[LLVMdev] Any plans to add LLVM support for ARM EH EABI ?

[Renato Golin]

On 27 September 2010 18:44, Anton Korobeynikov <anton at korobeynikov.info> wrote:
>> Is it safe to say the MC work provides a (new) foundation for
>> implementing ARM EH? Or, is providing ARM EH independent of the ARM-MC
>> work?
> The latter. MC stuff helps somehow though.

Hi Anton,

What would be the best way to go on implementing EHABI exceptions in MC?

I got LLVM to lower the tables in the correct sections by changing
ARMMCAsmInfo and ARMISelLowering and LoweringObjectFile, but the
format is completely different and the personality routines get lost.
I could spend some time making it fit in DwarfException, but that's
clearly the wrong way...

I've noticed that DwarfException is using AsmPrinter directly, which
uses MCStreamer and, supposedly, can print ASM and Obj formats. But
there is no way to override that (say, by creating a ARMException
class, derived from the same parent class) and add it to AsmPrinter.

  if (MAI->doesSupportExceptionHandling())
    DE = new DwarfException(this);

Not only the object is private, there's no way to set it, and it's
called DwarException when it actually lowers both Dwarf and SjLj
modes. I propose a change to make ExceptionHandling a virtual class,
with DwarfException, SjLjException and ARMException deriving from it,
and the choice to create the DE object (above) be on the exception
type that is already in MCAsmInfo.

  ExceptionHandling* EH;
  switch (MAI->getExceptionHandlingType()) {
  case ExceptionHandling::SjLj:
    EH = new SjLjException(this); break;
  case ExceptionHandling::Dwarf:
    EH = new DwarfException(this); break;
  case ExceptionHandling::ARM:
    EH = new ARMException(this); break;
  }


Also, TargetLoweringObjectFile assumes the sections are *always*
called "gcc_except_table" and "eh_frame", which is clearly not true in
EHABI. That should also be extended to work across different ABIs, so
ARMException would get the correct sections. (should be easy just to
add new sections, though).

Does this make sense?

-- 
cheers,
--renato

PS: Shouldn't AsmPrinter be called MCPrinter now?