Hi, sorry, I forgot to X-Debbugs-CC the reproducible builds mailing list. Fixing this now with forwarding the message I sent to #1011191.
Thanks! cheers, josch Forwarded message from Johannes Schauer Marin Rodrigues (2022-05-18 07:26:02): > Package: dpkg > Version: 1.21.7 > Severity: wishlist > Tags: patch > X-Debbugs-Cc: jo...@debian.org > > Hi, > > when cross compiling, one property of the build system that can > influence the contents of the generate binary packages is whether or not > the host architecture can be executed. While some platforms can natively > execute others (like amd64 can execute i386), other combinations are > more surprising. When installing the qemu-user-static package on a > system with binfmt-support, then foreign architecture binaries for all > architectures qemu supports will suddenly become executable. This is > especially tricky because this will also transparently affect chroot > builds with sbuild and neither schroot nor unshare isolation can prevent > the emulation from happening. The only ways to stop automatic emulation > are uninstalling qemu-user-static on the outside of the build chroot, > writing 0 to /proc/sys/fs/binfmt_misc/qemu-$arch or running the build > with QEMU_VERSION=1 (unreliable). Since transparent foreign architecture > emulation is easily present on a developer's machine and thus > influencing the build (even when done inside a chroot) it would be > useful to record whether or not foreign architecture binaries can be > executed in the buildinfo file. > > I attached a proof-of-concept patch that does exactly that. Since we > cannot rely on arch-test being installed in the build environment, this > approach cross compiles a small true.c executable for the host > architecture. This should always work because gcc is build-essential. > The binary outputs a small string instead of just relying on the exit > code to guard against QEMU_VERSION=1 "disabling" of emulation. The field > 'Can-Execute-Host-Architecture is only added when cross-compiling, i.e > when host and build architectures mismatch. > > Thanks! > > cheers, josch
>From 62179358b57d09fc8c6bb7a59deb128c67cbe522 Mon Sep 17 00:00:00 2001
From: Johannes Schauer Marin Rodrigues <jo...@mister-muffin.de>
Date: Wed, 18 May 2022 07:11:39 +0200
Subject: [PATCH] dpkg-genbuildinfo: when cross-compiling add
Can-Execute-Host-Architecture field
---
scripts/dpkg-genbuildinfo.pl | 32 +++++++++++++++++++++++++++++++-
1 file changed, 31 insertions(+), 1 deletion(-)
diff --git a/scripts/dpkg-genbuildinfo.pl b/scripts/dpkg-genbuildinfo.pl
index e05fce048..a296a7314 100755
--- a/scripts/dpkg-genbuildinfo.pl
+++ b/scripts/dpkg-genbuildinfo.pl
@@ -28,13 +28,14 @@ use warnings;
use List::Util qw(any);
use Cwd;
use File::Basename;
+use File::Temp qw(tmpnam);
use POSIX qw(:fcntl_h :locale_h strftime);
use Dpkg ();
use Dpkg::Gettext;
use Dpkg::Checksums;
use Dpkg::ErrorHandling;
-use Dpkg::Arch qw(get_build_arch get_host_arch debarch_eq);
+use Dpkg::Arch qw(get_build_arch get_host_arch debarch_eq
debarch_to_gnutriplet);
use Dpkg::Build::Types;
use Dpkg::Build::Info qw(get_build_env_allowed);
use Dpkg::BuildOptions;
@@ -46,6 +47,8 @@ use Dpkg::Control;
use Dpkg::Changelog::Parse;
use Dpkg::Deps;
use Dpkg::Dist::Files;
+use Dpkg::Exit qw(push_exit_handler);
+use Dpkg::IPC;
use Dpkg::Lock;
use Dpkg::Version;
use Dpkg::Vendor qw(get_current_vendor run_vendor_hook);
@@ -455,6 +458,33 @@ $fields->{'Installed-Build-Depends'} =
collect_installed_builddeps($control);
$fields->{'Environment'} = "\n" . cleansed_environment();
+if (get_host_arch() ne $fields->{'Build-Architecture'}) {
+ # if we are cross-compiling, record whether it was possible to execute the
+ # host architecture by cross-compiling and executing a small host-arch
+ # binary
+
+ my $tmpname = tmpnam();
+ push_exit_handler(sub { unlink($tmpname) });
+ my ($stdout, $stderr) = ('', '');
+ my $testprog = 'int main(){write(1,"ok",2);return 0;}';
+ spawn(exec => [ debarch_to_gnutriplet(get_host_arch()) . '-gcc', '-x',
'c', '-o', $tmpname, '-' ],
+ wait_child => 1, nocheck => 1,
+ to_string => \$stdout,
+ error_to_string => \$stderr,
+ from_string => \$testprog);
+ if ($?) {
+ print { *STDOUT } $stdout;
+ print { *STDERR } $stderr;
+ subprocerr("gcc -x c -");
+ }
+ spawn(exec => [ $tmpname ], error_to_file => '/dev/null', 'to_string' =>
\$stdout, wait_child => 1, nocheck => 1);
+ if ($? == 0 && $stdout eq "ok") {
+ $fields->{'Can-Execute-Host-Architecture'} = "true";
+ } else {
+ $fields->{'Can-Execute-Host-Architecture'} = "false";
+ }
+}
+
# Generate the buildinfo filename.
if ($stdout) {
# Nothing to do.
--
2.35.1
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