linux-kernel - Re: RFC: drop support for gcc

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Message-ID: <20070821195433.GE30705@stusta.de>
Date:	Tue, 21 Aug 2007 21:54:33 +0200
From:	Adrian Bunk <bunk@...nel.org>
To:	Andi Kleen <ak@...e.de>
Cc:	Randy Dunlap <randy.dunlap@...cle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jarek Poplawski <jarkao2@...pl>, linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org
Subject: Re: RFC: drop support for gcc < 4.0

On Tue, Aug 21, 2007 at 09:19:59PM +0200, Andi Kleen wrote:
> On Tue, Aug 21, 2007 at 07:35:50PM +0200, Adrian Bunk wrote:
> > Obviously a gcc <= 3.4 [1], and therefore no unit-at-a-time.
> 
> Actually there are widely used 3.3 variants that support unit-at-a-time
> (e.g. 3.3-hammer which was shipped by several distributions for some time)
> 
> There are still a lot of systems around which use gcc 3.3 (less so with
> 3.4). Unless there's a major bug that is hard to work around I would
> prefer to keep it supported.
> 
> Bogus warnings should be relatively harmless.

How many kernel developers use such old gcc versions?

And how many people notice the valid modpost warnings that can indicate
a runtime Oops?

> > And it's becoming a real maintainance problem that not only this problem 
> > but also other problems like some section mismatches [2] are only 
> > present without unit-at-a-time.
> 
> The unit-at-a-time output order is not defined, so even if it works
> with the current compiler a compiler change might still trigger
> that problem. So it would be better to fix those anyways.

The example [2] from my email is guaranteed to not be a problem with 
unit-at-a-time (as long as unit-at-a-time implies 
inline-functions-called-once - and that's although theoretically 
possible quite unlikely to change in practice).

This example is for a bug that should be fixed, but my point is the
maintainability, IOW: issues with older compilers might not be 
discovered and fixed before they go into a stable kernel.

We currently support 6 different stable gcc release series plus heavily 
modified vendor branches like 3.3-hammer. We can discuss whether it is 
now already the right time, and where to make the cut, but medium-term 
we must reduce the number of supported compilers.

> -Andi

cu
Adrian

[2] example: static __init function with exactly one caller, and this
             caller is non-__init

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed

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