unix: guard against clobbering errno in uv__free()

Libuv expects that free() does not clobber errno.  The system allocator
honors that assumption but custom allocators may not be so careful.

PR-URL: https://github.com/libuv/libuv/pull/837
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>

src/unix/freebsd.c

@@ -292,7 +292,7 @@ int uv_cpu_info(uv_cpu_info_t** cpu_infos, int* count) {
 
   size = sizeof(cpuspeed);
   if (sysctlbyname("hw.clockrate", &cpuspeed, &size, NULL, 0)) {
-    SAVE_ERRNO(uv__free(*cpu_infos));
+    uv__free(*cpu_infos);
     return -errno;
   }
 
@@ -301,7 +301,7 @@ int uv_cpu_info(uv_cpu_info_t** cpu_infos, int* count) {
    */
   size = sizeof(maxcpus);
   if (sysctlbyname(maxcpus_key, &maxcpus, &size, NULL, 0)) {
-    SAVE_ERRNO(uv__free(*cpu_infos));
+    uv__free(*cpu_infos);
     return -errno;
   }
 
@@ -314,8 +314,8 @@ int uv_cpu_info(uv_cpu_info_t** cpu_infos, int* count) {
   }
 
   if (sysctlbyname(cptimes_key, cp_times, &size, NULL, 0)) {
-    SAVE_ERRNO(uv__free(cp_times));
-    SAVE_ERRNO(uv__free(*cpu_infos));
+    uv__free(cp_times);
+    uv__free(*cpu_infos);
     return -errno;
   }
 

src/unix/openbsd.c

@@ -247,7 +247,7 @@ int uv_cpu_info(uv_cpu_info_t** cpu_infos, int* count) {
   which[1] = HW_CPUSPEED;
   size = sizeof(cpuspeed);
   if (sysctl(which, 2, &cpuspeed, &size, NULL, 0)) {
-    SAVE_ERRNO(uv__free(*cpu_infos));
+    uv__free(*cpu_infos);
     return -errno;
   }
 
@@ -258,7 +258,7 @@ int uv_cpu_info(uv_cpu_info_t** cpu_infos, int* count) {
     which[2] = i;
     size = sizeof(info);
     if (sysctl(which, 3, &info, &size, NULL, 0)) {
-      SAVE_ERRNO(uv__free(*cpu_infos));
+      uv__free(*cpu_infos);
       return -errno;
     }
 

src/uv-common.c

@@ -22,10 +22,11 @@
 #include "uv.h"
 #include "uv-common.h"
 
-#include <stdio.h>
 #include <assert.h>
+#include <errno.h>
 #include <stdarg.h>
 #include <stddef.h> /* NULL */
+#include <stdio.h>
 #include <stdlib.h> /* malloc */
 #include <string.h> /* memset */
 
@@ -75,7 +76,14 @@ void* uv__malloc(size_t size) {
 }
 
 void uv__free(void* ptr) {
+  int saved_errno;
+
+  /* Libuv expects that free() does not clobber errno.  The system allocator
+   * honors that assumption but custom allocators may not be so careful.
+   */
+  saved_errno = errno;
   uv__allocator.local_free(ptr);
+  errno = saved_errno;
 }
 
 void* uv__calloc(size_t count, size_t size) {