Re: IA64 EH

[Andrew Macleod <amacleod at cygnus dot com>]

>> Andrew --
>> 
>>   I see that you checked in the IA64 EH stuff.  Congratulations!  (I

Andrew Haley did the work to clean up the code and actually checked it
in, so he deserves the credit for that. (No small feat!) Otherwise it'd 
probably still be sitting on my harddrive.

>>   We should make a decision as to whether or not we want to use the
>> IA64-style exception handling on other platforms or not.  There's no
>> backwards compatibility issue here beacuse we're breaking the ABI in
>> the next release anyhow -- and removing support for the old ABI.  So,
>> the decision is only: a) does that make sense, and b) how hard is it.
>> We won't get a second chance; if we do want to do this, we want to do
>> it now.
>> 

from rth:

>> On Fri, May 26, 2000 at 09:21:32AM +0200, Martin v. Loewis wrote:
>> > > No.  The IA-64 bits that were checked in only affect unwinding.
>> > > The format that Intel chose is extremely IA-64 specific, and has
>> > > no real advantage over dwarf2 at all.

Yeah, its very ia64 specific. Its more compact in the object, but it 
would require a new set of unwind opcode definitions tailored for each target,
and it is also distasteful (IMO) in that it generates the unwind info
in the assembler instead of the compiler. Dwarf2 is more generic, so
its seems more preferable for porting activity. 

>> > 
>> > I guess a different way to phrase Mark's question is: 
>> > 
>> > a) Can the new C++ EH ABI
>> >    (http://reality.sgi.com/dehnert_engr/cxx/abi-eh.html) be
>> >    implemented on top of the dwarf2 unwinding information?
>> 
>> Yes, for the exact same reason: dwarf2 only affects the actual
>> stack unwinding, which the document you mention assumes by reference
>> from the Intel IA-64 manuals.  What's being described there is
>> the interface between the program and the unwinding runtime.
>> 

I believe Jason Merrill has a slightly modified version of that 
which he was hoping/planning to suggest as the EH ABI. Its quite similar,
but with a couple of enhancements.  I'll let him comment on it 
since I haven't looked at it for a while.

Andrew