linux-kernel - Re: [PATCH v9 6/6] riscv: Use --emit-relocs in order to move .rela.dyn in init

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Message-ID: <20230912233331.zejmknzcm5mwzzcz@google.com>
Date:   Tue, 12 Sep 2023 16:34:36 -0700
From:   Fangrui Song <maskray@...gle.com>
To:     Alexandre Ghiti <alexghiti@...osinc.com>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Björn Töpel <bjorn@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org,
        linux-kbuild@...r.kernel.org
Subject: Re: [PATCH v9 6/6] riscv: Use --emit-relocs in order to move
 .rela.dyn in init

On 2023-03-29, Alexandre Ghiti wrote:
>To circumvent an issue where placing the relocations inside the init
>sections produces empty relocations, use --emit-relocs. But to avoid
>carrying those relocations in vmlinux, use an intermediate
>vmlinux.relocs file which is a copy of vmlinux *before* stripping its
>relocations.
>
>Suggested-by: Björn Töpel <bjorn@...nel.org>
>Suggested-by: Nick Desaulniers <ndesaulniers@...gle.com>
>Signed-off-by: Alexandre Ghiti <alexghiti@...osinc.com>
>---
> arch/riscv/Makefile          |  2 +-
> arch/riscv/Makefile.postlink | 13 +++++++++++++
> arch/riscv/boot/Makefile     |  7 +++++++
> 3 files changed, 21 insertions(+), 1 deletion(-)
>
>diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
>index 860b09e409c7..7dc6904a6836 100644
>--- a/arch/riscv/Makefile
>+++ b/arch/riscv/Makefile
>@@ -8,7 +8,7 @@
>
> OBJCOPYFLAGS    := -O binary
> ifeq ($(CONFIG_RELOCATABLE),y)
>-	LDFLAGS_vmlinux += -shared -Bsymbolic -z notext -z norelro
>+	LDFLAGS_vmlinux += -shared -Bsymbolic -z notext -z norelro --emit-relocs
> 	KBUILD_CFLAGS += -fPIE
> endif
> ifeq ($(CONFIG_DYNAMIC_FTRACE),y)
>[...]

(Not subscribed.
b4 am https://lore.kernel.org/all/20230329045329.64565-7-alexghiti@rivosinc.com/
neomutt -f v9_20230329_alexghiti_introduce_64b_relocatable_kernel.mbx)

This commit 559d1e45a16dcf1542e430ea3dce9ab625be98d0 introduced --emit-relocs to arch/riscv/.
I am concerned that --emit-relocs's relocation-type-changing behavior may not be desired and
any new use could become problematic.

https://sourceware.org/bugzilla/show_bug.cgi?id=30844 "ld riscv: --emit-relocs does not retain the original relocation type"

If either -mno-relax or --no-relax is used, --emit-relocs should be fine.