omit-leaf-frame-pointer.

tls-dialect= ¶

Specifies the TLS dialect to use for this function. The behavior and permissible arguments are the same as for the command-line option -mtls-dialect=.

arch= ¶

Specifies the architecture version and architectural extensions to use for this function. The behavior and permissible arguments are the same as for the -march= command-line option.

tune= ¶

Specifies the core for which to tune the performance of this function. The behavior and permissible arguments are the same as for the -mtune= command-line option.

cpu= ¶

Specifies the core for which to tune the performance of this function and also whose architectural features to use. The behavior and valid arguments are the same as for the -mcpu= command-line option.

The above target attributes can be specified as follows:

__attribute__((target("attr-string")))
int
f (int a)
{
  return a + 5;
}

where attr-string is one of the attribute strings specified above.

Additionally, the architectural extension string may be specified on its own. This can be used to turn on and off particular architectural extensions without having to specify a particular architecture version or core. Example:

__attribute__((target("+crc+nocrypto")))
int
foo (int a)
{
  return a + 5;
}

In this example target("+crc+nocrypto") enables the crc extension and disables the crypto extension for the function foo without modifying an existing -march= or -mcpu option.

Multiple target function attributes can be specified by separating them with a comma. For example:

__attribute__((target("arch=armv8-a+crc+crypto,tune=cortex-a53")))
int
foo (int a)
{
  return a + 5;
}

is valid and compiles function foo for ARMv8-A with crc and crypto extensions and tunes it for cortex-a53.

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