Using __gnu_lto_slim to detect -fno-fat-lto-objects

[Richard Biener]

On Wed, Feb 22, 2023 at 9:19 AM Florian Weimer via Gcc <gcc@gcc.gnu.org> wrote:
>
> Can we use the COMMON symbol __gnu_lto_slim to detect
> -fno-fat-lto-objects on contemporary GNU/Linux (with the LTO linker
> plugin)?

Yes.

> We currently build the distribution with -ffat-lto-objects, and I want
> to switch away from that.  Packages will need to opt in to
> -ffat-lto-objects if static objects they build escape the buildroot.
> And to make sure that this opt-in happens, I want to fail the build if
> there would be any -fno-fat-lto-objects objects leaking.

For SUSE we're checking that no LTO bytecode leaks instead, thus we check
for __gnu_lto_v? (I think).  The reason is that even for static libraries
we do not want to ship LTO bytecode.

Richard.

> Thanks,
> Florian
>