why is gap-install linked with libgap?

[dimpase]

In Makefile.rules one has

# build rule for the gap executable used by the `install-bin` target
build/gap-install: libgap$(SHLIB_EXT) cnf/GAP-LDFLAGS cnf/GAP-LIBS cnf/GAP-OBJS build/obj/build/main.c.o
        $(QUIET_LINK)$(LINK) $(GAP_LDFLAGS) build/obj/build/main.c.o $(GAP_LIBS) -L${abs_builddir} -lgap -o $@

endif

Does this mean that gap as installed by make install is using libgap, unlike ./gap produced by make ?

And so, in particular, packages producing GAP kernel extensions might need to be linked to libgap (we observe errors on a recent arm64 macOS to this extent).
@culler

[fingolfin]

Does this mean that gap as installed by make install is using libgap, unlike ./gap produced by make ?

Yes exactly.

And so, in particular, packages producing GAP kernel extensions might need to be linked to libgap

Yup. As a general rule, you need to link a kernel extension against the kernel it is supposed to be used with, and using the sysinfo.gap resp. gac that was built / installed with that kernel, as only that is guaranteed (well, up to mistakes on our part of course) to have the correct compiler and linker flags.

[dimpase]

I am not sure I understand what "link a kernel extension against the kernel" means. As I try the current master branch on arm64 macOS, with cd bar && ./configure --prefix=foo && make && make install, I then configure/build, say, crypting package with

./configure foo/lib/gap # sysroot.gap is there
make && make install

Then I fake installing the packages by

ln -s bar/pkg foo/share/gap/

and foo/bin/gap runs and successfully loads crypting (and runs its tests).
However, crypting.so isn't linked to anything except a system library, i.e.

% otool -L bin/aarch64-apple-darwin24-default64-kv10/crypting.so 
bin/aarch64-apple-darwin24-default64-kv10/crypting.so:
        /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1351.0.0)
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