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Subject[PATCH v3 3/3] arch, scripts: Add script to check relocations at compile time
Date
Relocating kernel at runtime is done very early in the boot process, so
it is not convenient to check for relocations there and react in case a
relocation was not expected.

Powerpc architecture has a script that allows to check at compile time
for such unexpected relocations: extract the common logic to scripts/
and add arch specific scripts triggered at postlink.

At the moment, powerpc and riscv architectures take advantage of this
compile-time check.

Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
---
arch/powerpc/tools/relocs_check.sh | 18 ++-------------
arch/riscv/Makefile.postlink | 36 ++++++++++++++++++++++++++++++
arch/riscv/tools/relocs_check.sh | 26 +++++++++++++++++++++
scripts/relocs_check.sh | 20 +++++++++++++++++
4 files changed, 84 insertions(+), 16 deletions(-)
create mode 100644 arch/riscv/Makefile.postlink
create mode 100755 arch/riscv/tools/relocs_check.sh
create mode 100755 scripts/relocs_check.sh

diff --git a/arch/powerpc/tools/relocs_check.sh b/arch/powerpc/tools/relocs_check.sh
index 014e00e74d2b..e367895941ae 100755
--- a/arch/powerpc/tools/relocs_check.sh
+++ b/arch/powerpc/tools/relocs_check.sh
@@ -15,21 +15,8 @@ if [ $# -lt 3 ]; then
exit 1
fi

-# Have Kbuild supply the path to objdump and nm so we handle cross compilation.
-objdump="$1"
-nm="$2"
-vmlinux="$3"
-
-# Remove from the bad relocations those that match an undefined weak symbol
-# which will result in an absolute relocation to 0.
-# Weak unresolved symbols are of that form in nm output:
-# " w _binary__btf_vmlinux_bin_end"
-undef_weak_symbols=$($nm "$vmlinux" | awk '$1 ~ /w/ { print $2 }')
-
bad_relocs=$(
-$objdump -R "$vmlinux" |
- # Only look at relocation lines.
- grep -E '\<R_' |
+${srctree}/scripts/relocs_check.sh "$@" |
# These relocations are okay
# On PPC64:
# R_PPC64_RELATIVE, R_PPC64_NONE
@@ -43,8 +30,7 @@ R_PPC_ADDR16_LO
R_PPC_ADDR16_HI
R_PPC_ADDR16_HA
R_PPC_RELATIVE
-R_PPC_NONE' |
- ([ "$undef_weak_symbols" ] && grep -F -w -v "$undef_weak_symbols" || cat)
+R_PPC_NONE'
)

if [ -z "$bad_relocs" ]; then
diff --git a/arch/riscv/Makefile.postlink b/arch/riscv/Makefile.postlink
new file mode 100644
index 000000000000..bf2b2bca1845
--- /dev/null
+++ b/arch/riscv/Makefile.postlink
@@ -0,0 +1,36 @@
+# SPDX-License-Identifier: GPL-2.0
+# ===========================================================================
+# Post-link riscv pass
+# ===========================================================================
+#
+# Check that vmlinux relocations look sane
+
+PHONY := __archpost
+__archpost:
+
+-include include/config/auto.conf
+include scripts/Kbuild.include
+
+quiet_cmd_relocs_check = CHKREL $@
+cmd_relocs_check = \
+ $(CONFIG_SHELL) $(srctree)/arch/riscv/tools/relocs_check.sh "$(OBJDUMP)" "$(NM)" "$@"
+
+# `@true` prevents complaint when there is nothing to be done
+
+vmlinux: FORCE
+ @true
+ifdef CONFIG_RELOCATABLE
+ $(call if_changed,relocs_check)
+endif
+
+%.ko: FORCE
+ @true
+
+clean:
+ @true
+
+PHONY += FORCE clean
+
+FORCE:
+
+.PHONY: $(PHONY)
diff --git a/arch/riscv/tools/relocs_check.sh b/arch/riscv/tools/relocs_check.sh
new file mode 100755
index 000000000000..baeb2e7b2290
--- /dev/null
+++ b/arch/riscv/tools/relocs_check.sh
@@ -0,0 +1,26 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0-or-later
+# Based on powerpc relocs_check.sh
+
+# This script checks the relocations of a vmlinux for "suspicious"
+# relocations.
+
+if [ $# -lt 3 ]; then
+ echo "$0 [path to objdump] [path to nm] [path to vmlinux]" 1>&2
+ exit 1
+fi
+
+bad_relocs=$(
+${srctree}/scripts/relocs_check.sh "$@" |
+ # These relocations are okay
+ # R_RISCV_RELATIVE
+ grep -F -w -v 'R_RISCV_RELATIVE'
+)
+
+if [ -z "$bad_relocs" ]; then
+ exit 0
+fi
+
+num_bad=$(echo "$bad_relocs" | wc -l)
+echo "WARNING: $num_bad bad relocations"
+echo "$bad_relocs"
diff --git a/scripts/relocs_check.sh b/scripts/relocs_check.sh
new file mode 100755
index 000000000000..137c660499f3
--- /dev/null
+++ b/scripts/relocs_check.sh
@@ -0,0 +1,20 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+# Get a list of all the relocations, remove from it the relocations
+# that are known to be legitimate and return this list to arch specific
+# script that will look for suspicious relocations.
+
+objdump="$1"
+nm="$2"
+vmlinux="$3"
+
+# Remove from the possible bad relocations those that match an undefined
+# weak symbol which will result in an absolute relocation to 0.
+# Weak unresolved symbols are of that form in nm output:
+# " w _binary__btf_vmlinux_bin_end"
+undef_weak_symbols=$($nm "$vmlinux" | awk '$1 ~ /w/ { print $2 }')
+
+$objdump -R "$vmlinux" |
+ grep -E '\<R_' |
+ ([ "$undef_weak_symbols" ] && grep -F -w -v "$undef_weak_symbols" || cat)
--
2.20.1
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