Re: Porting to Darwin

Hi Brian,
If you are pushing ebx in MacroAssembler::enter() this will very
likely cause problems. When the VM starts executing Smalltalk code
(either native nmethod code or interpreted code) is starts by calling
the StubRoutines call delta function generated in
StubRoutines::generate_call_delta(). This starts by calling masm-
>enter() and then pushes the frame pointers from the last delta (ie.
Smalltalk) frame that it was executing in the current process. If you
have changed masm->enter() to push ebx then these pointers will not be
in the expected locations. Additionally, you will be pushing ebx for
every delta method invocation which is almost certainly unnecessary.

A better approach would be to preserve ebx after the other registers
in the generated call_delta and restore it in the companion
_return_from_delta the code for which is generated by the same
generate_call_delta method. I have patched the generation code to do
this. I was going to attach it to this message, but it seems Google
doesn't want to let me, so I am including the contents of the patch
(it's quite small) at the end of this message. I applied this locally
within my Windows environment and everything continues to work. Let me
know if you have any luck with this.

BTW the reason that the easyunit tests pass is that none of them
execute any Smalltalk code. At the moment, they test very specific
behaviours within the VM itself. Over time I would expect us to expand
the coverage, possibly including the execution of Smalltalk code, but
we are not there yet.

From the stack trace I see that you have created a new os_ module for
darwin. You should make sure that the os::platform_class_name() still
returns "UnixPlatform". This is used in the startup code to specify
the platform class to bind to the global "Platform" in the system
dictionary. This acts as a hook for all platform-specific code in the
image (well it will do in the future, for now it just hooks in the
file access code). You will need to be using libc 6 or have a link
libc.so.6 that points to your libc.so, which cannot be a linker script
(as it sometimes is in linux).

Regards, Steve

Patch contents below. Beware of line wrapping.

Index: stubRoutines.cpp
===================================================================
--- stubRoutines.cpp	(revision 139)
+++ stubRoutines.cpp	(working copy)
@@ -823,6 +823,7 @@

   masm->pushl(edi);	// save registers for C calling convetion
   masm->pushl(esi);
+  masm->pushl(ebx);

   // reset last Delta frame
   masm->reset_last_Delta_frame();
@@ -862,7 +863,8 @@
   masm->movl(Address((int)&have_nlr_through_C,
relocInfo::external_word_type), 0);

  masm->bind(_return);
-  masm->leal(esp, Address(ebp, -4*oopSize));
+  masm->leal(esp, Address(ebp, -5*oopSize));
+  masm->popl(ebx);
   masm->popl(esi);	// restore registers for C calling convetion
   masm->popl(edi);
   masm->popl(Address((int)&last_Delta_sp,
relocInfo::external_word_type)); // reset _last_Delta_sp



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