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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>
This commit is contained in:
Tony Breeds 2009-09-14 19:57:02 +00:00 committed by Benjamin Herrenschmidt
parent ad08587e5d
commit 144ef909c0
2 changed files with 67 additions and 0 deletions
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11
arch/powerpc/Makefile
View File

@ -164,6 +164,17 @@ 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)/%,$@)

56
arch/powerpc/relocs_check.pl Executable file
View File

@ -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";
}