bug#71174: libb2 fails to build during cross-compilation

[Christoph Buck]

Hi!

The package libb2 in `(gnu packages crypto)` fails during
cross-compilation from `x86_64-linux-gn` to `aarch64-linux-gnu`, but
possible more combinations are broken.

Steps to reproduce:

> git log --oneline HEAD^..HEAD

> 9901416233 (origin/master, origin/HEAD) gnu: ctl: Update to 1.5.3.

> ./pre-inst-env guix build libb2 --system=x86_64-linux > 
> --target=aarch64-linux-gnu --no-substitutes --no-grafts

> [...]
> checking for objdir... .libs
> checking if aarch64-linux-gnu-gcc supports -fno-rtti -fno-exceptions... no
> checking for aarch64-linux-gnu-gcc option to produce PIC... -fPIC -DPIC
> checking if aarch64-linux-gnu-gcc PIC flag -fPIC -DPIC works... yes
> checking if aarch64-linux-gnu-gcc static flag -static works... yes
> checking if aarch64-linux-gnu-gcc supports -c -o file.o... yes
> checking if aarch64-linux-gnu-gcc supports -c -o file.o... (cached) yes
> checking whether the aarch64-linux-gnu-gcc linker 
> (/gnu/store/kh7kl57h5i3vzx9hbbairnkkgnx7kf61-gcc-cross-aarch64-linux-gnu-11.3.0/libexec/gcc/aarch64-linux-gnu/ld)
>  supports shared libraries... yes
> checking whether -lc should be explicitly linked in... no
> checking dynamic linker characteristics... GNU/Linux ld.so
> checking how to hardcode library paths into programs... immediate
> checking whether stripping libraries is possible... yes
> checking if libtool supports shared libraries... yes
> checking whether to build shared libraries... yes
> checking whether to build static libraries... yes
> checking whether C compiler accepts -O3... yes
> checking whether C compiler accepts -msse2... no
> configure: error: Compiler does not know -msse2.
> error: in phase 'configure': uncaught exception:
> %exception #<&invoke-error program: 
> "/gnu/store/rib9g2ig1xf3kclyl076w28parmncg4k-bash-minimal-5.1.16/bin/bash" 
> arguments: ("./configure" "CC_FOR_BUILD=gcc" 
> "CONFIG_SHELL=/gnu/store/rib9g2ig1xf3kclyl076w28parmncg4k-bash-minimal-5.1.16/bin/bash"
>  
> "SHELL=/gnu/store/rib9g2ig1xf3kclyl076w28parmncg4k-bash-minimal-5.1.16/bin/bash"
>  "--prefix=/gnu/store/5cy4lw70ilgwbrmav12xli0lyqzwvmk5-libb2-0.98.1" 
> "--enable-fast-install" "--build=x86_64-unknown-linux-gnu" 
> "--host=aarch64-linux-gnu" "--enable-fat" "--disable-native") exit-status: 1 
> term-signal: #f stop-signal: #f>
> phase `configure' failed after 1.2 seconds
> command 
> "/gnu/store/rib9g2ig1xf3kclyl076w28parmncg4k-bash-minimal-5.1.16/bin/bash" 
> "./configure" "CC_FOR_BUILD=gcc" 
> "CONFIG_SHELL=/gnu/store/rib9g2ig1xf3kclyl076w28parmncg4k-bash-minimal-5.1.16/bin/bash"
>  
> "SHELL=/gnu/store/rib9g2ig1xf3kclyl076w28parmncg4k-bash-minimal-5.1.16/bin/bash"
>  "--prefix=/gnu/store/5cy4lw70ilgwbrmav12xli0lyqzwvmk5-libb2-0.98.1" 
> "--enable-fast-install" "--build=x86_64-unknown-linux-gnu" 
> "--host=aarch64-linux-gnu" "--enable-fat" "--disable-native" failed with 
> status 1
> builder for `/gnu/store/rlhm80fld1h2xszn3yh7x5fvr295x6qh-libb2-0.98.1.drv' 
> failed with exit code 1
> build of /gnu/store/rlhm80fld1h2xszn3yh7x5fvr295x6qh-libb2-0.98.1.drv failed
> Could not find build log for 
> '/gnu/store/rlhm80fld1h2xszn3yh7x5fvr295x6qh-libb2-0.98.1.drv'.
> guix build: error: build of > 
> `/gnu/store/rlhm80fld1h2xszn3yh7x5fvr295x6qh-libb2-0.98.1.drv' failed


Root-cause:

The `configure-flags` in the package definition of libb2 are broken for
cross-compilation.

> `(#:configure-flags
>        (list
>         ,@(if (any (cute string-prefix? <> (or (%current-system)
>                                                (%current-target-system)))
>                    '("x86_64" "i686"))
>               ;; fat only checks for Intel optimisations
>               '("--enable-fat")
>               '())
>         "--disable-native"))

Shot-circuit evaluation of the `or` operator leads to enabling of `fat`
as long as `%current-system` is set to `x86_64/i686` regardless of the
value of `%current-target-system`. If `%current-target-system` is set
for example to the `aarch64-linux-gnu` triplet, `--enable-fat` is added
to the configure flags which in turn will break compilation. I am not
entirley sure, what `enable-fat` does. From my understanding this flag
enables fat binaries (or multiarchitecture binaries), which seems to
require the `sse2` instruction set. The cross compile toolchain for
aarch64-linux-gnu (and mostlikey other toolchains as well) does not
support this instruction set.

As a quick workaround, i came up with the following patch:

> `(#:configure-flags
>        (list
>         ,@(let ((check-x86 (lambda (triplet) (any (cute string-prefix? <> 
> triplet) '("x86_64" "i868")))))
>             (if (%current-target-system)
>                 (if (check-x86 (%current-target-system))
>                     '("--enable-fat")
>                     '())
>                 (if (check-x86 (%current-system))
>                     '("--enable-fat")
>                     '())))
>         "--disable-native"))

This enables fat binaries if the target system is set to `x86_64/i868`
regardless of the value of `%current-system`. If the target system is
not set, fat binaries are only enabled if the `%current-system` is set
to `x86_64/i868`. Most likely there is a cleaner way to write this, but
i am a total scheme newbee. If required, i can submit a real patch.

Best regards

Christoph