Add configure to CMake to detect GNU strerror_r

* Add getstrerror to libpsl-native
* Add Unix.GetLastPerror to CorePsPlatform

src/System.Management.Automation/CoreCLR/CorePsPlatform.cs

@@ -453,6 +453,11 @@ namespace System.Management.Automation
 
         internal static class Unix
         {
+            internal static string GetLastPerror()
+            {
+                return Unix.NativeMethods.GetStrError(Marshal.GetLastWin32Error());
+            }
+
             private static string s_userName;
             public static string UserName
             {
@@ -568,6 +573,10 @@ namespace System.Management.Automation
 
                 // C bools are 1 byte and so must be marshaled as I1
 
+                [DllImport(psLib, CharSet = CharSet.Ansi)]
+                [return: MarshalAs(UnmanagedType.LPStr)]
+                internal static extern string GetStrError(int errno);
+
                 [DllImport(psLib, CharSet = CharSet.Ansi, SetLastError = true)]
                 [return: MarshalAs(UnmanagedType.LPStr)]
                 internal static extern string GetUserName();

src/libpsl-native/.gitignore

@@ -9,4 +9,5 @@ Testing/
 test/psl-native-test
 src/libpsl-native.so
 src/libpsl-native.dylib
+src/config.h
 test/native-tests.xml

src/libpsl-native/src/CMakeLists.txt

@@ -1,3 +1,18 @@
+include(CheckCXXSourceCompiles)
+check_cxx_source_compiles(
+    "
+    #include <string.h>
+    int main()
+    {
+        char buffer[1];
+        char* c = strerror_r(0, buffer, 0);
+        (void)c;
+    }
+    "
+    HAVE_GNU_STRERROR_R)
+
+configure_file(${CMAKE_CURRENT_SOURCE_DIR}/config.h.in ${CMAKE_CURRENT_BINARY_DIR}/config.h)
+
 add_library(psl-native SHARED
   getstat.cpp
   getlstat.cpp
@@ -9,6 +24,7 @@ add_library(psl-native SHARED
   getcomputername.cpp
   getlinkcount.cpp
   getfullyqualifiedname.cpp
+  getstrerror.cpp
   isfile.cpp
   isdirectory.cpp
   issymlink.cpp

src/libpsl-native/src/config.h.in

@@ -0,0 +1 @@
+#cmakedefine HAVE_GNU_STRERROR_R 1

src/libpsl-native/src/getstrerror.cpp

@@ -0,0 +1,40 @@
+#include "getstrerror.h"
+
+#include <assert.h>
+#include <sys/types.h>
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+char* GetStrError(int errnum)
+{
+    size_t buflen = 256;
+    char* buf = (char*)calloc(buflen, sizeof(char));
+
+// Note that we must use strerror_r because plain strerror is not
+// thread-safe.
+//
+// However, there are two versions of strerror_r:
+//    - GNU:   char* strerror_r(int, char*, size_t);
+//    - POSIX: int   strerror_r(int, char*, size_t);
+//
+// The former may or may not use the supplied buffer, and returns
+// the error message string. The latter stores the error message
+// string into the supplied buffer and returns an error code.
+
+#if HAVE_GNU_STRERROR_R
+    const char* ret = strerror_r(errnum, buf, buflen);
+    assert(ret != NULL);
+    if (ret != buf)
+    {
+        // message was returned but is static, copy for return
+        strncpy(buf, ret, buflen);
+    }
+#else
+    int ret = strerror_r(errnum, buf, buflen);
+    // EINVAL: unknown error but reasonable message returned.
+    // ERANGE: too small for entire message, but still filled and null-terminated.
+    assert(ret == 0 || ret == EINVAL || ret == ERANGE);
+#endif
+    return buf;
+}

src/libpsl-native/src/getstrerror.h

@@ -0,0 +1,9 @@
+#pragma once
+
+#include "pal.h"
+
+PAL_BEGIN_EXTERNC
+
+char* GetStrError(int);
+
+PAL_END_EXTERNC

src/libpsl-native/src/pal.h

@@ -1,5 +1,7 @@
 #pragma once
 
+#include "config.h"
+
 #include <stdlib.h>
 #include <string.h>
 #include <inttypes.h>