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#### 6.33.25 RISC-V Function Attributes

These function attributes are supported by the RISC-V back end:

`naked`

  This attribute allows the compiler to construct the requisite function declaration, while allowing the body of the function to be assembly code. The specified function will not have prologue/epilogue sequences generated by the compiler. Only basic `asm` statements can safely be included in naked functions (see Basic Asm). While using extended `asm` or a mixture of basic `asm` and C code may appear to work, they cannot be depended upon to work reliably and are not supported.

`interrupt`

  Use this attribute to indicate that the specified function is an interrupt handler. The compiler generates function entry and exit sequences suitable for use in an interrupt handler when this attribute is present.

  You can specify the kind of interrupt to be handled by adding an optional parameter to the interrupt attribute like this:

      void f (void) __attribute__ ((interrupt ("user")));

  Permissible values for this parameter are `user`, `supervisor`, and `machine`. If there is no parameter, then it defaults to `machine`.

`riscv_vector_cc`

  Use this attribute to force the function to use the vector calling convention variant.

      void foo() __attribute__((riscv_vector_cc));
      [[riscv::vector_cc]] void foo(); // For C++11 and C23

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

`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, in addtion, it also support extension enablement list, a list of extension name and prefixed with `+`, like `arch=+zba` means enable `zba` extension. Multiple extension can be enabled by separating them with a comma. For example: `arch=+zba,+zbb`.

`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.

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

    __attribute__((target("arch=+zba,+zbb;tune=rocket")))
    int
    foo (int a)
    {
      return a + 5;
    }

is valid and compiles function `foo` with `zba` and `zbb` extensions and tunes it for `rocket`.

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