[PATCH v2] Add `--with-install-sysroot=' configuration option

[Joseph Myers]

On Mon, 18 Nov 2019, Maciej W. Rozycki wrote:

> > 4. How does this interact with sysroot suffixes (again, this should be 
> > made clear in the documentation)?
> 
>  There is no interaction, the patch merely changes where the libraries are 
> installed.  If the installation sysroot directory chosen is not one known 
> by the GCC driver, then the newly-installed target libraries won't be 
> automatically used (that of course can be changed with the appropriate use 
> of the `-B', `-L' and `--sysroot=' driver options).

Perhaps the "sysroot" phrasing of the option name is confusing.

The documentation in install.texi says "@var{dir} rather than 
@option{$@{gcc_tooldir@}/lib}".  If that means, for example, that when 
"-print-multi-os-directory" prints "../lib64" the libraries are installed 
in $dir/../lib64 (so you'd pass --with-install-sysroot=/some/where/lib 
rather than --with-install-sysroot=/some/where), it's definitely not a 
sysroot.  If in fact $dir/lib/../lib64 would be used, the documentation 
should say so.

But even then, if you configure GCC using "--with-sysroot" or 
"--with-build-sysroot", both of those paths are the top-level sysroot, to 
which the sysroot suffix gets appended before GCC uses it for any purpose, 
unless you explicitly build using --no-sysroot-suffix.  So I still think 
it's natural for a user of GCC's configure scripts to expect the new 
option, like the other sysroot-related configure options, also to be one 
to which the per-multilib sysroot suffix gets appended before GCC uses it.  
And if it's not like that, the documentation needs to say so explicitly.

-- 
Joseph S. Myers
joseph@codesourcery.com