[hoc-cvs] [hoc] r408 committed - On GNUstep, clean up the stack frame chain in...

[<cod...@go...>]

Revision: 408
Author: wol...@gm...
Date: Thu Aug 20 16:09:05 2009
Log: On GNUstep, clean up the stack frame chain in
Invocation.m:callWithExceptions

When the FFI call from Haskell to callWithExceptions() is made,
%ebp contains not a stack frame link but rather some other value.
When GNUstep's NSException tries to walk the stack to generate a
stack trace, it segfaults.
Therefore, we use GCC's __builtin_frame_address to retrieve
the saved frame pointer value, save it elsewhere and reset the
stack frame link to 0 so that GNUstep's stack trace just stops
there.
It is reset to the stored value upon exit.

Fixes issue #19.


http://code.google.com/p/hoc/source/detail?r=408

Modified:
  /trunk/hoc/HOC_cbits/Invocation.m

=======================================
--- /trunk/hoc/HOC_cbits/Invocation.m	Sat Jan  5 08:46:39 2008
+++ /trunk/hoc/HOC_cbits/Invocation.m	Thu Aug 20 16:09:05 2009
@@ -8,10 +8,37 @@
  NSException *callWithExceptions(ffi_cif *cif, void (*fn)(),
                                  void *rvalue, void **avalue)
  {
+#ifdef GNUSTEP
+    // GHC messes up the stack frame chain.
+    // GNUstep generates exception stack traces on the assumption
+    // that the stack frame chain makes sense.
+    // Therefore, we move the frame pointer value left behind by
+    // GHC from its regular stack slot into a local variable and
+    // set the stack-frame link to 0 (temporarily).
+
+    void **frame = __builtin_frame_address(0);
+    void *save = *frame;
+
+    // We assume that
+    // *(void**)__builtin_frame_address(0) == __builtin_frame_address(1)
+    // which is true at least for i386, x86_64 and powerpc[64].
+    assert(save == __builtin_frame_address(1));
+
+    *frame = 0;
+#endif
+
+    NSException *exception = nil;
  	NS_DURING
  		ffi_call(cif, fn, rvalue, avalue);
  	NS_HANDLER
-		return localException;
+		exception = localException;
  	NS_ENDHANDLER
-	return nil;
-}
+
+#ifdef GNUSTEP
+    // restore old stack frame link
+    *frame = save;
+#endif
+
+	return exception;
+}
+