coregrind/link_tool_exe_linux.in

#! @PERL@

# This script handles linking the tool executables on Linux,
# statically and at an alternative load address.
#
# Linking statically sidesteps all sorts of complications to do with
# having two copies of the dynamic linker (valgrind's and the
# client's) coexisting in the same process.  The alternative load
# address is needed because Valgrind itself will load the client at
# whatever address it specifies, which is almost invariably the
# default load address.  Hence we can't allow Valgrind itself (viz,
# the tool executable) to be loaded at that address.
#
# Unfortunately there's no standard way to do 'static link at
# alternative address', so these link_tool_exe_*.in scripts handle
# the per-platform hoop-jumping.
#
# What we get passed here is:
#   first arg
#      the alternative load address
#   all the rest of the args
#      the gcc invocation to do the final link, that
#      the build system would have done, left to itself
#
# We just let the script 'die' if something is wrong, rather than do
# proper error reporting.  We don't expect the users to run this 
# directly.  It is only run as part of the build process, with 
# carefully constrained inputs.
#
# Linux specific complications:
#
# - need to support both old GNU ld and gold: use -Ttext= to
#   set the text segment address if that is all we have. We really
#   need -Ttext-segment. Otherwise with GNU ld sections or notes
#   (like the build-id) don't get at the desired address. But older
#   linkers only know about -Ttext, not -Ttext-segment. So configure
#   checks for us and sets FLAG_T_TEXT.
#
# - If all we have is -Ttext, then we need to pass --build-id=none
#   (that is, -Wl,--build-id=none to gcc) if it accepts it, to ensure
#   the linker doesn't add a notes section which ends up at the default
#   load address and so defeats our attempts to keep that address clear
#   for the client.  However, older linkers don't support this flag,
#   so it is tested for by configure.in and is shipped to us as part of
#   argv[2 ..].
#
# So: what we actually do:
# 
#   pass the specified command to the linker as-is, except, add
#   "-static" and "-Ttext[-segment]=<argv[1]>" to it.
#   Previously we did this by adding these options after the first
#   word of the rest of the arguments, which works in the common case
#   when it's something like "gcc". But the linker invocation itself
#   might be multiple words, say if it's "ccache gcc". So we now put
#   the new options at the end instead.
#

use warnings;
use strict;

# expect at least: alt-load-address gcc -o foo bar.o
die "Not enough arguments"
    if (($#ARGV + 1) < 5);

my $ala = $ARGV[0];
shift; # Remove $ala from @ARGV

# check for plausible-ish alt load address
die "Bogus alt-load address"
    if (length($ala) < 3 || index($ala, "0x") != 0);

my $cmd = join(" ", @ARGV, "-static -Wl,@FLAG_T_TEXT@=$ala");

#print "link_tool_exe_linux: $cmd\n";


# Execute the command:
my $r = system($cmd);

if ($r == 0) {
    exit 0;
} else {
    exit 1;
}