linux

RISC-V (RV64G) assembly examples on linux

Examples

• simple main (./100.main)
• system call (./110.system_call)
• library call (./120.libc_call)
• basic operations (./300.operation)
• control flow (./400.control_flow)
• sync (./700.sync), sync_parts (./710.sync_parts)
• multi-threads (./750.multi)

How to try

• Assemble (generate binary)

  $ make -f ../Makefile  <sample>
  

• Execute

  $ ./<sample>
  or
  $ qemu-riscv64 ./<sample>
  

• Disassemble (for full object)

  $ make -f ../Makefile  <sample>.disasm  | less
  (search "main>" in `less` command)
  

• Disassemble (for .S only)

  $ make -f ../Makefile  <sample>.o.disasm
  

• Step execution with gdb

  $ make -f ../Makefile  <sample>
  $ gdb ./<sample>
  (gdb) layout asm
  (gdb) layout regs
  (gdb) break main
  (gdb) run
  (gdb) stepi
    :
  (gdb) quit
  
  

• Step execution with qemu and gdb

  • on first terminal for qemu:

  $ qemu-riscv64 -g 1234 ./<sample>
  

  • on second terminal for gdb:

  $ riscv64-unknown-linux-gnu-gdb ./<sample>
  (gdb) layout asm
  (gdb) layout regs
  (gdb) target remote localhost:1234
  (gdb) break main
  (gdb) continue
  (gdb) stepi
    :
  (gdb) quit
  

References

• RISC-V

  • The RISC-V Instruction Set Manual Volume I: Unprivileged ISA
  • RISC-V Assembly Programmer's Manual

• Linux

  • Linux kernel; arch/riscv

• glibc

  • glibc
    • sysdeps/unix/sysv/linux/riscv

• RISC-V ABI

  • RISC-V ELF psABI specification

• System call ABI

  • syscall(2) - Linux manual page

• GCC

  • GCC online documentation

• GNU assembler and linker

  • Documentation for binutils

Further information

Calling convention

• System call

  • a7, a0, a1, a2, a3, a4, a5 -> a0, a1

• Funcation call

  • a0, a1, a2, a3, a4, a5, a6, a7 -> a0, a1

• see:

  • RISC-V ELF psABI Document
  • glibc's sysdeps/unix/sysv/linux/riscv/syscall.c

Tool installation on ubuntu (x86)

• Cross assembler (RISC-V GNU Compiler Toolchain)

  Build with https://github.com/riscv/riscv-gnu-toolchain

• QEMU User space emulator

  apt install qemu-user