powerpc: Check for unsupported relocs when using CONFIG_RELOCATABLE
When using CONFIG_RELOCATABLE, we build the kernel as a position
independent executable. The kernel then uses a little bit of relocation
code to relocate itself. That code only deals with R_PPC64_RELATIVE
relocations though. If for some reason you use assembly constructs
such as LOAD_REG_IMMEDIATE() to load the address of a symbol, you'll
generate different kinds of relocations that won't be processed properly
and bad things will happen. (We have 2 such bugs today).
The perl script tries to filter out "known" bad ones. It's possible
that we are missing some in the case of a weak function that nobody
implements, we'll see if we get false positive and fix it.
Signed-off-by: Tony Breeds <tony@bakeyournoodle.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
diff --git a/arch/powerpc/relocs_check.pl b/arch/powerpc/relocs_check.pl
new file mode 100755
index 0000000..d257109
--- /dev/null
+++ b/arch/powerpc/relocs_check.pl
@@ -0,0 +1,56 @@
+#!/usr/bin/perl
+
+# Copyright © 2009 IBM Corporation
+
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version
+# 2 of the License, or (at your option) any later version.
+
+# This script checks the relcoations of a vmlinux for "suspicious"
+# relocations.
+
+use strict;
+use warnings;
+
+if ($#ARGV != 1) {
+ die "$0 [path to objdump] [path to vmlinux]\n";
+}
+
+# Have Kbuild supply the path to objdump so we handle cross compilation.
+my $objdump = shift;
+my $vmlinux = shift;
+my $bad_relocs_count = 0;
+my $bad_relocs = "";
+my $old_binutils = 0;
+
+open(FD, "$objdump -R $vmlinux|") or die;
+while (<FD>) {
+ study $_;
+
+ # Only look at relcoation lines.
+ next if (!/\s+R_/);
+
+ # These relocations are okay
+ next if (/R_PPC64_RELATIVE/ or /R_PPC64_NONE/ or
+ /R_PPC64_ADDR64\s+mach_/);
+
+ # If we see this type of relcoation it's an idication that
+ # we /may/ be using an old version of binutils.
+ if (/R_PPC64_UADDR64/) {
+ $old_binutils++;
+ }
+
+ $bad_relocs_count++;
+ $bad_relocs .= $_;
+}
+
+if ($bad_relocs_count) {
+ print "WARNING: $bad_relocs_count bad relocations\n";
+ print $bad_relocs;
+}
+
+if ($old_binutils) {
+ print "WARNING: You need at binutils >= 2.19 to build a ".
+ "CONFIG_RELCOATABLE kernel\n";
+}