[PATCH] RISC-V/libgcc: Use `-fasynchronous-unwind-tables' for LIB2_DIVMOD_FUNCS

[Kito Cheng]

Hi Maciej:

LGTM, thanks for your patch!

On Sat, Aug 29, 2020 at 9:19 PM Maciej W. Rozycki via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> Use `-fasynchronous-unwind-tables' rather than `-fexceptions
> -fnon-call-exceptions' in LIB2_DIVMOD_FUNCS compilation flags so as to
> provide unwind tables for the affected functions while not pulling the
> unwinder proper, which is not required here.
>
> Beyond saving program space it fixes a RISC-V glibc build error due to
> unsatisfied `malloc' and `free' references from the unwinder causing
> link errors with `ld.so' where libgcc has been built at -O0.
>
>         libgcc/
>         * config/riscv/t-elf (LIB2_DIVMOD_EXCEPTION_FLAGS): New
>         variable.
> ---
> Hi,
>
>  As Mon, Aug 31st (a bank holiday in England) will be my last day at
> Western Digital and I won't be able to submit patches on behalf of the
> company afterwards here is a replacement change for RISC-V only in case
> the generic one discussed here:
>
> <https://gcc.gnu.org/pipermail/gcc-patches/2020-August/552327.html
>
> does not go through.  While I won't be able to submit changes I will
> continue watching the discussion and I will be able to commit either
> change once there is the final outcome, just as anyone would.
>
>  This change has passed full GCC regression testing with the
> `riscv64-linux-gnu' target, RV64/lp64d and RV32/ilp32d multilibs, using
> QEMU in the Linux user emulation mode.
>
>   Maciej
> ---
>  libgcc/config/riscv/t-elf |    2 ++
>  1 file changed, 2 insertions(+)
>
> gcc-riscv-libgcc-divmod-asynchronous-unwind-tables.diff
> Index: gcc/libgcc/config/riscv/t-elf
> ===================================================================
> --- gcc.orig/libgcc/config/riscv/t-elf
> +++ gcc/libgcc/config/riscv/t-elf
> @@ -4,3 +4,5 @@ LIB2ADD += $(srcdir)/config/riscv/save-r
>            $(srcdir)/config/riscv/div.S \
>            $(srcdir)/config/riscv/atomic.c \
>
> +# Avoid the full unwinder being pulled along with the division libcalls.
> +LIB2_DIVMOD_EXCEPTION_FLAGS := -fasynchronous-unwind-tables