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. An optional argument is supported for the interrupt attribute which allows the interrupt mode to be described. By default GCC assumes the external interrupt controller (EIC) mode is in use, this can be explicitly set using eic. When interrupts are non-masked then the requested Interrupt Priority Level (IPL) is copied to the current IPL which has the effect of only enabling higher priority interrupts. To use vectored interrupt mode use the argument vector=[sw0|sw1|hw0|hw1|hw2|hw3|hw4|hw5], this will change the behavior of the non-masked interrupt support and GCC will arrange to mask all interrupts from sw0 up to and including the specified interrupt vector.

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. An optional argument intstack is supported to indicate that the shadow register set contains a valid stack pointer.

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 ();
void __attribute__ ((interrupt("eic"))) v8 ();
void __attribute__ ((interrupt("vector=hw3"))) v9 ();

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).