powerpc: Move script to check relocations at compile time in scripts/

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/
so that other architectures can take advantage of it.

Signed-off-by: Alexandre Ghiti <alex@ghiti.fr>
Reviewed-by: Anup Patel <anup@brainfault.org>
Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)
Link: https://lore.kernel.org/r/20230329045329.64565-5-alexghiti@rivosinc.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

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)