Hi,

cross-building the native compiler (build_type = cross-build-native)
fails due to (1) an issue with m2, and (2) nvptx being confused about
the host/target system. The first problem is apparently old and known,
as shown by the various logs at https://crossqa.debian.net/src/gcc-13

The nvptx issue perhaps is not.

On a x86 machine, I've tried building gcc-13 with:

 DEB_BUILD_OPTIONS='nolang=m2 nocheck' sbuild --host=arm64

After a while the build failed with:

  checking build system type... x86_64-pc-linux-gnu
  checking host system type... x86_64-pc-linux-gnu
  checking target system type... nvptx-unknown-none
  [...]
  checking whether we are cross compiling... configure: error: in `/<<PKGBUILDDIR>>/build-nvptx':
  configure: error: cannot run C compiled programs.

My understanding is that both the host and target system type should be
aarch64-unknown-linux-gnu instead.

With nvptx disabled, ie with the following patch applied, and
DEB_BUILD_OPTIONS='nolang=m2', gcc-13 cross-builds successfully.
--- /tmp/gcc-13-13.2.0/debian/rules.defs	2023-12-14 19:55:12.000000000 +0100
+++ debian/rules.defs	2024-01-05 17:26:13.528700625 +0100
@@ -781,7 +781,7 @@
   offload_targets :=
   with_offload_nvptx :=
 endif
-ifneq (,$(findstring build-cross, $(build_type)))
+ifneq ($(build_type),build-native)
   offload_targets :=
   with_offload_nvptx := disabled for cross builds
 endif

 > My understanding is that both the host and target system type
 > should be aarch64-unknown-linux-gnu instead.

no, the target is always nvptx-unknown-none.

and the package should be part of a cross build, you want to have the
same set of packages.

 > My understanding is that both the host and target system type
 > should be aarch64-unknown-linux-gnu instead.

no, the target is always nvptx-unknown-none.

and the package should be part of a cross build, you want to have the
same set of packages.

Control: retitle -1 gcc-13 FTCBFS: nvptx does not cross compile
host? I tried cross building gcc 13.2.0-23 on a x86 system with:

 DEB_BUILD_OPTIONS='nolang=m2' sbuild --host=arm64

And I got the following error in build-nvptx/config.log:

 configure:4591: checking whether we are cross compiling
 configure:4599: aarch64-linux-gnu-gcc-13 -o conftest    conftest.c  >&5
 configure:4603: $? = 0
 configure:4610: ./conftest
 ../src-nvptx/configure: line 4612: ./conftest: cannot execute binary file: Exec format error

Things looked slightly better adding --build and --host to
CONFARGS_NVPTX, at least the build process went past the "checking
whether we are cross compiling" step.

diff -Nru gcc-13-13.2.0/debian/rules2 gcc-13-13.2.0/debian/rules2
--- gcc-13-13.2.0/debian/rules2	2024-03-23 13:29:34.000000000 +0100
+++ gcc-13-13.2.0/debian/rules2	2024-04-30 10:28:00.000000000 +0200
@@ -1524,7 +1524,9 @@
 	--enable-languages=c,c++,fortran,lto \
 	--enable-checking=release \
 	--with-system-zlib \
-	--without-isl
+	--without-isl \
+	--build=$(DEB_BUILD_GNU_TYPE) \
+	--host=$(DEB_HOST_GNU_TYPE)

 #	--with-build-time-tools=/$(PF)/nvptx-none/bin

However, there is still a failure later on when the nvptx Makefile tries
to run nvptx-none-gcc -dumpspecs.

GCC_FOR_TARGET is set to nvptx-none-gcc in ./build-nvptx/Makefile and
used in ./build-nvptx/gcc/Makefile, but there is no such command.

  cp xgcc gcc-cross
  nvptx-none-gcc  -dumpspecs > tmp-specs
  rm -f gfortran-cross
  /bin/bash: line 1: nvptx-none-gcc: command not found
  make[4]: *** [Makefile:2226: specs] Error 127
  make[4]: *** Waiting for unfinished jobs....
  cp gfortran gfortran-cross
  rm gcc.pod gfortran.pod lto-dump.pod
  make[4]: Leaving directory '/<<PKGBUILDDIR>>/build-nvptx/gcc'
  make[3]: *** [Makefile:4622: all-gcc] Error 2
  make[3]: Leaving directory '/<<PKGBUILDDIR>>/build-nvptx'
  make[2]: *** [Makefile:1022: all] Error 2
  make[2]: Leaving directory '/<<PKGBUILDDIR>>/build-nvptx'

Any ideas welcome. Full build log at:
https://people.debian.org/~ema/gcc-13_13.2.0-23.1_arm64.build