fix: build ooniprobe for linux using debian/amd64

In ooni/probe#1741, we observed that
every attempt to use `docker --platform` along with `debian` for
packaging ooniprobe fails with `SEGFAULT`, except when using
the `debian:oldstable` container.

To fix this issue, in this diff we fix Debian packaging to run on
any debian system (`debian:stable` in our case) provided that we
have `qemu-user-static` installed on the system and the system is
a Debian (or Debian-derived) system.

The trick here is to use `dpkg-buildpackage -a $deb_arch`. We
also need to disable a few `debian/rules` that we don't actually
need anyway.

Closes ooni/probe#1741.

.github/workflows/linux.yml

@@ -4,6 +4,8 @@ on:
   push:
     branches:
       - "release/**"
+      - "stable"
+      - "linux"
 
 jobs:
   build_386:

CLI/linux/pkgdebian

@@ -7,8 +7,9 @@
 # 1. the `ooniprobe` we are packaging is available at
 # this path `./CLI/linux/$GOARCH/ooniprobe`;
 #
-# 2. we are running on a debian system that has the same
-# architecture of the `ooniprobe` we are packaging.
+# 2. we are running on a debian system that has is capable
+# of running binaries for the architecture that we wanna
+# package, either natively or via qemu-user-static.
 
 if [ $# -ne 1 ] && [ $# -ne 2 ]; then
 	echo "usage: $0 {arch} [run_number]" 1>&2
@@ -31,9 +32,28 @@ if [ -n "$run_number" ]; then
 	version="${version}~${run_number}"
 fi
 
+darch=""
+case $goarch in
+386)
+	darch="i386"
+	;;
+amd64)
+	darch="amd64"
+	;;
+arm)
+	darch="armhf"
+	;;
+arm64)
+	darch="arm64"
+	;;
+esac
+echo "Building for GOARCH=$goarch / DEBARCH=$darch"
+
 # The OONI_DEB_DRY_RUN is a semi-undocumented feature allowing
 # us to see the commands that would be run by this script.
 
+$OONI_DEB_DRY_RUN dpkg --add-architecture $darch
+
 # install the dependencies required by the build process
 $OONI_DEB_DRY_RUN apt-get update -q
 $OONI_DEB_DRY_RUN apt-get build-dep -y --no-install-recommends .
@@ -42,7 +62,7 @@ $OONI_DEB_DRY_RUN apt-get build-dep -y --no-install-recommends .
 $OONI_DEB_DRY_RUN cp ./debian/changelog ./debian/changelog.oocopy
 
 $OONI_DEB_DRY_RUN dch -v "$version" "New version ${version}"
-$OONI_DEB_DRY_RUN dpkg-buildpackage -us -uc -b
+$OONI_DEB_DRY_RUN dpkg-buildpackage -a $darch -us -uc -b
 
 # restore the original changelog file
 $OONI_DEB_DRY_RUN mv ./debian/changelog.oocopy ./debian/changelog
@@ -51,22 +71,6 @@ $OONI_DEB_DRY_RUN mv ./debian/changelog.oocopy ./debian/changelog
 # of it when using a build container
 $OONI_DEB_DRY_RUN mv ../*.deb .
 
-darch=""
-case $goarch in
-386)
-	darch="i386"
-	;;
-amd64)
-	darch="amd64"
-	;;
-arm)
-	darch="armhf"
-	;;
-arm64)
-	darch="arm64"
-	;;
-esac
-
 # install the package on the container as a smoke test to
 # ensure that it is installable.
 DEBIAN_FRONTEND=noninteractive dpkg -i "ooniprobe-cli_${version}_${darch}.deb"

debian/rules

@@ -14,5 +14,17 @@ override_dh_auto_build:
 override_dh_dwz:
 	true
 
+override_dh_strip:
+	# We cross compile and build packages for any arch from
+	# linux/amd64 so we need to avoid this step. BTW this step
+	# is not needed because we already strip when building.
+	true
+
+override_dh_makeshlibs:
+	# We cross compile and build packages for any arch from
+	# linux/amd64 so we need to avoid this step. BTW this step
+	# is not needed because we don't have any shlib.
+	true
+
 override_dh_auto_install:
 	dh_auto_install -- --no-source

mk

@@ -278,17 +278,17 @@ GOLANG_DOCKER_IMAGE = golang:$(GOLANG_VERSION_NUMBER)-alpine
 # This extra .PHONY for linux/386 is to help printing targets 🤷.
 .PHONY:     ./CLI/linux/386/ooniprobe
 ./debian/386: search/for/docker ./CLI/linux/386/ooniprobe
-	docker pull --platform linux/386 debian:stable
-	docker run --platform linux/386 -v $(shell pwd):/ooni -w /ooni debian:stable ./CLI/linux/pkgdebian 386 "$(DEBIAN_TILDE_VERSION)"
+	docker pull debian:stable
+	docker run -v $(shell pwd):/ooni -w /ooni debian:stable ./CLI/linux/pkgdebian 386 "$(DEBIAN_TILDE_VERSION)"
 
 #help:
 #help: * `./mk ./debian/amd64`: debian/amd64
 .PHONY:   ./debian/amd64
 # This extra .PHONY for linux/amd64 is to help printing targets 🤷.
 .PHONY:     ./CLI/linux/amd64/ooniprobe
 ./debian/amd64: search/for/docker ./CLI/linux/amd64/ooniprobe
-	docker pull --platform linux/amd64 debian:stable
-	docker run --platform linux/amd64 -v $(shell pwd):/ooni -w /ooni debian:stable ./CLI/linux/pkgdebian amd64 "$(DEBIAN_TILDE_VERSION)"
+	docker pull debian:stable
+	docker run -v $(shell pwd):/ooni -w /ooni debian:stable ./CLI/linux/pkgdebian amd64 "$(DEBIAN_TILDE_VERSION)"
 
 # Note that we're building for armv7 here
 #help:
@@ -297,17 +297,17 @@ GOLANG_DOCKER_IMAGE = golang:$(GOLANG_VERSION_NUMBER)-alpine
 # This extra .PHONY for linux/arm is to help printing targets 🤷.
 .PHONY:     ./CLI/linux/arm/ooniprobe
 ./debian/arm: search/for/docker ./CLI/linux/arm/ooniprobe
-	docker pull --platform linux/arm/v7 debian:stable
-	docker run --platform linux/arm/v7 -v $(shell pwd):/ooni -w /ooni debian:stable ./CLI/linux/pkgdebian arm "$(DEBIAN_TILDE_VERSION)"
+	docker pull debian:stable
+	docker run -v $(shell pwd):/ooni -w /ooni debian:stable ./CLI/linux/pkgdebian arm "$(DEBIAN_TILDE_VERSION)"
 
 #help:
 #help: * `./mk ./debian/arm64`: debian/arm64
 .PHONY:   ./debian/arm64
 # This extra .PHONY for linux/arm64 is to help printing targets 🤷.
 .PHONY:     ./CLI/linux/arm64/ooniprobe
 ./debian/arm64: search/for/docker ./CLI/linux/arm64/ooniprobe
-	docker pull --platform linux/arm64 debian:stable
-	docker run --platform linux/arm64 -v $(shell pwd):/ooni -w /ooni debian:stable ./CLI/linux/pkgdebian arm64 "$(DEBIAN_TILDE_VERSION)"
+	docker pull debian:stable
+	docker run -v $(shell pwd):/ooni -w /ooni debian:stable ./CLI/linux/pkgdebian arm64 "$(DEBIAN_TILDE_VERSION)"
 
 #help:
 #help: The `./mk ./CLI/ooniprobe/linux` command builds the ooniprobe official command