syscall.c

#define _GNU_SOURCE
#include <errno.h>
#include <getopt.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/syscall.h>
#include <unistd.h>

#include "syscall.h"

#define NARG 7

uintptr_t arg[NARG];
char buf[BUFSIZ];

const syscall_table_t syscall_table = {
#include "tab.h"
};

int main(int argc, char **argv) {
  int oflag = 0, vflag = 0, opt;
  size_t ncount = 0;
  while ((opt = getopt(argc, argv, "ovln:h")) != -1) {
    switch (opt) {
    case 'o':
      oflag = 1;
      break;
    case 'v':
      vflag = 1;
      break;
    case 'n':
      ncount = (size_t)strtoull(optarg, NULL, 0);
      break;
    case 'l':
      for (int i = 0; syscall_table[i].name; i++) {
        fprintf(stdout, "%s\n", syscall_table[i].name);
      }
      return 0;
    case 'h':
      fprintf(stderr, "usage: \tsyscall [-o -v -l -n bytes] entry [args; "
                      "buf==8KB buffer]\n");
      fprintf(stderr, "\tsyscall write 1 hello 5\n");
      fprintf(stderr, "\tsyscall -o read 0 buf 5\n");
      fprintf(stderr, "\tsyscall -o getcwd buf 100\n");
      return 0;
    default:
      return -1;
    }
  }

  if (optind >= argc) {
    fprintf(stderr, "No entry specified\n");
    return -1;
  }

  for (int i = 0; i < NARG && i < argc - optind; i++) {
    arg[i] = parse(argv[i + optind]);
  }

  for (int i = 0; syscall_table[i].name; i++) {
    if (strcmp(syscall_table[i].name, (char *)arg[0]) == 0) {
      long rc = syscall(syscall_table[i].code, arg[1], arg[2], arg[3], arg[4], arg[5], arg[6]);
      if (rc == -1) {
        perror("syscall");
      }

      if (oflag) {
        if (ncount > 0)
          fwrite(buf, 1, ncount, stdout);
        else
          printf("%s", buf);
      }
      if (vflag)
        fprintf(stderr, "Syscall return: %ld\n", rc);
      return rc == -1 ? 1 : 0;
    }
  }
  fprintf(stderr, "Invalid syscall entry: %s\n", (char *)arg[0]);
  return -1;
}

uintptr_t parse(char *s) {
  char *t;
  uintptr_t l;

  if (strcmp(s, "buf") == 0)
    return (uintptr_t)buf;
  if (strcmp(s, "stdin") == 0)
    return STDIN_FILENO;
  if (strcmp(s, "stdout") == 0)
    return STDOUT_FILENO;
  if (strcmp(s, "stderr") == 0)
    return STDERR_FILENO;

  l = strtoull(s, &t, 0);
  if (t > s && *t == 0) {
    return (uintptr_t)l;
  }

  return (uintptr_t)s;
}