Bug#1121629: libhdf4 FTCBFS: multiple reasons

[Helmut Grohne]

Source: libhdf4
Version: 4.3.1-2
Tags: patch
User: debian-cross at lists.debian.org
Usertags: ftcbfs

libhdf4 fails to cross build from source for multiple reasons. When not
building for armhf, the failure is selecting a build architecture
compiler. This is due to the upstream build system using its own
compiler detection rather than relying on the one provided by autoconf.
I am aware that you mentioned switching to CMake, but it seems like
exporting suitable CC+CXX would still be a worthwhile change in the mean
time. You can drop that once switching to CMake.

When it comes to armhf, the use of gcc-14 is implemented in a way
breaking cross builds. Toolchain build dependencies should be annotated
with -for-build or -for-host (depending on what is appropriate). The
conditional in debian/rules branches on the build architecture when it
should be branching on the host architecture and the assigned compilers
fail to account for the triplet. All of these changes apply beyond the
switch to CMake.

Once fixing these, the next build failure arises from running the built
ncgen. I am not familiar with this tool, but it ends up getting
installed into hdf4-tools, which is marked as Multi-Arch: foreign. This
suggests that we should likely be using the installed version for cross
builds only. Do you concur here?

In any case, I think we should defer the surgery about ncgen until after
the migration to CMake has proceeded. This bug report is not meant to
cover the ncgen aspect.

Helmut
-------------- next part --------------
diff -Nru libhdf4-4.3.1/debian/changelog libhdf4-4.3.1/debian/changelog
--- libhdf4-4.3.1/debian/changelog	2025-11-28 10:31:02.000000000 +0100
+++ libhdf4-4.3.1/debian/changelog	2025-11-29 13:05:43.000000000 +0100
@@ -1,3 +1,13 @@
+libhdf4 (4.3.1-2.1) UNRELEASED; urgency=medium
+
+  * Non-maintainer upload.
+  * Improve cross building. (Closes: #-1)
+    + Build depend on -for-host variants of the toolchain.
+    + Fix build vs host confusion.
+    + Always export CC and CXX as the upstream build system wrongly guesses it.
+
+ -- Helmut Grohne <helmut at subdivi.de>  Sat, 29 Nov 2025 13:05:43 +0100
+
 libhdf4 (4.3.1-2) unstable; urgency=medium
 
   * Team upload.
diff -Nru libhdf4-4.3.1/debian/control libhdf4-4.3.1/debian/control
--- libhdf4-4.3.1/debian/control	2025-11-28 10:30:24.000000000 +0100
+++ libhdf4-4.3.1/debian/control	2025-11-29 13:01:26.000000000 +0100
@@ -8,8 +8,8 @@
                chrpath,
                debhelper-compat (= 13),
                flex,
-               gcc-14 [armhf],
-               g++-14 [armhf],
+               gcc-14-for-host [armhf],
+               g++-14-for-host [armhf],
                libaec-dev,
                libjpeg-dev,
                libtirpc-dev,
diff -Nru libhdf4-4.3.1/debian/rules libhdf4-4.3.1/debian/rules
--- libhdf4-4.3.1/debian/rules	2025-11-28 10:30:12.000000000 +0100
+++ libhdf4-4.3.1/debian/rules	2025-11-29 13:05:30.000000000 +0100
@@ -13,16 +13,19 @@
 
 UPSTREAM_VERSION = $(shell echo $(DEB_VERSION_UPSTREAM) | sed -e 's/\+.*//')
 
-DEB_BUILD_ARCH ?= $(shell dpkg-architecture -qDEB_BUILD_ARCH)
-
 export DEB_CPPFLAGS_MAINT_APPEND = -I/usr/include/tirpc/
 export DEB_LDFLAGS_MAINT_APPEND = -ltirpc
 
-ifneq (,$(filter $(DEB_BUILD_ARCH),armhf))
-export CC=gcc-14
-export CXX=g++-14
+ifneq (,$(filter $(DEB_HOST_ARCH),armhf))
+CC=$(DEB_HOST_GNU_TYPE)-gcc-14
+CXX=$(DEB_HOST_GNU_TYPE)-g++-14
 endif
 
+# The upstream buildsystem defaults to CC=gcc in cross builds.
+include /usr/share/dpkg/buildtools.mk
+export CC
+export CXX
+
 ifneq (,$(findstring verbose,$(DEB_BUILD_OPTIONS)))
    DH_VERBOSE=1
    export DH_VERBOSE