linux-kernel - Re: [PATCH v7 0/5] LoongArch: Support toolchain with new relocation types

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Message-ID: <CAAhV-H7LjkY+XAzGs2K3544+CGOztCd4V8BuSjMJwZCgfBLDow@mail.gmail.com>
Date:   Tue, 6 Sep 2022 12:43:34 +0800
From:   Huacai Chen <chenhuacai@...nel.org>
To:     Xi Ruoyao <xry111@...111.site>, Ard Biesheuvel <ardb@...nel.org>
Cc:     Jinyang He <hejinyang@...ngson.cn>,
        WANG Xuerui <kernel@...0n.name>, loongarch@...ts.linux.dev,
        LKML <linux-kernel@...r.kernel.org>,
        Youling Tang <tangyouling@...ngson.cn>
Subject: Re: [PATCH v7 0/5] LoongArch: Support toolchain with new relocation types

Hi, Ruoyao,

On Tue, Sep 6, 2022 at 12:27 PM Xi Ruoyao <xry111@...111.site> wrote:
>
> On Tue, 2022-09-06 at 09:52 +0800, Huacai Chen wrote:
> > >   cflags-$(CONFIG_LOONGARCH)     := $(subst $(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \
> > > -                                  -fpic
> > > +                                  -fpie
> > >
> > >   cflags-$(CONFIG_EFI_GENERIC_STUB) += -I$(srctree)/scripts/dtc/libfdt
> > >
> > > (Some explanation: -fpic does not only mean "generate position-
> > > independent code", but "generate position-independent code *suitable for
> > > use in a shared library*".  On LoongArch -mdirect-extern-access cannot
> > > work for a shared library so the "-fpic -mdirect-extern-access"
> > > combination is rejected deliberately.)
> > >
> > > Not sure how to submit these changes properly...  Do you prefer me to
> > > send V8 of this series or a single patch on top of your tree on GitHub?
>
> > Don't need V8, I will squash it into the previous patch myself. But
> > can we keep efistub as is?
>
> No, we can't allow -mdirect-extern-access -fpic on LoongArch because
> without copy relocation such a combination just does not make sense (i.
> e. we cannot find a sensible way to handle such a combination in GCC).
> So such a combination will cause GCC refuse to run.
>
> Note that -fpic/-fPIC is "position-independent code *suitable for
> use in a shared library*", while -fpie/-fPIE is more like just
> "position-independent code".  The names of those options are confusing.
> (When -fpic was invented first time, people mostly believed "PIC had
> been only for shared libraries", so it's named -fpic instead of -shlib
> or something.)  IMO in the EFI stub for other ports, -fpie should be
> used instead of -fpic as well because the EFI stub is not similar to a
> shared library in any means.
You are right, but I guess that Ard doesn't want to squash the efistub
change into the LoongArch efistub support patch. :)

Huacai
>
> --
> Xi Ruoyao <xry111@...111.site>
> School of Aerospace Science and Technology, Xidian University
>