On Wed, Dec 26, 2018 at 7:39 AM Cherry Zhang <cherr...@google.com> wrote: > > Finally I found an ARM machine and was able to build ARM32 gcc on it, and > reproduced the failures. The Go programs aborted, in parse_lsda_header, > called from probestackmaps in the runtime startup. It seems that > _Unwind_GetLanguageSpecificData doesn't return a valid LSDA when called from > a callback from _Unwind_Backtrace. > > Reading the unwinder's source code in libgcc, it seems that a function may > have a "predefined" personality function, and in this case an ARM-specific > "compact" model is used, which doesn't use the standard LSDA. > _Unwind_GetLanguageSpecificData doesn't distinguish this and simply assumes > the "generic" model is used, i.e. not used with a "predefined" personality > function. This works fine if _Unwind_GetLanguageSpecificData is called from a > non-predefined personality function, but it doesn't work if it is called > during _Unwind_Backtrace. > > The patch below (also CL > https://go-review.googlesource.com/c/gofrontend/+/155758) will fix the > problem, by checking which model is used before calling > _Unwind_GetLanguageSpecificData. > > Alternatively, we could change _Unwind_GetLanguageSpecificData in libgcc to > returning NULL when a predefined personality function is used. > > Let me know what you think. > > Thanks, > Cherry > > diff --git a/libgo/runtime/go-unwind.c b/libgo/runtime/go-unwind.c > index f4bbfb60..388d7c70 100644 > --- a/libgo/runtime/go-unwind.c > +++ b/libgo/runtime/go-unwind.c > @@ -646,6 +646,17 @@ findstackmaps (struct _Unwind_Context *context, > _Unwind_Ptr *ip, _Unwind_Ptr *sp > _sleb128_t index; > int size; > > +#ifdef __ARM_EABI_UNWINDER__ > + { > + _Unwind_Control_Block *ucbp; > + ucbp = (_Unwind_Control_Block *) _Unwind_GetGR (context, 12); > + if (*ucbp->pr_cache.ehtp & (1u << 31)) > + // The "compact" model is used, with one of the predefined > + // personality functions. It doesn't have standard LSDA. > + return NOTFOUND_OK; > + } > +#endif > + > language_specific_data = (const unsigned char *) > _Unwind_GetLanguageSpecificData (context); >
Thanks. Committed to mainline. Ian
