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/*
* random_seed.c
*
* Copyright (c) 2013 Metaparadigm Pte. Ltd.
* Michael Clark <michael@metaparadigm.com>
*
* This library is free software; you can redistribute it and/or modify
* it under the terms of the MIT license. See COPYING for details.
*
*/
#include <stdio.h>
#include "config.h"
#include "random_seed.h"
#define DEBUG_SEED(s)
#if defined ENABLE_RDRAND
/* cpuid */
#if defined __GNUC__ && (defined __i386__ || defined __x86_64__)
#define HAS_X86_CPUID 1
static void do_cpuid(int regs[], int h)
{
__asm__ __volatile__(
#if defined __x86_64__
"pushq %%rbx;\n"
#else
"pushl %%ebx;\n"
#endif
"cpuid;\n"
#if defined __x86_64__
"popq %%rbx;\n"
#else
"popl %%ebx;\n"
#endif
: "=a"(regs[0]), [ebx] "=r"(regs[1]), "=c"(regs[2]), "=d"(regs[3])
: "a"(h));
}
#elif defined _MSC_VER
#define HAS_X86_CPUID 1
#define do_cpuid __cpuid
#endif
/* has_rdrand */
#if HAS_X86_CPUID
static int has_rdrand()
{
// CPUID.01H:ECX.RDRAND[bit 30] == 1
int regs[4];
do_cpuid(regs, 1);
return (regs[2] & (1 << 30)) != 0;
}
#endif
/* get_rdrand_seed - GCC x86 and X64 */
#if defined __GNUC__ && (defined __i386__ || defined __x86_64__)
#define HAVE_RDRAND 1
static int get_rdrand_seed()
{
DEBUG_SEED("get_rdrand_seed");
int _eax;
// rdrand eax
__asm__ __volatile__("1: .byte 0x0F\n"
" .byte 0xC7\n"
" .byte 0xF0\n"
" jnc 1b;\n"
: "=a" (_eax));
return _eax;
}
#endif
#if defined _MSC_VER
#if _MSC_VER >= 1700
#define HAVE_RDRAND 1
/* get_rdrand_seed - Visual Studio 2012 and above */
static int get_rdrand_seed()
{
DEBUG_SEED("get_rdrand_seed");
int r;
while (_rdrand32_step(&r) == 0);
return r;
}
#elif defined _M_IX86
#define HAVE_RDRAND 1
/* get_rdrand_seed - Visual Studio 2010 and below - x86 only */
static int get_rdrand_seed()
{
DEBUG_SEED("get_rdrand_seed");
int _eax;
retry:
// rdrand eax
__asm _emit 0x0F __asm _emit 0xC7 __asm _emit 0xF0
__asm jnc retry
__asm mov _eax, eax
return _eax;
}
#endif
#endif
#endif /* defined ENABLE_RDRAND */
/* has_dev_urandom */
#if defined (__APPLE__) || defined(__unix__) || defined(__linux__)
#include <string.h>
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>
#include <stdlib.h>
#include <sys/stat.h>
#define HAVE_DEV_RANDOM 1
static const char *dev_random_file = "/dev/urandom";
static int has_dev_urandom()
{
struct stat buf;
if (stat(dev_random_file, &buf)) {
return 0;
}
return ((buf.st_mode & S_IFCHR) != 0);
}
/* get_dev_random_seed */
static int get_dev_random_seed()
{
DEBUG_SEED("get_dev_random_seed");
int fd = open(dev_random_file, O_RDONLY);
if (fd < 0) {
fprintf(stderr, "error opening %s: %s", dev_random_file, strerror(errno));
exit(1);
}
int r;
ssize_t nread = read(fd, &r, sizeof(r));
if (nread != sizeof(r)) {
fprintf(stderr, "error short read %s: %s", dev_random_file, strerror(errno));
exit(1);
}
close(fd);
return r;
}
#endif
/* get_cryptgenrandom_seed */
#ifdef WIN32
#define HAVE_CRYPTGENRANDOM 1
#include <windows.h>
#include <wincrypt.h>
#ifndef __GNUC__
#pragma comment(lib, "advapi32.lib")
#endif
static int get_cryptgenrandom_seed()
{
DEBUG_SEED("get_cryptgenrandom_seed");
HCRYPTPROV hProvider = 0;
int r;
if (!CryptAcquireContextW(&hProvider, 0, 0, PROV_RSA_FULL, CRYPT_VERIFYCONTEXT | CRYPT_SILENT)) {
fprintf(stderr, "error CryptAcquireContextW");
exit(1);
}
if (!CryptGenRandom(hProvider, sizeof(r), (BYTE*)&r)) {
fprintf(stderr, "error CryptGenRandom");
exit(1);
}
CryptReleaseContext(hProvider, 0);
return r;
}
#endif
/* get_time_seed */
#include <time.h>
static int get_time_seed()
{
DEBUG_SEED("get_time_seed");
return (int)time(NULL) * 433494437;
}
/* json_c_get_random_seed */
int json_c_get_random_seed()
{
#if HAVE_RDRAND
if (has_rdrand()) return get_rdrand_seed();
#endif
#if HAVE_DEV_RANDOM
if (has_dev_urandom()) return get_dev_random_seed();
#endif
#if HAVE_CRYPTGENRANDOM
return get_cryptgenrandom_seed();
#endif
return get_time_seed();
}
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