On 23/05/11 16:52, Nathan Sidwell wrote: > This patch fixes an interoperability issue with code generated by ARM's > EABI compiler. > > Unlike the generic C++ ABI, which always catches pointers by value, > ARM's ABI only catches pointers by value when there's the possibility of > derived->base conversion happening. The ARM __cxa_type_matcher can > return one of 3 values to indicate the three possibilities. GCC was > returning the success value when a pointer matched exactly, but > returning the pointer by value. This is incompatible with EABI > compliant code, which expects a reference to the thrown pointer in such > cases. > > However, we cannot simply change the GCC type matcher to return a > reference in such cases, as then it will be incompatible with existing > GCC-compiled code. GCC compiled code expects the pointer value at the > landing pad, ARM-compiled code expects a reference to the pointer > value. Hence ARM-compiled code (usually) inserts an additional > dereference. > > Note that the compiler generating the catching code, specifies the > personality routine (unwinder), but the code doing the type-matching > could come from any compliant library. > > In discussion with ARM, I developed the attached patch, which changes > __cxa_type_match to return the succeeded_with_ptr_to_base enum value > whenever a pointer is caught (rather than only when a pointer-to-derived > is converted to a pointer-to-base). This value indicates to the (ARM) > unwinding machinery that the pointer value is being returned. And makes > the type matcher work with the ARM unwinder. We do not change the > conditions under which _cxa_type_match performs the pointer indirection. > > At the other side of the interface, we have to make GCC's implementation > of the EABI unwinder work with an ARM-provided type matcher. Here, the > unwinder notes the return value from _cxa_match_type, and inserts an > additional indirection by using a spare field in the barrier_cache > structure. Fortunately GCC-generated code doesn't use the common > unwinder, but uses a gnu personality routine, which is unchanged. > > This patch results has been tested for arm-linux, and independently > tested by ARM with mixed RVCT-generated code confirming the defect has > been fixed. > > ok? > > nathan > > > arm-eh.patch > > > 2011-05-23 Nathan Sidwell <nat...@codesourcery.com> > > gcc/ > * config/arm/unwind-arm.c (enum __cxa_type_match_result): New. > (cxa_type_match): Correct declaration. > (__gnu_unwind_pr_common): Reconstruct > additional indirection when __cxa_type_match returns > succeeded_with_ptr_to_base. > > libstdc++/ > * libsupc++/eh_arm.c (__cxa_type_match): Construct address of > thrown object here. Return succeded_with_ptr_to_base for all > pointer cases. >
OK. R.
