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#### 6.31.18 MIPS Function Attributes

These function attributes are supported by the MIPS back end:

`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 use the following attributes to modify the behavior of an interrupt handler:

  `use_shadow_register_set`

    Assume that the handler uses a shadow register set, instead of the main general-purpose registers.

  `keep_interrupts_masked`

    Keep interrupts masked for the whole function. Without this attribute, GCC tries to reenable interrupts for as much of the function as it can.

  `use_debug_exception_return`

    Return using the `deret` instruction. Interrupt handlers that don’t have this attribute return using `eret` instead.

  You can use any combination of these attributes, as shown below:

      void __attribute__ ((interrupt)) v0 ();
      void __attribute__ ((interrupt, use_shadow_register_set)) v1 ();
      void __attribute__ ((interrupt, keep_interrupts_masked)) v2 ();
      void __attribute__ ((interrupt, use_debug_exception_return)) v3 ();
      void __attribute__ ((interrupt, use_shadow_register_set,
                           keep_interrupts_masked)) v4 ();
      void __attribute__ ((interrupt, use_shadow_register_set,
                           use_debug_exception_return)) v5 ();
      void __attribute__ ((interrupt, keep_interrupts_masked,
                           use_debug_exception_return)) v6 ();
      void __attribute__ ((interrupt, use_shadow_register_set,
                           keep_interrupts_masked,
                           use_debug_exception_return)) v7 ();

`long_call`
`near`
`far`

  These attributes specify how a particular function is called on MIPS. The attributes override the `-mlong-calls` (see MIPS Options) command-line switch. The `long_call` and `far` attributes are synonyms, and cause the compiler to always call the function by first loading its address into a register, and then using the contents of that register. The `near` attribute has the opposite effect; it specifies that non-PIC calls should be made using the more efficient `jal` instruction.

`mips16`
`nomips16`

  On MIPS targets, you can use the `mips16` and `nomips16` function attributes to locally select or turn off MIPS16 code generation. A function with the `mips16` attribute is emitted as MIPS16 code, while MIPS16 code generation is disabled for functions with the `nomips16` attribute. These attributes override the `-mips16` and `-mno-mips16` options on the command line (see MIPS Options).

  When compiling files containing mixed MIPS16 and non-MIPS16 code, the preprocessor symbol `__mips16` reflects the setting on the command line, not that within individual functions. Mixed MIPS16 and non-MIPS16 code may interact badly with some GCC extensions such as `__builtin_apply` (see Constructing Calls).

`micromips, MIPS`
`nomicromips, MIPS`

  On MIPS targets, you can use the `micromips` and `nomicromips` function attributes to locally select or turn off microMIPS code generation. A function with the `micromips` attribute is emitted as microMIPS code, while microMIPS code generation is disabled for functions with the `nomicromips` attribute. These attributes override the `-mmicromips` and `-mno-micromips` options on the command line (see MIPS Options).

  When compiling files containing mixed microMIPS and non-microMIPS code, the preprocessor symbol `__mips_micromips` reflects the setting on the command line, not that within individual functions. Mixed microMIPS and non-microMIPS code may interact badly with some GCC extensions such as `__builtin_apply` (see Constructing Calls).

`nocompression`

  On MIPS targets, you can use the `nocompression` function attribute to locally turn off MIPS16 and microMIPS code generation. This attribute overrides the `-mips16` and `-mmicromips` options on the command line (see MIPS Options).

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