Building gcc 12 cross-compiler with --enable-lto on FreeBSD fails

Building gcc 12 cross-compiler with --enable-lto on FreeBSD fails

[Chris Johns]

Hi,

I am trying to build a cross-compiler on FreeBSD with --enable-lto because a
chip vendor is using it when building controller software that is part of a system.

The build I am using symlinks gmp, mpfr etc as source so they are built as part
of the gcc build.

The mpfr package is reporting ...

build/mpfr/config.log:configure:17408: error: Link Time Optimisation is not
supported (see config.log for details).

Should the enable option be passed to these packages?

I have assumed the enable option for LTO is for the cross compiler and not the
host gcc?

Thanks
Chris

Re: Building gcc 12 cross-compiler with --enable-lto on FreeBSD fails

[Richard Biener]

On Wed, Jun 15, 2022 at 11:27 AM Chris Johns <chris@contemporary.net.au> wrote:
>
> Hi,
>
> I am trying to build a cross-compiler on FreeBSD with --enable-lto because a
> chip vendor is using it when building controller software that is part of a system.
>
> The build I am using symlinks gmp, mpfr etc as source so they are built as part
> of the gcc build.
>
> The mpfr package is reporting ...
>
> build/mpfr/config.log:configure:17408: error: Link Time Optimisation is not
> supported (see config.log for details).
>
> Should the enable option be passed to these packages?

You shouldn't need --enable-lto, it's effect (adding lto to the set of compiled
languages) is already the default.  You can use --enable-languages=default,lto
to achieve the same effect without getting the mpfr side-effect.

> I have assumed the enable option for LTO is for the cross compiler and not the
> host gcc?

it's for the built GCC, enabling LTO support (but not for enabling
building GCC itself
with LTO).

Richard.

>
> Thanks
> Chris

Re: Building gcc 12 cross-compiler with --enable-lto on FreeBSD fails

[Chris Johns]

On 15/6/22 7:56 pm, Richard Biener wrote:
> On Wed, Jun 15, 2022 at 11:27 AM Chris Johns <chris@contemporary.net.au> wrote:
>>
>> Hi,
>>
>> I am trying to build a cross-compiler on FreeBSD with --enable-lto because a
>> chip vendor is using it when building controller software that is part of a system.
>>
>> The build I am using symlinks gmp, mpfr etc as source so they are built as part
>> of the gcc build.
>>
>> The mpfr package is reporting ...
>>
>> build/mpfr/config.log:configure:17408: error: Link Time Optimisation is not
>> supported (see config.log for details).
>>
>> Should the enable option be passed to these packages?
> 
> You shouldn't need --enable-lto, it's effect (adding lto to the set of compiled
> languages) is already the default.  You can use --enable-languages=default,lto
> to achieve the same effect without getting the mpfr side-effect.

Oh that is great and I had no idea this is how it is controlled. I have rebuilt
my compiler and it is now building. Nice.

>> I have assumed the enable option for LTO is for the cross compiler and not the
>> host gcc?
> 
> it's for the built GCC, enabling LTO support (but not for enabling
> building GCC itself
> with LTO).

It now makes sense. I will also update the RTEMS tools builds.

Thanks
Chris