On Fri, Jul 13, 2007 at 11:08:15AM +0100, Andrew Haley wrote: > > > I can work around some of the failures, but I can't really be > > > bothered: the real fix for this is EABI. > > > > Unfortunately, the EABI won't fix this either. In its native form it > > supported neither forced unwinding nor _Unwind_Backtrace; we added > > forced unwinding for the benefit of NPTL (though we're still talking > > to ARM intermittently about its semantics). But no one's tried to > > make _Unwind_Backtrace work yet, and it's not clear how to. To me > > anyway. > > Interesting. Presumably there is enough information in the unwinder > data to do it? If it's technically impossible to do a simple > backtrace then I have to wonder what the point of the EABI is.
The data is there, but it's not structured the right way. In .eh_frame unwinding, there's a standard format to define saved registers and an augmentation to define the language-specific data and the personality routine which understands that language-specific data. In ARM EABI unwinding, the personality routine is responsible for reading the saved register data as well as the language specific data. So the core unwinder (_Unwind_* in libgcc) is limited in what it can do by the flags accepted by the personality routines. There are several standard formats defined by the EHABI. GCC only ever uses those. But we might not have our own implementations of the personality routines, so we can't ABI-conformantly pass them invalid flags. We play a little loose with this for forced unwinding and let ourselves sleep at night since we proposed standardization language for them to ARM :-) However, for the standard table formats and personality routines, we could arrange to do backtraces anyway. It should be just a matter of a day's work or so and a little more code in the unwinder, and it would work with all GCC-compiled code with unwind info. More: http://www.arm.com/pdfs/ehabi.pdf -- Daniel Jacobowitz CodeSourcery -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]
