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Message-ID: <aced7303ca2a4130b73cfa46d7a25c1f4812a651.camel@xry111.site>
Subject: Re: [PATCH 0/5] LoongArch: Support new relocation types
From:   Xi Ruoyao <xry111@xry111.site>
To:     loongarch@lists.linux.dev
Cc:     linux-kernel@vger.kernel.org, WANG Xuerui <kernel@xen0n.name>,
        Huacai Chen <chenhuacai@kernel.org>
Date:   Thu, 28 Jul 2022 00:46:53 +0800
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Self notes:

With "-mla-global-with-pcrel" in KBUILD_CFLAGS_KERNEL gone (even if I
don't remove it, it will be ineffective with binutils-2.40/gcc-13), the
kernel will use GOT to access the objects in other translation units.=20
It may cause a performance regression.

*If* such a performance regression is really observed, we need to change
GCC to use PC relative addressing (instead of GOT) for loading external
objects when -fno-PIC.  Such a change will benefit userspace apps as
well, *if* PC relative addressing is really faster than GOT access.

(Emphasize "if" here: I've not run any benchmarks yet.)

I'll be mostly AFK in the following one or two weeks, apologize for
possible slow respond.

On Thu, 2022-07-28 at 00:24 +0800, Xi Ruoyao wrote:
> The version 2.00 of LoongArch ELF ABI specification introduced new
> relocation types, and the development tree of Binutils and GCC has
> started to use them.=C2=A0 If the kernel is built with the latest snapsho=
t of
> Binutils or GCC, it will fail to load the modules because of unrecognized
> relocation types in modules.
>=20
> Add support for GOT and new relocation types for the module loader, so
> the kernel (with modules) can be built with the "normal" code model and
> function properly.
>=20
> Tested by building the kernel with Binutils & GCC master branch, and
> running the kernel with 35 in-tree modules loaded.
>=20
> Link: https://github.com/loongson/LoongArch-Documentation/pull/57
> Link: https://gcc.gnu.org/r13-1834
> Link: https://sourceware.org/git/?p=3Dbinutils-gdb.git;a=3Dcommit;h=3Df09=
482a
>=20
> Xi Ruoyao (5):
> =C2=A0 LoongArch: Add section of GOT for kernel module
> =C2=A0 LoongArch: Support R_LARCH_SOP_PUSH_GPREL relocation type in kerne=
l
> =C2=A0=C2=A0=C2=A0 module
> =C2=A0 LoongArch: Support relocation against _GLOBAL_OFFSET_TABLE_
> =C2=A0 LoongArch: Stop using undocumented assembler options
> =C2=A0 LoongArch: Support modules with new relocation types
>=20
> =C2=A0arch/loongarch/Makefile=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 |=C2=A0 5 +-
> =C2=A0arch/loongarch/include/asm/elf.h=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0 | 37 ++++++++++
> =C2=A0arch/loongarch/include/asm/module.h=C2=A0=C2=A0=C2=A0=C2=A0 | 23 ++=
++++
> =C2=A0arch/loongarch/include/asm/module.lds.h |=C2=A0 1 +
> =C2=A0arch/loongarch/kernel/head.S=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0 | 10 +--
> =C2=A0arch/loongarch/kernel/module-sections.c | 72 +++++++++++++++++--
> =C2=A0arch/loongarch/kernel/module.c=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0 | 94 +++++++++++++++++++++++++
> =C2=A07 files changed, 229 insertions(+), 13 deletions(-)
>=20

--=20
Xi Ruoyao <xry111@xry111.site>
School of Aerospace Science and Technology, Xidian University