Weird behaviour about system types

[Sébastien Hinderer]

Dear all,

I just noticed a behaviour of a configure script that surprises me.

The configure.ac script does contain the AC_CANONICAL_BUILD,
AC_CANONICAL_HOST and AC_CANONICAL_TARGET macros.

I am calling the generated configure script as follows:

  ./configure --build=x86_64-pc-linux-gnu --host=aarch64-linux-gnu

I am getting the following output:

checking build system type... x86_64-pc-linux-gnu
checking host system type... aarch64-unknown-linux-gnu
checking target system type... aarch64-unknown-linux-gnu

I am okay with the first line but to absolutely not understandthe second
and third line. Why do the host and system types contain an "unknown"
string?

Since I gave the --host=aarch64-linux-gnu arguemnt, I expected this to
be the canonical system type. And also, I thought the target system type
would default to the user-provided host system type, which does not seem
to be the case.

Should I then rely on the host_alias and target_alias variables? It
feels odd because they may not be in canonical form and also this means
that the target will have to be explicitly given, which I thought I
don't have to do.

Any help would be greatly appreciated. Thanks!

Sébastien.