C: code snippets

eprintf.c

#include <stdarg.h>
#include <string.h>
#include <errno.h>

/* eprintf: print error message and exit */
void eprintf(char *fmt, ...) {
  va_list args;

  fflush(stdout);
  if (progname() != NULL)
    fprintf(stderr, "%s: ", progname());

  va_start(args, fmt);
  vfprintf(stderr, fmt, args);
  va_end(args);

  if (fmt[0] != '\0' && fmt[strlen(fmt) - 1] == ':')
    fprintf(stderr, " %s", stderror(errno));

  fprintf(stderr, "\n");
  exit(2); /* conventional value for failed execution */
}

gia.c

/*
 * gcc inline assembly example
 */
#include <stdio.h>

int main() {
        unsigned long esp;
        unsigned long ebp;
        //get esp and ebp
        __asm__ (//".att_syntax\n\t"
                 "movq %%rsp, %0\n\t"
                 "movq %%rbp, %1\n\t"
                 : "=r"(esp), "=r"(ebp)
                 :
                 : "memory");

        printf("current stack pointer is 0x%lx, stack frame pointer 0x%lx\n",
               esp, ebp);

        //get return value
        unsigned long ret_pc;
        __asm__ ("movq 8(%%rbp), %0\n\t"
                 : "=r"(ret_pc)
                 :);
        printf("return address is 0x%lx\n", ret_pc);
}

vmcall.c

/*
 * vmcall at domU(HVM) using gcc inline assembly
 * this example works on Intel machine
 */
#define VMCALL ".byte 0x0f,0x01,0xc1"

// push vmcall number and return value into eax, no argument
static inline long hypercall0(unsigned int nr)
{
        long ret;
        asm volatile(KVM_HYPERCALL
                     : "=a"(ret)
                     : "a"(nr)
                     : "memory");
        return ret;
}

// add one argument, storing in rdi
static inline long kvm_hypercall1(unsigned int nr, unsigned long p1)
{
        long ret;
        asm volatile(KVM_HYPERCALL
                     : "=a"(ret)
                     : "a"(nr), "b"(p1)
                     : "memory");
  return ret;
}