Cross-compiled GCC 6.1.0 has "../lib" instead of "/usr/lib" in -print-search-dirs output

[Matthew Fortune]

Alastair Hughes <hobbitalastair@gmail.com> writes:
> I've cross compiled GCC 6.1.0 (target/build is mips, host is x86_64).

This description does not match the log. The log is for: build=x86_64
host/target=mips. The log shows the build system using a pre-installed
x86_64->mips cross compiler when building libgcc/libstdc++.

> The resulting compiler will not run as it cannot find cc1, because the
> search dirs are incorrect; they are prefixed with "../lib" instead of
> "/usr/lib" (eg instead of /usr/lib/gcc/mips-linux-musl/6.1.0/ ..., the
> path is ../lib/gcc/mips-linux-musl/6.1.0/ ...).

Can you show the full search paths that GCC tries?

> This issue appears to have been introduced by a change somewhere between
> GCC 5 and GCC 6, as I used to have a working build with GCC 5.
> Unfortunately, I neglected to test more recent builds...

I'm not aware of anything changing in this area but could have missed
something.

> I may well have configured something wrong. I've attached the build log
> and the PKGBUILD, which contains the configure command used.
> Hopefully someone can spot my mistake :)
> 
> If the problem is not a configuration mistake, where would I look to
> find out what could be the issue? Where does the GCC build process
> determine/set what the search dirs should be?

The search paths are constructed out of the prefix in this case as well
as having a relative path as a fallback.

The absolute path that you build GCC with (--prefix) will be searched
first with lib/gcc/xyz suffixed otherwise the directory containing the
GCC executable will be searched by suffixing ../ to get to the root of
the toolchain and then lib/gcc/xyz.

The latter form of searching only works if you invoke the 'main' GCC
executable in <root>/bin/[mips-linux-musl-]gcc if you invoke the copy
at <root>/mips-linux-musl/bin/gcc then the relative path will fail as
that copy of gcc is 2 levels deep not 1 level.

Hope that helps a bit,
Matthew