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Date:      Sat, 15 Apr 2017 09:30:49 +1000 (AEST)
From:      Gerald Pfeifer <gerald@pfeifer.com>
To:        Pedro Giffuni <pfg@FreeBSD.org>, freebsd.contact@marino.st
Cc:        Mark Millard <markmi@dsl-only.net>, freebsd-ports@freebsd.org,  freebsd-toolchain@freebsd.org, freebsd-arm@freebsd.org,  freebsd-head@freebsd.org, ericturgeon.bsd@gmail.com
Subject:   Re: lang/gcc6-aux for head beyond __nonnull related issues: vm_ooffset_t and vm_pindex_t related changes (and more)
Message-ID:  <alpine.LNX.2.21.1704150928320.4604@anthias.pfeifer.com>
In-Reply-To: <E86AC2D1-EE2D-4E33-85FD-8069B050421F@FreeBSD.org>
References:  <E54E495A-E4C8-40B3-B1E8-133A9872B6B2@dsl-only.net> <9758023E-1526-41F9-9416-6AC8AD3201B5@dsl-only.net> <E86AC2D1-EE2D-4E33-85FD-8069B050421F@FreeBSD.org>

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On Thu, 13 Apr 2017, Pedro Giffuni wrote:
> I didn’t want to get into this but the problem is that as part of it's
> build/bootstrapping process, GCC historically takes system headers
> and attempts to “fix” them. I am unsure the fixes do anything at all
> nowadays but the effect is that the compiler tends to take snapshots
> of the system headers when it is built. cdefs.h is used by all the
> system headers so changes in cdefs.h have good chances affecting
> such builds but any change are likely to cause similar trouble.
> 
> In the case of gcc-aux, it appears the compilation is based on a
> bootstrap compiler which already carries outdated headers.
> A workaround, suggested by gerald@ the last time a similar issue
> happened was to run for install-tools/fixinc.sh. I think that may
> regenerate the headers and let the build use updated headers.
> Ultimately gcc-aux needs maintainer intervention and using
> outdated headers will break sooner or later: especially on -current.

Indeed, thanks for the analysis/background, Pedro!

I had a look at gcc6-aux is based on the 20170202 snapshot of GCC 6, 
and perhaps John (as the maintainer of that port) has plans to update 
it?  Let me copy him.

Gerald

PS: John, if you have an update, happy to help and apply that for you.
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Subject: Re: WITH_LLD_IS_LD vs default WITHOUT_SYSTEM_COMPILER: What are the
 reasons?
From: Mark Millard <markmi@dsl-only.net>
In-Reply-To: <7DB9F23E-2D55-44C3-AA91-C209BF584C4A@andric.com>
Date: Fri, 14 Apr 2017 17:16:14 -0700
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To: Dimitry Andric <dimitry@andric.com>
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On 2017-Apr-14, at 2:35 PM, Dimitry Andric <dimitry at andric.com> wrote:

> On 14 Apr 2017, at 22:40, Mark Millard <markmi at dsl-only.net> wrote:
>> 
>> man src.conf (from -r315914 ) reports:
>> 
>>    WITH_LLD_IS_LD
>>            Set to use LLVM's LLD as the system linker, instead of GNU
>>            binutils ld.
>> 
>>            This is a default setting on arm64/aarch64.  When set, these
>>            options are also in effect:
>> 
>>            WITHOUT_SYSTEM_COMPILER (unless WITH_SYSTEM_COMPILER is set
>>            explicitly)
>> 
>> I'm curious about:
>> 
>> A) Why there is a bias to avoid the system compiler?
> 
> These are just the defaults, detected by the script that generates
> src.conf.5.  The setting of MK_SYSTEM_COMPILER is actually dependent on
> the host, so it's technically incorrect to have src.conf.5 mention that
> it is off by default.

Ahh. I took the mention of WITH_LLD_IS_LD and WITHOUT_SYSTEM_COMPILER
as it was written as something that was being specially enforced, implying
some form of lack of full independence. I wondered about what contexts
trying WITH_SYSTEM_COMPILER might be broken when WITH_LLD_IS_LD was also
in use.

>> and by contrast:
>> 
>> B) What sort of context justifies explicitly setting
>>  WITH_SYSTEM_COMPILER when WITH_LLD_IS_LD is in use?
> 
> The settings are mostly orthogonal.  MK_SYSTEM_COMPILER was created to
> avoid building a bootstrap compiler, if the system (host) compiler is
> new enough.

I'm familiar with the WITH_SYSTEM_COMPILER vintage material have
have been using it and other such things right along.

My worry for my knowledge-base would be the "mostly" part of
"mostly orthogonal": When is there a lack of independence?
(Presuming system-clang 4.0 instead of system-gcc 4.2.1.)

> At some point you could also image a MK_SYSTEM_LINKER setting, which
> would avoid building the bootstrap linker, if the system linker is new
> enough.

Yep.

So it sounds like I can freely mix WITH_LLD_IS_LD and WITH_SYSTEM_COMPILER
in any system-clang 4.0 based system build context, no actual problem
cases, even if the existing system build used a binutils ld (for example).

Thanks for the information.

===
Mark Millard
markmi at dsl-only.net




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