auto import from //depot/cupcake/@135843
diff --git a/libc/string/strerror_r.c b/libc/string/strerror_r.c
new file mode 100644
index 0000000..f43d417
--- /dev/null
+++ b/libc/string/strerror_r.c
@@ -0,0 +1,163 @@
+/* $OpenBSD: strerror_r.c,v 1.6 2005/08/08 08:05:37 espie Exp $ */
+/* Public Domain <marc@snafu.org> */
+
+#define sys_siglist _sys_siglist
+
+#include <errno.h>
+#include <limits.h>
+#include <signal.h>
+#include <string.h>
+
+typedef struct {
+ int code;
+ const char* msg;
+} CodeString;
+
+static const char*
+__code_string_lookup( const CodeString* strings,
+ int code )
+{
+ int nn = 0;
+
+ for (;;)
+ {
+ if (strings[nn].code == 0)
+ break;
+
+ if (strings[nn].code == code)
+ return strings[nn].msg;
+
+ nn++;
+ }
+ return NULL;
+}
+
+
+static const CodeString _sys_error_strings[] =
+{
+#define __BIONIC_ERRDEF(x,y,z) { y, z },
+#include <sys/_errdefs.h>
+ { 0, NULL }
+};
+
+static size_t
+__digits10(unsigned int num)
+{
+ size_t i = 0;
+
+ do {
+ num /= 10;
+ i++;
+ } while (num != 0);
+
+ return i;
+}
+
+static int
+__itoa(int num, int sign, char *buffer, size_t start, size_t end)
+{
+ size_t pos;
+ unsigned int a;
+ int neg;
+
+ if (sign && num < 0) {
+ a = -num;
+ neg = 1;
+ }
+ else {
+ a = num;
+ neg = 0;
+ }
+
+ pos = start + __digits10(a);
+ if (neg)
+ pos++;
+
+ if (pos < end)
+ buffer[pos] = '\0';
+ else
+ return ERANGE;
+ pos--;
+ do {
+ buffer[pos] = (a % 10) + '0';
+ pos--;
+ a /= 10;
+ } while (a != 0);
+ if (neg)
+ buffer[pos] = '-';
+ return 0;
+}
+
+
+int
+strerror_r(int errnum, char *strerrbuf, size_t buflen)
+{
+ int save_errno;
+ int len, ret = 0;
+ const char* msg;
+
+ save_errno = errno;
+ msg = __code_string_lookup( _sys_error_strings, errnum );
+ if (msg != NULL) {
+ len = strlcpy(strerrbuf, msg, buflen);
+ if ((size_t)len >= buflen)
+ ret = ERANGE;
+ } else {
+ len = strlcpy(strerrbuf, "Unknown error: ", buflen);
+ if ((size_t)len >= buflen)
+ ret = ERANGE;
+ else {
+ int ret = __itoa(errnum, 1, strerrbuf, len, buflen);
+
+ if (ret == 0)
+ ret = EINVAL;
+ }
+ }
+ return ret;
+}
+
+#if 0
+static const CodeString _sys_signal_strings[] =
+{
+#define SIGDEF(x,y,z) { y, z },
+#include <sys/_sigdefs.h>
+};
+
+
+static int
+__num2string(int num, int sign, int setid, char *buf, size_t buflen,
+ char * list[], size_t max, const char *def)
+{
+ int ret = 0;
+ size_t len;
+
+ if (0 <= num && num < max) {
+ len = strlcpy(buf, def, buflen);
+ if (len >= buflen)
+ ret = ERANGE;
+ } else {
+ len = strlcpy(buf, def, buflen);
+ if (len >= buflen)
+ ret = ERANGE;
+ else {
+ ret = __itoa(num, sign, buf, len, buflen);
+ if (ret == 0)
+ ret = EINVAL;
+ }
+ }
+
+ return ret;
+}
+
+
+
+#define USIGPREFIX "Unknown signal: "
+
+char *
+__strsignal(int num, char *buf)
+{
+ __num2string(num, 0, 2, buf, NL_TEXTMAX, (char **)sys_siglist, NSIG,
+ USIGPREFIX);
+ return buf;
+}
+#endif