From: Huacai Chen <chenhuacai@kernel.org>
To: Xi Ruoyao <xry111@xry111.site>
Cc: Jinyang He <hejinyang@loongson.cn>,
WANG Xuerui <kernel@xen0n.name>,
loongarch@lists.linux.dev, LKML <linux-kernel@vger.kernel.org>,
Youling Tang <tangyouling@loongson.cn>
Subject: Re: [PATCH v7 0/5] LoongArch: Support toolchain with new relocation types
Date: Wed, 31 Aug 2022 22:40:00 +0800 [thread overview]
Message-ID: <CAAhV-H4N_XvmP9KA1M5crU44kHr33MZUVSsMY4Ugu5wQSv_LOQ@mail.gmail.com> (raw)
In-Reply-To: <bc323d8578d2f6ec580066bab181788b305ae3c3.camel@xry111.site>
On Wed, Aug 31, 2022 at 4:09 PM Xi Ruoyao <xry111@xry111.site> wrote:
>
> On Wed, 2022-08-31 at 14:58 +0800, Jinyang He wrote:
> > That's right. Also I am wondering why new toolchain produce .got* in
> > kernel. It's unneeded. In the past, gcc create la.global and parsed
> > to la.pcrel by gas, and kernel works well. Now it seems we lost this
> > feature in gcc. I checked the x86 asm code just now. And some info
> > follows,
> >
> > LoongArch64, ./net/ipv4/udp_diag.s, *have reloc hint*
> > pcalau12i $r4,%got_pc_hi20(udplite_table)
> > ld.d $r4,$r4,%got_pc_lo12(udplite_table)
> > b udp_dump
> >
> > x86_64, ./net/ipv4/udp_diag.s
> > movq $udplite_table, %rdi
> > jmp udp_dump
> >
> > It seems related to -fno-PIE and -cmodel=kernel on x86_64.
> > Hope new gcc with this feature now.
>
> On x86_64 -mcmodel=kernel means "all code and data are located in [-
> 2GiB, 0) range. We actually don't strictly require a "high" range as
> we're mostly a PIC-friendly architecture: note that we use a
> pcalau12i/addi.d pair for PIC addressing in [PC-2GiB, PC+2GiB, and a
> lu12i.w/addi.d pair for "non-PIC" addressing in [-2GiB, 2GiB), both are
> 2-insn sequence.
>
> If we can put the main kernel image and the modules in one 2GiB VA
> range, we can avoid GOT completely. But it's not possible for now
> because main kernel image is loaded in XKPRANGE but the modules are in
> XKVRANGE. So the best we can achieve before implementing
> CONFIG_RELOCATION is using GOT in modules, and avoid GOT in the main
> kernel image (with a new code model in GCC, which will benefit both the
> kernel and statically linked executables).
Emmm, can you implement this new code model in the near future?
Huacai
>
> --
> Xi Ruoyao <xry111@xry111.site>
> School of Aerospace Science and Technology, Xidian University
>
next prev parent reply other threads:[~2022-08-31 14:40 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-30 10:48 [PATCH v7 0/5] LoongArch: Support toolchain with new relocation types Xi Ruoyao
2022-08-30 10:48 ` [PATCH v7 1/5] LoongArch: Add CONFIG_AS_HAS_EXPLICIT_RELOCS Xi Ruoyao
2022-08-30 10:48 ` [PATCH v7 2/5] LoongArch: Adjust symbol addressing for CONFIG_AS_HAS_EXPLICIT_RELOCS Xi Ruoyao
2022-08-30 10:48 ` [PATCH v7 3/5] LoongArch: Define ELF relocation types added in v2.00 ABI Xi Ruoyao
2022-08-30 10:48 ` [PATCH v7 4/5] LoongArch: Support PC-relative relocations in modules Xi Ruoyao
2022-08-30 12:59 ` kernel test robot
2022-08-30 10:48 ` [PATCH v7 5/5] LoongArch: Support R_LARCH_GOT_PC* " Xi Ruoyao
2022-08-30 13:05 ` [PATCH v7 0/5] LoongArch: Support toolchain with new relocation types Huacai Chen
2022-08-30 14:48 ` Xi Ruoyao
2022-08-30 16:37 ` WANG Xuerui
2022-08-31 5:44 ` Huacai Chen
2022-08-31 6:10 ` Xi Ruoyao
2022-08-31 6:58 ` Jinyang He
2022-08-31 8:08 ` Xi Ruoyao
2022-08-31 14:40 ` Huacai Chen [this message]
2022-08-31 15:14 ` Xi Ruoyao
2022-09-01 2:17 ` Huacai Chen
2022-09-01 2:26 ` Xi Ruoyao
2022-09-06 0:32 ` Xi Ruoyao
2022-09-06 1:52 ` Huacai Chen
2022-09-06 4:26 ` Xi Ruoyao
2022-09-06 4:43 ` Huacai Chen
2022-09-06 5:01 ` Xi Ruoyao
2022-09-06 5:57 ` Huacai Chen
2022-09-06 7:18 ` Ard Biesheuvel
2022-09-06 8:20 ` Huacai Chen
2022-09-06 8:59 ` Huacai Chen
2022-09-06 10:16 ` Ard Biesheuvel
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