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Date: Tue, 15 Sep 2009 15:57:02 +1000
From: Benjamin Herrenschmidt <benh@...nel.crashing.org>
To: linuxppc-dev list <linuxppc-dev@...abs.org>
Cc: Linux Kernel list <linux-kernel@...r.kernel.org>
Subject: [PATCH] powerpc: Check for unsupported relocs when using
CONFIG_RELOCATABLE
From: Tony Breeds <tony@...eyournoodle.com>
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@...eyournoodle.com>
Signed-off-by: Benjamin Herrenschmidt <benh@...nel.crashing.org>
---
diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
index 952a396..0101e0c 100644
--- a/arch/powerpc/Makefile
+++ b/arch/powerpc/Makefile
@@ -166,6 +166,17 @@ PHONY += $(BOOT_TARGETS)
boot := arch/$(ARCH)/boot
+ifeq ($(CONFIG_RELOCATABLE),y)
+quiet_cmd_relocs_check = CALL $<
+ cmd_relocs_check = perl $< "$(OBJDUMP)" "$(obj)/vmlinux"
+
+PHONY += relocs_check
+relocs_check: arch/powerpc/relocs_check.pl vmlinux
+ $(call cmd,relocs_check)
+
+zImage: relocs_check
+endif
+
$(BOOT_TARGETS): vmlinux
$(Q)$(MAKE) ARCH=ppc64 $(build)=$(boot) $(patsubst %,$(boot)/%,$@)
diff --git a/arch/powerpc/relocs_check.pl b/arch/powerpc/relocs_check.pl
new file mode 100755
index 0000000..215e966
--- /dev/null
+++ b/arch/powerpc/relocs_check.pl
@@ -0,0 +1,57 @@
+#!/usr/bin/perl
+
+# Copyright © 2009 IBM Corporation
+
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version
+# 2 of the License, or (at your option) any later version.
+
+# This script checks the relcoations of a vmlinux for "suspicious"
+# relocations.
+
+use strict;
+use warnings;
+
+if ($#ARGV != 1) {
+ print "$#ARGV\n";
+ 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";
+}
--
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