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

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Date:   Wed, 29 Mar 2023 06:53:29 +0200
From:   Alexandre Ghiti <alexghiti@...osinc.com>
To:     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>,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        linux-riscv@...ts.infradead.org, linux-kbuild@...r.kernel.org
Cc:     Alexandre Ghiti <alexghiti@...osinc.com>
Subject: [PATCH v9 6/6] riscv: Use --emit-relocs in order to move .rela.dyn in init

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)
diff --git a/arch/riscv/Makefile.postlink b/arch/riscv/Makefile.postlink
index d5de8d520d3e..a46fc578b30b 100644
--- a/arch/riscv/Makefile.postlink
+++ b/arch/riscv/Makefile.postlink
@@ -15,12 +15,25 @@ quiet_cmd_relocs_check = CHKREL  $@
 cmd_relocs_check = 							\
 	$(CONFIG_SHELL) $(srctree)/arch/riscv/tools/relocs_check.sh "$(OBJDUMP)" "$(NM)" "$@"
 
+ifdef CONFIG_RELOCATABLE
+quiet_cmd_cp_vmlinux_relocs = CPREL   vmlinux.relocs
+cmd_cp_vmlinux_relocs = cp vmlinux vmlinux.relocs
+
+quiet_cmd_relocs_strip = STRIPREL $@
+cmd_relocs_strip = $(OBJCOPY)   --remove-section='.rel.*'       \
+                                --remove-section='.rel__*'      \
+                                --remove-section='.rela.*'      \
+                                --remove-section='.rela__*' $@
+endif
+
 # `@...e` prevents complaint when there is nothing to be done
 
 vmlinux: FORCE
 	@true
 ifdef CONFIG_RELOCATABLE
 	$(call if_changed,relocs_check)
+	$(call if_changed,cp_vmlinux_relocs)
+	$(call if_changed,relocs_strip)
 endif
 
 %.ko: FORCE
diff --git a/arch/riscv/boot/Makefile b/arch/riscv/boot/Makefile
index c72de7232abb..22b13947bd13 100644
--- a/arch/riscv/boot/Makefile
+++ b/arch/riscv/boot/Makefile
@@ -33,7 +33,14 @@ $(obj)/xipImage: vmlinux FORCE
 
 endif
 
+ifdef CONFIG_RELOCATABLE
+vmlinux.relocs: vmlinux
+	@ (! [ -f vmlinux.relocs ] && echo "vmlinux.relocs can't be found, please remove vmlinux and try again") || true
+
+$(obj)/Image: vmlinux.relocs FORCE
+else
 $(obj)/Image: vmlinux FORCE
+endif
 	$(call if_changed,objcopy)
 
 $(obj)/Image.gz: $(obj)/Image FORCE
-- 
2.37.2