Re: [PATCH] Add .gnu.lto_.meta section.

[Richard Biener <richard.guenther@gmail.com>]

On Fri, Jun 21, 2019 at 4:01 PM Martin Liška <mliska@suse.cz> wrote:
>
> On 6/21/19 2:57 PM, Jan Hubicka wrote:
> > This looks like good step (and please stream it in host independent
> > way). I suppose all these issues can be done one-by-one.
>
> So there's a working patch for that. However one will see following errors
> when using an older compiler or older LTO bytecode:
>
> $ gcc main9.o -flto
> lto1: fatal error: bytecode stream in file ‘main9.o’ generated with LTO version -25480.4493 instead of the expected 9.0
>
> $ gcc main.o
> lto1: internal compiler error: compressed stream: data error

This is because of your change to bitfields or because with the old
scheme the header with the
version is compressed (is it?).  I'd simply avoid any layout changes
in the version check range.

> To be honest, I would prefer the new .gnu.lto_.meta section.
> Richi why is that so ugly?

Because it's a change in the wrong direction and doesn't solve the
issue we already
have (cannot determine if a section is compressed or not).  ELF section overhead
is quite big if you have lots of small functions.

Richard.

>
> Martin