Message-ID: <CANXhq0qN-SsC=iO_5gAea=FqQqztmVUHaGxE5Z2me0h10jBU+Q@mail.gmail.com>
Date: Wed, 24 Apr 2024 14:44:35 +0800
From: Zong Li <zong.li@...ive.com>
To: Charlie Jenkins <charlie@...osinc.com>
Cc: paul.walmsley@...ive.com, palmer@...belt.com, aou@...s.berkeley.edu, 
	schwab@...e.de, linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Revert "riscv: disable generation of unwind tables"

On Tue, Apr 23, 2024 at 3:14 AM Charlie Jenkins <charlie@...osinc.com> wrote:
>
> On Tue, Apr 16, 2024 at 09:31:38AM +0800, Zong Li wrote:
> > This reverts commit 2f394c0e7d1129a35156e492bc8f445fb20f43ac.
> >
> > RISC-V has supported the complete relocation types in module loader by
> > '8fd6c5142395 ("riscv: Add remaining module relocations")'.
> > Now RISC-V port can enable unwind tables in case eh_frame parsing is
> > needed.
> >
> > Signed-off-by: Zong Li <zong.li@...ive.com>
> > ---
> >  arch/riscv/Makefile | 3 ---
> >  1 file changed, 3 deletions(-)
> >
> > diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
> > index 5b3115a19852..9216bf8a2691 100644
> > --- a/arch/riscv/Makefile
> > +++ b/arch/riscv/Makefile
> > @@ -94,9 +94,6 @@ ifeq ($(CONFIG_CMODEL_MEDANY),y)
> >       KBUILD_CFLAGS += -mcmodel=medany
> >  endif
> >
> > -# Avoid generating .eh_frame sections.
> > -KBUILD_CFLAGS += -fno-asynchronous-unwind-tables -fno-unwind-tables
> > -
>
> There are a lot of orphaned sections created by this, which throws a lot
> of warnings. These warnings will only be present on GCC-13+ since
> -fno-asynchronous-unwind-tables was a default before GCC-13.
>
> The .eh_frame orphaned sections can be resolved by including
>
> .eh_frame : {*(.eh_frame)}
>
> in arch/riscv/kernel/vmlinux.lds.S. arm64 places it in the init section,
> but outside init_data and init_text, so right after the .alternative
> definition seems like a good place.
>
> .init.eh_frame sections in drivers/firmware/efi/libstub also complain
> about being orphaned, and other architectures have disabled unwind
> tables for that compilation unit, so -fno-unwind-tables and
> -fno-asynchronous-unwind-tables should be added to
> drivers/firmware/efi/libstub/Makefile for riscv.
>
> This also causes the resulting image (with defconfig) to increase from
> 22M to 24M. There are currently no users of unwind tables in riscv so
> this should be hidden behind a config. arm64 uses this config as:
>
> # Avoid generating .eh_frame* sections.
> ifneq ($(CONFIG_UNWIND_TABLES),y)
> KBUILD_CFLAGS   += -fno-asynchronous-unwind-tables -fno-unwind-tables
> KBUILD_AFLAGS   += -fno-asynchronous-unwind-tables -fno-unwind-tables
> else
> KBUILD_CFLAGS   += -fasynchronous-unwind-tables
> KBUILD_AFLAGS   += -fasynchronous-unwind-tables
> endif
>
> Using this same config name for riscv would allow riscv to use the
> standard .eh_frame code introduced in
> https://lore.kernel.org/linux-arm-kernel/20221027155908.1940624-2-ardb@kernel.org/.
>
> This config is only enabled if some other config selects it in arm64,
> but riscv does not contain any users so maybe this config can be left
> unselected until there is a user of unwind tables in riscv.
>

Hi Charlie,
Thanks a lot for the tips and information, I will use gcc-13+ to
verify the next patch.

> - Charlie
>
> >  # The RISC-V attributes frequently cause compatibility issues and provide no
> >  # information, so just turn them off.
> >  KBUILD_CFLAGS += $(call cc-option,-mno-riscv-attribute)
> > --
> > 2.17.1
> >
> >
> > _______________________________________________
> > linux-riscv mailing list
> > linux-riscv@...ts.infradead.org
> > http://lists.infradead.org/mailman/listinfo/linux-riscv

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