set up errno passing from syscalls

emcc

@@ -1000,6 +1000,10 @@ try:
   if js_opts:
     shared.Settings.RUNNING_JS_OPTS = 1
 
+  shared.Settings.EXPORTED_FUNCTIONS += ['___errno_location'] # so FS can report errno back to C
+  if not shared.Settings.NO_EXIT_RUNTIME:
+    shared.Settings.EXPORTED_FUNCTIONS += ['_fflush'] # to flush the streams on FS quit
+
   shared.Settings.EMSCRIPTEN_VERSION = shared.EMSCRIPTEN_VERSION
   shared.Settings.OPT_LEVEL = opt_level
   shared.Settings.DEBUG_LEVEL = debug_level

src/library.js

@@ -5780,19 +5780,20 @@ LibraryManager.library = {
     {{{ cDefine('EOWNERDEAD') }}}: 'Previous owner died',
     {{{ cDefine('ESTRPIPE') }}}: 'Streams pipe error',
   },
-  __errno_state: 0,
-  __setErrNo__deps: ['__errno_state'],
-  __setErrNo__postset: '___errno_state = Runtime.staticAlloc(4); {{{ makeSetValue("___errno_state", 0, 0, "i32") }}};',
+  __setErrNo__deps: ['__errno_location'],
   __setErrNo: function(value) {
-    // For convenient setting and returning of errno.
-    {{{ makeSetValue('___errno_state', '0', 'value', 'i32') }}};
+    if (___setErrNo.loc === undefined) {
+      if (Module["___errno_location"]) {
+        ___setErrNo.loc = Module["___errno_location"]();
+      } else {
+        ___setErrNo.loc = 0; // no __errno_location, so errno is inaccessible from C code; no need to set it
+      }
+    }
+    if (___setErrNo.loc) {
+      {{{ makeSetValue('___setErrNo.loc', '0', 'value', 'i32') }}};
+    }
     return value;
   },
-  __errno_location__deps: ['__setErrNo'],
-  __errno_location: function() {
-    return ___errno_state;
-  },
-  __errno: '__errno_location',
 
   // ==========================================================================
   // sys/resource.h

src/library_syscall.js

@@ -379,6 +379,10 @@ mergeInto(LibraryManager.library, {
 #if SYSCALL_DEBUG
     Module.printErr('syscall! ' + [which, SYSCALLS.getFromCode(which)]);
 #endif
+    function handleSyscallFSError(e) { // syscalls return a negative number which is errno; libc calls then return just -1
+      if (typeof FS === 'undefined' || !(e instanceof FS.ErrnoError)) abort(e);
+      return -e.errno;
+    }
     switch (which) {
       case 4: { // write
         var fd = get(), buf = get(), count = get();
@@ -390,8 +394,7 @@ mergeInto(LibraryManager.library, {
         try {
           return FS.write(stream, {{{ makeGetSlabs('ptr', 'i8', true) }}}, buf, count);
         } catch (e) {
-          FS.handleFSError(e);
-          return -1;
+          return handleSyscallFSError(e);
         }
       }
       case 5: { // open
@@ -401,8 +404,7 @@ mergeInto(LibraryManager.library, {
           var stream = FS.open(pathname, flags, mode);
           return stream.fd;
         } catch (e) {
-          FS.handleFSError(e);
-          return -1;
+          return handleSyscallFSError(e);
         }
       }
       case 6: { // close
@@ -416,8 +418,7 @@ mergeInto(LibraryManager.library, {
           FS.close(stream);
           return 0;
         } catch (e) {
-          FS.handleFSError(e);
-          return -1;
+          return handleSyscallFSError(e);
         }
       }
       case 38: { // rename
@@ -428,8 +429,7 @@ mergeInto(LibraryManager.library, {
           FS.rename(old_path, new_path);
           return 0;
         } catch (e) {
-          FS.handleFSError(e);
-          return -1;
+          return handleSyscallFSError(e);
         }
       }
       case 39: { // mkdir
@@ -443,8 +443,7 @@ mergeInto(LibraryManager.library, {
           FS.mkdir(path, mode, 0);
           return 0;
         } catch (e) {
-          FS.handleFSError(e);
-          return -1;
+          return handleSyscallFSError(e);
         }
       }
       case 54: { // ioctl
@@ -476,8 +475,7 @@ mergeInto(LibraryManager.library, {
           try {
             var curr = FS.read(stream, {{{ makeGetSlabs('ptr', 'i8', true) }}}, ptr, len);
           } catch (e) {
-            FS.handleFSError(e);
-            return -1;
+            return handleSyscallFSError(e);
           }
           if (curr < 0) return -1;
           ret += curr;
@@ -499,8 +497,7 @@ mergeInto(LibraryManager.library, {
           try {
             var curr = FS.write(stream, {{{ makeGetSlabs('ptr', 'i8', true) }}}, ptr, len);
           } catch (e) {
-            FS.handleFSError(e);
-            return -1;
+            return handleSyscallFSError(e);
           }
           if (curr < 0) return -1;
           ret += curr;

src/settings.js

@@ -284,7 +284,7 @@ var NO_BROWSER = 0; // If set, disables building in browser support using the Br
 var NODE_STDOUT_FLUSH_WORKAROUND = 1; // Whether or not to work around node issues with not flushing stdout. This
                                       // can cause unnecessary whitespace to be printed.
 
-var EXPORTED_FUNCTIONS = ['_main', '_malloc', '_fflush'];
+var EXPORTED_FUNCTIONS = ['_main', '_malloc'];
                                     // Functions that are explicitly exported. These functions are kept alive
                                     // through LLVM dead code elimination, and also made accessible outside of
                                     // the generated code even after running closure compiler (on "Module").
@@ -295,8 +295,6 @@ var EXPORTED_FUNCTIONS = ['_main', '_malloc', '_fflush'];
                                     // without keeping it there, you are in effect removing it).
                                     //
                                     // malloc should always be here, as it is used for internal allocations.
-                                    // fflush is optional; it is needed to be able to flush stdout/stderr
-                                    // during shutdown
 
 var EXPORT_ALL = 0; // If true, we export all the symbols. Note that this does *not* affect LLVM, so it can
                     // still eliminate functions as dead. This just exports them on the Module object.