virtual-syscall-perf-comparison.c

#include <stdlib.h>
#include <asm/unistd.h>
#include <sys/wait.h>
#include <sys/time.h>
#include <time.h>

long __syscall(int syscallno, long arg1, long arg2, long arg3, long arg4, long arg5, long arg6);


int main(int argc, char * argv[]) {

  argc;

  if (argc == 2) {
      for (int i = 0 ; i < 1000000 ; i++) {
          struct timeval t;
          gettimeofday(&t, NULL);
      }
  } else {
      for (int i = 0 ; i < 1000000 ; i++) {
          struct timeval t;
          __syscall(__NR_gettimeofday, (long)&t, 0L, 0L, 0L, 0L, 0L);
      }
  }

  return 0;
}

asm(".pushsection .text, \"ax\", @progbits\n"

    "__syscall:"
    ".internal __syscall\n"
    ".globl __syscall\n"
    ".type __syscall, @function\n"
#if defined(__x86_64__)
  "movq %rdi, %rax\n"     /* place syscall number into %rax */
  "movq %rsi, %rdi\n"     /* shift arg1 - arg5 */
  "movq %rdx, %rsi\n"
  "movq %rcx, %rdx\n"
  "movq %r8, %r10\n"
  "movq %r9, %r8\n"
  "movq 8(%rsp),%r9\n"    /* arg6 is on the stack */
  "syscall\n"             /* do the system call */
  "ret\n"                 /* return to caller */
#else
#error Unsupported target platform
#endif
    ".size __syscall, .-__syscall\n"
    ".popsection\n");