folly/string: better strerror_r detection

Summary:
There are two variants of `strerror_r` function, one returns
`int`, and another returns `char*`. Selecting proper version using
preprocessor macros portably is extremely hard.

For example, on Android function signature depends on `__USE_GNU` and
`__ANDROID_API__` macros (https://git.io/fjBBE).

So we are using C++ overloading trick: we pass a pointer of
`strerror_r` to `invoke_strerror_r` function, and C++ compiler
selects proper function.

Reviewed By: yfeldblum

Differential Revision: D15484722

fbshipit-source-id: fc0bd45fa67dc401631ffc185c9fad231e4a48a0

CMake/FollyConfigChecks.cmake

@@ -191,18 +191,6 @@ check_cxx_source_compiles("
   FOLLY_USE_LIBSTDCPP
 )
 
-check_cxx_source_runs("
-  #include <string.h>
-  #include <errno.h>
-  int main(int argc, char** argv) {
-    char buf[1024];
-    buf[0] = 0;
-    int ret = strerror_r(ENOMEM, buf, sizeof(buf));
-    return ret;
-  }"
-  FOLLY_HAVE_XSI_STRERROR_R
-)
-
 check_cxx_source_runs("
   #include <stdarg.h>
   #include <stdio.h>

CMake/folly-config.h.cmake

@@ -61,7 +61,6 @@
 #cmakedefine FOLLY_HAVE_WCHAR_SUPPORT 1
 #cmakedefine FOLLY_HAVE_EXTRANDOM_SFMT19937 1
 #cmakedefine FOLLY_USE_LIBCPP 1
-#cmakedefine FOLLY_HAVE_XSI_STRERROR_R 1
 #cmakedefine HAVE_VSNPRINTF_ERRORS 1
 
 #cmakedefine FOLLY_USE_SYMBOLIZER 1

folly/String.cpp

@@ -460,6 +460,45 @@ std::string hexDump(const void* ptr, size_t size) {
   return os.str();
 }
 
+// There are two variants of `strerror_r` function, one returns
+// `int`, and another returns `char*`. Selecting proper version using
+// preprocessor macros portably is extremely hard.
+//
+// For example, on Android function signature depends on `__USE_GNU` and
+// `__ANDROID_API__` macros (https://git.io/fjBBE).
+//
+// So we are using C++ overloading trick: we pass a pointer of
+// `strerror_r` to `invoke_strerror_r` function, and C++ compiler
+// selects proper function.
+
+FOLLY_MAYBE_UNUSED
+static fbstring invoke_strerror_r(
+    int (*strerror_r)(int, char*, size_t),
+    int err,
+    char* buf,
+    size_t buflen) {
+  // Using XSI-compatible strerror_r
+  int r = strerror_r(err, buf, buflen);
+
+  // OSX/FreeBSD use EINVAL and Linux uses -1 so just check for non-zero
+  if (r != 0) {
+    return to<fbstring>(
+        "Unknown error ", err, " (strerror_r failed with error ", errno, ")");
+  } else {
+    return buf;
+  }
+}
+
+FOLLY_MAYBE_UNUSED
+static fbstring invoke_strerror_r(
+    char* (*strerror_r)(int, char*, size_t),
+    int err,
+    char* buf,
+    size_t buflen) {
+  // Using GNU strerror_r
+  return strerror_r(err, buf, buflen);
+}
+
 fbstring errnoStr(int err) {
   int savedErrno = errno;
 
@@ -484,21 +523,9 @@ fbstring errnoStr(int err) {
   } else {
     result.assign(buf);
   }
-#elif FOLLY_HAVE_XSI_STRERROR_R || defined(__APPLE__)
-
-  // Using XSI-compatible strerror_r
-  int r = strerror_r(err, buf, sizeof(buf));
-
-  // OSX/FreeBSD use EINVAL and Linux uses -1 so just check for non-zero
-  if (r != 0) {
-    result = to<fbstring>(
-        "Unknown error ", err, " (strerror_r failed with error ", errno, ")");
-  } else {
-    result.assign(buf);
-  }
 #else
-  // Using GNU strerror_r
-  result.assign(strerror_r(err, buf, sizeof(buf)));
+  // Using any strerror_r
+  result.assign(invoke_strerror_r(strerror_r, err, buf, sizeof(buf)));
 #endif
 
   return result;