riscv
keywords: rv32, rv64
- ISA type:
RISC
- Endianness:
little
,big
Registers
- riscv32 =>
XLEN=32
- riscv64 =>
XLEN=64
General purpose registers
[XLEN-1:0] abi name desc
---------------------------------------------
x0 zero zero register
x1 ra return addr
x2 sp stack ptr
x3 gp global ptr
x4 tp thread ptr
x5-x7 t0-t2 temp regs
x8-x9 s0-s1 saved regs
x10-x17 a0-a7 arg regs
x18-x27 s2-s11 saved regs
x28-x31 t3-t6 temp regs
ASM skeleton
Small assembler skeleton, ready to use with following properties:
- use raw Linux syscalls (
man 2 syscall
for ABI) - no
C runtime (crt)
- gnu assembler
gas
// file: greet.S
#include <asm/unistd.h> // syscall NRs
.section .text, "ax", @progbits
.balign 4 // align code on 4byte boundary
.global _start
_start:
li a0, 2 // fd
la a1, greeting // buf
ld a2, (greeting_len) // &len
li a7, __NR_write // write(2) syscall
ecall
li a0, 42 // exit code
li a7, __NR_exit // exit(2) syscall
ecall
.balign 8 // align data on 8byte boundary
.section .rodata, "a", @progbits
greeting:
.asciz "Hi ASM-World!\n"
greeting_len:
.int .-greeting
man gcc:
file.S
assembler code that must be preprocessed.
To cross-compile and run:
> riscv64-linux-gnu-gcc -o greet greet.S -nostartfiles -nostdlib \
-Wl,--dynamic-linker=/usr/riscv64-linux-gnu/lib/ld-linux-riscv64-lp64d.so.1 \
&& qemu-riscv64 ./greet
Hi ASM-World!
Cross-compiling on
Ubuntu 20.04 (x86_64)
, paths might differ on other distributions. Explicitly specifying the dynamic linker should not be required when compiling natively on riscv.Select dynamic linker according to abi used during compile & link.