Re: Warnings regarding errata fixed and mapping symbol missing

[Egor Pasko <pasko at google dot com>]

Thanks, Cary.

I am looking into using aarch64-gold for Chrome, where the general
approach is to treat warnings as errors, except explicit list of
warnings for which "we know what we are doing".

On Thu, Jul 2, 2015 at 8:01 PM, Cary Coutant <ccoutant@gmail.com> wrote:
> > Now our customers are able to run arm-gold and aarch64-gold with all
> > necessary errata fixes (thanks for the review). Now the next problem
> > is that gold report warnings regarding errata being fixed and mapping
> > symbols being missing, since Android/Chrome build script treats
> > warnings as errors, the warnings are annoying. Also one justification
> > for silencing them is that bfd gives no warning for such at all.
> > (Actually we chrome land has a local patch for 2.24/2.25 that disables
> > missing mapping symbols warning.)
> >
> > I don't know if this had been discussed before, but is there an option
> > to silence these 2 warnings for gold? If not, could we add options to
> > silence these 2 warnings? What do you think?
>
> How about changing the errata-fixed warnings to info messages? I see
> no reason why they should be warnings -- you've asked the linker to
> fix errata that are fully expected.

This sounds good to me.

> For the warning about missing mapping symbols, it seems to me that the
> warning is justified -- if you ask it to scan for errata, but you
> can't, the user ought to be told about it. Why is that not something
> that should be fixed on the compiler side? If it's considered a normal
> case, and an absence of mapping symbols implies that the linker
> doesn't *need* to scan that section for errata, then just remove the
> warning. But if there's a real possibility that the section might have
> instruction sequences that need stubs, I'd want to keep the warning,
> and pressure the compiler to fix it.

In Chromium/Chrome we would prefer _not_ to use --no-fatal-warnings
when switching to ld.gold. Can something like
--no-cortex-a53-errata-XXXX-warning be introduced in gold?

As far as I understand, currently ld.bfd does not warn about missing
mapping symbols. So there is an argument for maintaining consistency
with ld.bfd.

Looking at a few examples of missed mapping symbols: I saw some of
those not being output sometimes for data sections by GAS, but I am
not confident enough to assert that this only happens for non-code
sections. Not sure what to do, this makes the process of patching for
errata look unreliable.

-- 
Egor Pasko