[Buildroot] [PATCH v4 2/2] Makefile: add check of binaries architecture

[Thomas Petazzoni]

As shown recently by the firejail example, it is easy to miss that a
package builds and installs binaries without actually cross-compiling
them: they are built for the host architecture instead of the target
architecture.

This commit adds a small helper script, check-bin-arch, called as a
GLOBAL_INSTRUMENTATION_HOOKS at the end of the target installation of
each package, to verify that the files installed by this package have
been built for the correct architecture.

Being called as a GLOBAL_INSTRUMENTATION_HOOKS allows the build to error
out right after the installation of the faulty package, and therefore
get autobuilder error detection properly assigned to this specific
package.

Example output with the firejail package enabled, when building for an
ARM target:

ERROR: ./usr/lib/firejail/libconnect.so (from firejail) architecture is Advanced Micro Devices X86-64, should be ARM
ERROR: ./usr/bin/firejail (from firejail) architecture is Advanced Micro Devices X86-64, should be ARM
ERROR: ./usr/lib/firejail/libtrace.so (from firejail) architecture is Advanced Micro Devices X86-64, should be ARM
ERROR: ./usr/lib/firejail/libtracelog.so (from firejail) architecture is Advanced Micro Devices X86-64, should be ARM
ERROR: ./usr/lib/firejail/ftee (from firejail) architecture is Advanced Micro Devices X86-64, should be ARM
ERROR: ./usr/lib/firejail/faudit (from firejail) architecture is Advanced Micro Devices X86-64, should be ARM
ERROR: ./usr/bin/firemon (from firejail) architecture is Advanced Micro Devices X86-64, should be ARM
ERROR: ./usr/bin/firecfg (from firejail) architecture is Advanced Micro Devices X86-64, should be ARM
package/pkg-generic.mk:306: recipe for target '/home/thomas/projets/buildroot/output/build/firejail-0.9.44.8/.stamp_target_installed' failed
make[1]: *** [/home/thomas/projets/buildroot/output/build/firejail-0.9.44.8/.stamp_target_installed] Error 1

Many thanks to Yann E. Morin and Arnout Vandecappelle for their reviews
and suggestions.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni at free-electrons.com>
---
Changes since v3:
 - Pass TARGET_READELF instead of TARGET_CROSS, suggested by Arnout
 - Pass BR2_READELF_ARCH_NAME to the script, instead of parsing the BR
   config file. Suggested by Yann.
 - Use LC_ALL=C when calling readelf, to avoid surprises. Suggested by
   Yann.
 - Reword the error message, according to Yann suggestion.

Changes since v2:
 - Moved as a per-package check, so that we detect the faulty package
   earlier, and get correct autobuilder notifications.
 - Use TARGET_DIR from the environment and use BR2_CONFIG to retrieve
   the value of BR2_READELF_ARCH_NAME.
 - Skip firmware files in /lib/firmware and /usr/lib/firmware.
 - Simply ignore files for which readelf returned an empty Machine
   field, as a way to quickly detect non-ELF files.

Changes since v1:
 - Following Yann E. Morin's comment, restrict the check to bin, lib,
   sbin, usr/bin, usr/lib and usr/sbin, in order to avoid matching
   firmware files that could use the ELF format but be targeted for
   other architectures.
---
 package/pkg-generic.mk         | 11 +++++++++++
 support/scripts/check-bin-arch | 39 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 50 insertions(+)
 create mode 100755 support/scripts/check-bin-arch

diff --git a/package/pkg-generic.mk b/package/pkg-generic.mk
index e8a8021..73e1bc2 100644
--- a/package/pkg-generic.mk
+++ b/package/pkg-generic.mk
@@ -87,6 +87,17 @@ define step_pkg_size
 endef
 GLOBAL_INSTRUMENTATION_HOOKS += step_pkg_size
 
+# Relies on step_pkg_size, so must be after
+define check_bin_arch
+	$(if $(filter end-install-target,$(1)-$(2)),\
+		support/scripts/check-bin-arch $(3) \
+			$(BUILD_DIR)/packages-file-list.txt \
+			$(TARGET_READELF) \
+			$(BR2_READELF_ARCH_NAME))
+endef
+
+GLOBAL_INSTRUMENTATION_HOOKS += check_bin_arch
+
 # This hook checks that host packages that need libraries that we build
 # have a proper DT_RPATH or DT_RUNPATH tag
 define check_host_rpath
diff --git a/support/scripts/check-bin-arch b/support/scripts/check-bin-arch
new file mode 100755
index 0000000..63d941f
--- /dev/null
+++ b/support/scripts/check-bin-arch
@@ -0,0 +1,39 @@
+#!/bin/bash
+
+PACKAGE=$1
+PACKAGE_FILE_LIST=$2
+TARGET_READELF=$3
+READELF_ARCH_NAME=$4
+
+exitcode=0
+
+PKG_FILES=$(sed -r -e "/^${PACKAGE},(.+)$/!d; s//\1/;" ${PACKAGE_FILE_LIST})
+
+for f in ${PKG_FILES} ; do
+	# Skip firmware files, they could be ELF files for other
+	# architectures
+	if [[ "${f}" =~ ^\./(usr/)?lib/firmware/.* ]]; then
+		continue
+	fi
+
+	# Get architecture using readelf
+	arch=$(LC_ALL=C ${TARGET_READELF} -h "${TARGET_DIR}/${f}" 2>&1 | \
+		       sed -r -e '/^  Machine: +(.+)/!d; s//\1/;')
+
+	# If no architecture found, assume it was not an ELF file
+	if test "${arch}" = "" ; then
+		continue
+	fi
+
+	# Architecture is correct
+	if test "${arch}" = "${READELF_ARCH_NAME}" ; then
+		continue
+	fi
+
+	printf 'ERROR: architecture for %s (from %s) is %s, should be %s\n' \
+	       "${f}" "${PACKAGE}" "${arch}" "${READELF_ARCH_NAME}"
+
+	exitcode=1
+done
+
+exit ${exitcode}
-- 
2.7.4