[Buildroot] [PATCH v3] package/ncftp: fix cross compilation detection

[Yegor Yefremov via buildroot <buildroot@buildroot.org>]

From: Yegor Yefremov <yegorslists@googlemail.com>

ncftp still ships a configure script generated with autoconf 2.13, which
determines whether it is cross compiling by simply trying to run a
trivial program built with $CC, instead of looking at --host/--build.
That heuristic breaks when the build machine is able to execute the
binaries produced by the cross compiler, which is typically the case
when building for x86/x86-64 on an x86-64 machine:

  checking whether the C compiler (...) is a cross-compiler... no

configure then takes the AC_TRY_RUN path for the remaining tests. Those
tests link against the target libraries but are executed on the build
machine, so they fail as soon as more than the bare C library is
involved. The most visible victim is the curses detection, which links
the test program against the target libncurses and then runs it:

  checking for curses library headers... checking for ncurses.h... yes
  checking for curses.h... yes
  checking for curses library... no

With no curses library, ncftpbookmarks is silently dropped from the
build and installation later fails with:

  install: cannot stat '.../build/ncftp-3.3.0/bin/ncftpbookmarks': No such file or directory

Other checks are mis-detected the same way, e.g. the 64-bit integral
type checks, which end up breaking the build itself:

  checking how to scan a 64-bit integral type... cannot scan
  io_get.c:763:96: error: expected ')' before 'PRINTF_LONG_LONG'

So add a patch making the generated configure script follow what
autoconf has been doing since 2.50, and consider the build cross
compilation as soon as --host is given and differs from --build,
regardless of whether the produced binaries happen to be runnable.

Regenerating configure instead is not an option: the macros in
autoconf_local/aclocal.m4 rely on autoconf 2.13 internals (AC_LANG used
as a value, AC_FD_CC, __oline__, ...) and upstream generates configure
with a patched autoconf 2.13 (see autoconf_local/acgeneral-2.13.m4.patch
and acspecific-2.13.m4.patch). A modern autoconf fails with:

  configure.in:53: error: AC_LANG: unknown language:

This regression was introduced by commit
f8bc27111531e9607f79121414f61c0c2d5f83c0 ("package/ncftp: bump to
version 3.2.9"). Before it, a pre-configure hook regenerated configure
with autoconf precisely because the bundled script "doesn't detect
cross-compilation correctly". With 3.2.9 that regeneration started to
fail, so the hook was dropped, which brought the broken detection back.
That commit left the host-autoconf dependency behind though, so drop it
now.

The issue is present since 2025.05, and in 2025.02.x since 2025.02.1,
where the 3.2.9 bump was backported as commit
6b0e4d82c31ee04e8a6abb48323252a7cd97c177.

Fixes:
https://autobuild.buildroot.org/results/ab25f98d7ab8b397e2aa4f87af9cf1d814f3d6cc/

Assisted-by: Claude:claude-opus-5-5
Signed-off-by: Yegor Yefremov <yegorslists@googlemail.com>
---
Changes v2 -> v3:
  - identify the commit that introduced the regression and the affected
    releases, including 2025.02.x (Thomas)

Changes v1 -> v2:
  - explain why configure is patched rather than regenerated (Thomas)
  - drop the leftover host-autoconf dependency

 ...cross-compilation-from-host-and-buil.patch | 60 +++++++++++++++++++
 package/ncftp/ncftp.mk                        |  1 -
 2 files changed, 60 insertions(+), 1 deletion(-)
 create mode 100644 package/ncftp/0001-configure-detect-cross-compilation-from-host-and-buil.patch

diff --git a/package/ncftp/0001-configure-detect-cross-compilation-from-host-and-buil.patch b/package/ncftp/0001-configure-detect-cross-compilation-from-host-and-buil.patch
new file mode 100644
index 0000000000..c3ecd61d1f
--- /dev/null
+++ b/package/ncftp/0001-configure-detect-cross-compilation-from-host-and-buil.patch
@@ -0,0 +1,60 @@
+From: Yegor Yefremov <yegorslists@googlemail.com>
+Date: Thu, 3 Sep 2026 10:00:00 +0200
+Subject: [PATCH] configure: detect cross compilation from --host and --build
+
+ncftp still ships a configure script generated with autoconf 2.13, which
+determines whether it is cross compiling by simply trying to run a
+trivial program built with $CC. That heuristic breaks when the build
+machine is able to execute the binaries produced by the cross compiler,
+which is typically the case when building for x86/x86-64 on an x86-64
+machine: configure then concludes it is not cross compiling and starts
+using AC_TRY_RUN based tests.
+
+Those tests link against the target libraries but are executed on the
+build machine, so they fail as soon as more than the bare C library is
+involved. The most visible victim is the curses detection, which links
+the test program against the target libncurses and then runs it:
+
+  checking for curses library headers... checking for ncurses.h... yes
+  checking for curses.h... yes
+  checking for curses library... no
+
+With no curses library, ncftpbookmarks is silently dropped from the
+build and installation later fails with:
+
+  install: cannot stat '.../build/ncftp-3.3.0/bin/ncftpbookmarks': No such file or directory
+
+Follow what autoconf has been doing since 2.50 and consider the build
+cross compilation as soon as --host is given and differs from --build,
+regardless of whether the produced binaries happen to be runnable.
+
+Note: configure is not regenerated during the build, hence the generated
+script is patched directly.
+
+Upstream: N/A, patching a generated file (upstream has neither a public
+VCS nor a bug tracker)
+
+Signed-off-by: Yegor Yefremov <yegorslists@googlemail.com>
+---
+ configure | 7 ++++++-
+ 1 file changed, 6 insertions(+), 1 deletion(-)
+
+diff --git a/configure b/configure
+index d955e20..2311c73 100755
+--- a/configure
++++ b/configure
+@@ -845,8 +845,13 @@ int main(void){return(0);}
+ EOF
+ if { (eval echo configure:847: \"$ac_link\") 1>&5; (eval $ac_link) 2>&5; } && test -s conftest${ac_exeext}; then
+   ac_cv_prog_cc_works=yes
++  # If --host was given and differs from --build, we are cross compiling,
++  # even when the build machine happens to be able to run the binaries
++  # produced by the cross compiler.
++  if test "$host" != NONE && test "$host" != "$build"; then
++    ac_cv_prog_cc_cross=yes
+   # If we can't run a trivial program, we are probably using a cross compiler.
+-  if (./conftest; exit) 2>/dev/null; then
++  elif (./conftest; exit) 2>/dev/null; then
+     ac_cv_prog_cc_cross=no
+   else
+     ac_cv_prog_cc_cross=yes
diff --git a/package/ncftp/ncftp.mk b/package/ncftp/ncftp.mk
index c56fc86848..4075449c53 100644
--- a/package/ncftp/ncftp.mk
+++ b/package/ncftp/ncftp.mk
@@ -11,7 +11,6 @@ NCFTP_TARGET_BINS = ncftp
 NCFTP_LICENSE = ClArtistic
 NCFTP_LICENSE_FILES = doc/LICENSE.txt
 
-NCFTP_DEPENDENCIES = host-autoconf
 NCFTP_CONF_OPTS = --disable-ccdv
 
 ifeq ($(BR2_PACKAGE_NCFTP_GET),y)
-- 
2.34.1

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