is there any use of attribute ((interrupt)) for riscv compilers?

October 14, 2022

we can read here that the interrupt attribute keyword is use for ARM, AVR, CR16, Epiphany, M32C, M32R/D, m68k, MeP, MIPS, RL78, RX and Xstormy16.

does it have any impact on riscv compilation using riscv32-***-elf-gcc compilers?

>Solution :

There is a separate page for RISC-V which claims it works. You can find it here. Also you could probably verify it by compiling code with and without the attribute set.

I don’t have riscv32 toolchain installed, but i managed to verify it using the riscv64 toolchain. You should reproduce the same steps using the riscv32 toolchain to make sure it works.

Using a simple test.c file:

__attribute__((interrupt))
void test() {}

Compiling it with riscv64-linux-gnu-gcc -c -o test.o test.c and disassembling with riscv64-linux-gnu-objdump -D -j.text test.o we can see it generates mret instruction at the end of the function:

   0:   1141                    addi    sp,sp,-16
   2:   e422                    sd  s0,8(sp)
   4:   0800                    addi    s0,sp,16
   6:   0001                    nop
   8:   6422                    ld  s0,8(sp)
   a:   0141                    addi    sp,sp,16
   c:   30200073                mret

After removing the interrupt attribute the instruction changes to regular ret. According to this SO answer this seems like correct behaviour.