On Wed, Jun 13, 2001 at 10:50:54PM -0700, Ian Lance Taylor wrote:
> "H . J . Lu" <hjl@lucon.org> writes:
>
> > In the MIPS gas, there is
> >
> > case M_JAL_A:
>
> Not the relevant bit of code, not that it matters much. The
> instruction
> jal $31,$25
> will be handled by the M_JAL_1 case in gas/config/tc-mips.c.
>
> > Does anyone have any suggestions how to fix it?
>
> Traditional MIPS assemblers try to make life easier by doing this sort
> of translation. Modern MIPS compilers sidestep the translation
> because they can do better. In this case gcc evidently needs to do
> better in order to makes it exception handling model work. gcc should
> generate a jalr instruction, and should restore the GP register
> itself.
>
> (I suppose that it would be theoretically possible for gas to
> recognize labels of the special form $LEHEn. But that seems quite
> dreadful and quite fragile.)
The more I look at the problem, the more I doubt DAWRF2 exception will
ever work with the SVR4 MIPS ABI without the full support from gcc. The
problem is GP is a caller saved register in the SVR4 MIPS ABI. So every
caller has to do
call foo
restore gp
Given a piece of C++ code:
try
{
foo (...);
.....
}
catch (...)
{
}
When foo () throws an exception, it is gcc who has to make sure that
GP gets properly restored. Is there a way to teach the gcc exception
code that GP is a caller saved register?
BTW, in IRIX 6, GP is changed to callee saved so that it is not a
problem.
H.J.
