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

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Message-ID: <CAAhV-H6RqKT0OiVhZqJr9Tts-4JuH-oPNAc66q6fTcqdi7jAQw@mail.gmail.com>
Date:   Tue, 6 Sep 2022 16:59:21 +0800
From:   Huacai Chen <chenhuacai@...nel.org>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     Xi Ruoyao <xry111@...111.site>, 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

On Tue, Sep 6, 2022 at 4:20 PM Huacai Chen <chenhuacai@...nel.org> wrote:
>
> On Tue, Sep 6, 2022 at 3:18 PM Ard Biesheuvel <ardb@...nel.org> wrote:
> >
> > On Tue, 6 Sept 2022 at 06:43, Huacai Chen <chenhuacai@...nel.org> wrote:
> > >
> > > 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. :)
> > >
> >
> > I don't mind changing the stable tag at this point - I don't have
> > anything queued up on top of it at the moment.
> >
> > But I don't see the actual patch: please send me the delta patch that
> > you want to apply, and I will update it. Then, you can rebase your
> > v6.1 tree on top of it.
> OK, Ruoyao, please send a patch to change the efistub cflags. Thank you.
Oh, I think you needn't send, just showing the diff to Ard is OK. :)

diff --git a/drivers/firmware/efi/libstub/Makefile
b/drivers/firmware/efi/libstub/Makefile
index 8931ed24379e..8c1225b92492 100644
--- a/drivers/firmware/efi/libstub/Makefile
+++ b/drivers/firmware/efi/libstub/Makefile
@@ -27,7 +27,7 @@ cflags-$(CONFIG_ARM)          := $(subst
$(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \
 cflags-$(CONFIG_RISCV)         := $(subst
$(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \
                                   -fpic
 cflags-$(CONFIG_LOONGARCH)     := $(subst
$(CC_FLAGS_FTRACE),,$(KBUILD_CFLAGS)) \
-                                  -fpic
+                                  -fpie

 cflags-$(CONFIG_EFI_GENERIC_STUB) += -I$(srctree)/scripts/dtc/libfdt

Huacai
>
> Huacai