qemu-user binfmt risc-v

README.md

Compile qemu-binfmt-wrapper.c with QEMU_RISCV_BINDIR set to the bin directory qemu-riscv is installed in, and name the binary /run/binfmt/riscv64. Then riscv.conf in /etc/binfmt.d on a systemd system will have qemu-user interpret all riscv64 binaries, including respecting setuid bit. On non-systemd you'll need to add the binfmt registration some other way.

qemu-binfmt-wrapper.c

#include <unistd.h>
#include <string.h>
#include <stdio.h>
#include <sys/auxv.h>

int main(int argc,char ** argv) {
  int fd = (int) getauxval(AT_EXECFD);
  size_t sz = snprintf(NULL, 0, "/proc/self/fd/%d", fd) + 1;
  char fn[sz];
  snprintf(fn, sz, "/proc/self/fd/%d", fd);

  char * realArgv[argc + 2];
  realArgv[0] = "qemu-riscv64";
  realArgv[1] = "-0";
  realArgv[2] = argv[2];
  realArgv[3] = fn;
  memcpy(realArgv + 4, argv + 3, (argc - 3) * sizeof argv[0]);
  realArgv[argc + 1] = NULL;

  execv(QEMU_RISCV_BINDIR "/qemu-riscv64", realArgv);
  perror("Running qemu-riscv64");
  return -1;
}

riscv.conf

:riscv64:M::\x7f\x45\x4c\x46\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\xf3\x00:\xff\xff\xff\xff\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\xff\xff:/run/binfmt/riscv64:PC