From: Huacai Chen <chenhuacai@kernel.org>
To: Youling Tang <tangyouling@loongson.cn>
Cc: Xi Ruoyao <xry111@xry111.site>,
loongarch@lists.linux.dev, LKML <linux-kernel@vger.kernel.org>,
WANG Xuerui <kernel@xen0n.name>,
Jinyang He <hejinyang@loongson.cn>,
Lulu Cheng <chenglulu@loongson.cn>
Subject: Re: [PATCH v4 0/4] LoongArch: Support new relocation types
Date: Mon, 1 Aug 2022 10:34:07 +0800 [thread overview]
Message-ID: <CAAhV-H5wSJZ2X46ySqoaJd7Z2soGcYKRNixnghmE3f3zEzyS+w@mail.gmail.com> (raw)
In-Reply-To: <7512ae16-b171-d072-674f-a6b9a5e764d6@loongson.cn>
Hi, all,
On Mon, Aug 1, 2022 at 10:16 AM Youling Tang <tangyouling@loongson.cn> wrote:
>
> Hi, Ruoyao
>
> On 07/30/2022 10:52 AM, Xi Ruoyao wrote:
> > On Sat, 2022-07-30 at 10:24 +0800, Xi Ruoyao wrote:
> >> On Sat, 2022-07-30 at 01:55 +0800, Xi Ruoyao wrote:
> >>> On Fri, 2022-07-29 at 20:19 +0800, Youling Tang wrote:
> >>>
> >>>> On 07/29/2022 07:45 PM, Xi Ruoyao wrote:
> >>>>> Hmm... The problem is the "addresses" of per-cpu symbols are
> >>>>> faked: they
> >>>>> are actually offsets from $r21. So we can't just load such an
> >>>>> offset
> >>>>> with PCALA addressing.
> >>>>>
> >>>>> It looks like we'll need to introduce an attribute for GCC to
> >>>>> make
> >>>>> an
> >>>>> variable "must be addressed via GOT", and add the attribute into
> >>>>> PER_CPU_ATTRIBUTES.
> >>>
> >>>> Yes, we need a GCC attribute to specify the per-cpu variable.
> >>>
> >>> GCC patch adding "addr_global" attribute for LoongArch:
> >>> https://gcc.gnu.org/pipermail/gcc-patches/2022-July/599064.html
> >>>
> >>> An experiment to use it:
> >>> https://github.com/xry111/linux/commit/c1d5d70
> >>
> >> Correction: https://github.com/xry111/linux/commit/c1d5d708
> >>
> >> It seems 7-bit SHA is not enough for kernel repo.
> >
> > If addr_global is rejected or not implemented (for example, building the
> > kernel with GCC 12), *I expect* the following hack to work (I've not
> > tested it because I'm AFK now). Using visibility in kernel seems
> > strange, but I think it may make some sense because the modules are some
> > sort of similar to an ELF shared object being dlopen()'ed, and our way
> > to inject per-CPU symbols is analog to ELF interposition.
> >
> > arch/loongarch/include/asm/percpu.h:
> >
> > #if !__has_attribute(__addr_global__) && defined(MODULE)
> > /* Magically remove "static" for per-CPU variables. */
> > # define ARCH_NEEDS_WEAK_PER_CPU
> > /* Force GOT-relocation for per-CPU variables. */
> > # define PER_CPU_ATTRIBUTES __attribute__((__visibility__("default")))
> > #endif
> >
> > arch/loongarch/Makefile:
> >
> > # Hack for per-CPU variables, see PER_CPU_ATTRIBUTES in
> > # include/asm/percpu.h
> > if (call gcc-does-not-support-addr-global)
> > KBUILD_CFLAGS_MODULE += -fPIC -fvisibility=hidden
> > endif
> >
> Using the old toolchain (GCC 12) can successfully load the nf_tables.ko
> module after applying the above patch.
I don't like such a hack..., can we consider using old relocation
types when building by old toolchains?
Huacai
>
> Thanks,
> Youling
>
next prev parent reply other threads:[~2022-08-01 2:34 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-29 8:38 [PATCH v4 0/4] LoongArch: Support new relocation types Xi Ruoyao
2022-07-29 8:39 ` [PATCH v4 1/4] LoongArch: Add section of GOT for kernel module Xi Ruoyao
2022-07-29 8:40 ` [PATCH v4 2/4] LoongArch: Support R_LARCH_SOP_PUSH_GPREL relocation type in " Xi Ruoyao
2022-07-29 8:41 ` [PATCH v4 3/4] LoongArch: Remove -fplt and -Wa,-mla-* from CFLAGS Xi Ruoyao
2022-07-29 8:42 ` [PATCH v4 4/4] LoongArch: Support modules with new relocation types Xi Ruoyao
2022-08-01 9:45 ` Youling Tang
2022-08-09 11:31 ` Youling Tang
2022-07-29 9:47 ` [PATCH v4 0/4] LoongArch: Support " WANG Xuerui
2022-07-29 9:49 ` Youling Tang
2022-07-29 10:18 ` Xi Ruoyao
2022-07-29 10:36 ` Xi Ruoyao
2022-07-29 11:45 ` Xi Ruoyao
2022-07-29 12:19 ` Youling Tang
2022-07-29 17:55 ` Xi Ruoyao
2022-07-30 2:24 ` Xi Ruoyao
2022-07-30 2:52 ` Xi Ruoyao
2022-07-30 6:14 ` Huacai Chen
[not found] ` <674cb3e9-d820-016b-a210-afd37ed6e25e@loongson.cn>
2022-07-30 9:51 ` Xi Ruoyao
2022-07-30 10:38 ` Huacai Chen
2022-07-31 3:07 ` Xi Ruoyao
2022-08-01 2:16 ` Youling Tang
2022-08-01 2:34 ` Huacai Chen [this message]
2022-08-01 4:31 ` Youling Tang
2022-08-01 9:55 ` Xi Ruoyao
2022-08-01 10:08 ` Jinyang He
2022-08-01 10:44 ` WANG Xuerui
2022-08-01 11:28 ` Youling Tang
2022-08-01 11:39 ` Xi Ruoyao
2022-08-01 12:09 ` Huacai Chen
2022-08-01 12:13 ` Youling Tang
[not found] ` <98efbf76-fbf3-f90b-82d4-bd2874088d05@loongson.cn>
2022-08-02 7:15 ` Xi Ruoyao
2022-08-27 13:20 ` Huacai Chen
2022-08-01 10:41 ` Huacai Chen
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