https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103510
--- Comment #4 from ashimida <ashimida at linux dot alibaba.com> --- (In reply to Andrew Pinski from comment #3) > The only registers which are saved are the callee saved register IIRC. So > you need to know the ABI. Thanks Andrew, I saw the following description in the IA-64 C++ ABI [1]: "All registers specified as callee-saved by the base ABI are restored, as well as scratch registers GR15, GR16, GR17 and GR18 (see below). Except for those exceptions, scratch (or caller-saved) registers are not preserved, and their contents are undefined on transfer." My understanding is that the ABI states that 4 scratch registers and callee-saved need to be 'restored' before transferring conrtrol to landing pad. But AFAIK, the ABI does not specify whether unwind should 'initialize' all registers to context->reg[] at the beginning (please correct me if it's wrong). One more thing is that _Unwind_Backtrace seems to be defined in the LSB standard (I did't find its definition in the IA-64 C++ ABI). PS: The reason why I am struggling with this detail is because a similar case happened when I try to support the unwind for SCS[2] on aarch64, I found that uw_init_context_1 did not save all the registers, which would cause a crash when a ".cfi_escape 0x16, 0x12, 0x02, 0x82, 0x78" directive (means x18 -= 8) was executed, which would not happen in clang. Initializing non-call-saved registers in uw_init_context_1 can solve those issue, but i'm not sure enough if this breaks the ABI rules. [1] https://itanium-cxx-abi.github.io/cxx-abi/abi-eh.html [2] https://gcc.gnu.org/pipermail/gcc-patches/2021-November/585199.html
