From: Xi Ruoyao <xry111@xry111.site>
To: Youling Tang <tangyouling@loongson.cn>, loongarch@lists.linux.dev
Cc: linux-kernel@vger.kernel.org, WANG Xuerui <kernel@xen0n.name>,
Huacai Chen <chenhuacai@kernel.org>,
Jinyang He <hejinyang@loongson.cn>,
Lulu Cheng <chenglulu@loongson.cn>
Subject: Re: [PATCH v4 0/4] LoongArch: Support new relocation types
Date: Sat, 30 Jul 2022 10:52:54 +0800 [thread overview]
Message-ID: <00eede4b1380888a500f74b1e818bb25a550632b.camel@xry111.site> (raw)
In-Reply-To: <1d0783b87bda3e454a111862fcc5b5faffcb16b0.camel@xry111.site>
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
--
Xi Ruoyao <xry111@xry111.site>
School of Aerospace Science and Technology, Xidian University
next prev parent reply other threads:[~2022-07-30 2:52 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 [this message]
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
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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