Re: [gentoo-user] gcc-4.1.1

["Thomas T. Veldhouse" <veldy@veldy.net>]

Bob Young wrote:
>   
>> -----Original Message-----
>> From: richard.j.fish@gmail.com [mailto:richard.j.fish@gmail.com]On
>> Behalf Of Richard Fish
>> Sent: Wednesday, June 07, 2006 9:24 PM
>> To: gentoo-user@lists.gentoo.org
>> Subject: Re: [gentoo-user] gcc-4.1.1
>>
>>
>> On 6/7/06, Bob Young <BYoung@nucoretech.com> wrote:
>>     
>>> chain. At the end of the first emerge -e system you may have a
>>>       
>> new compiler,
>>     
>>> but that new compiler was built with the old compiler.
>>>       
>> This is false.  Gcc uses itself to build itself.  It uses the system
>> compiler to build an initial version of itself, and then uses that
>> version to build itself.  And then for good measure, it uses that
>> version to build the final version.  It's called a 3-stage bootstrap,
>> and is documented in the file INSTALL/build.html in the gcc sources.
>> You can also look at /usr/portage/eclass/toolchain.eclass to determine
>> that Gentoo uses the "bootstrap-lean" target by default.
>>     
>
> No, sorry that's just wrong. gcc is slotted, if the above were true there
> would be no need for gcc-config in order to select a default compiler. When
> a new compiler is emerged, it does *not* automatically become the default
> system compiler, it must be selected, and that can only happen after it has
> successfully been emerged. The first time a new gcc compiler is emerged, it
> is indeed built with the previous version of the compiler that is currently
> istalled as the system default.
>   
xgcc is built with the previous system compiler.  Then xgcc is used to 
build the new gcc for installation.  The final install is a self-built 
gcc and is not built by the previous system compiler.
>
>   
>> Frankly, anybody who claims that gcc needs to be merged twice so it
>> can be built with itself and produce better object code does not have
>> a clue what they are talking about and you should simply disregard
>> anything else they have to say about what is necessary/useful when
>> upgrading gcc.
>>     
>
> It does have to be emerged twice in order for it to be built with itself,
> anybody who thinks otherwise doesn't understand the basic principles of
> compiling and linking.
>   
I think you have ignored what the previous poster suggested.
>   
>>> happen before glibc is rebuilt are linked against a glibc that was built
>>> with the old compiler.
>>>       
>> And guess what difference this makes to the end result.  None.
>> Nada.  Nothing.
>>
>> Because for basically every program on your system, they are
>> *dynamically linked* against glibc.
>>     
>
> Are you absolutely 100% sure that every single system utility and
> application is *dynamically* linked, and that no apps or utilities anywhere
> in the system specifies *static* linking?
>
>   
>> There are a few statically linked programs that will include glibc
>> internally.  These are used only for system recovery purposes...there
>> is no need to worry about them at all.
>>     
>
> Really, so people who intentionally and specifically want to upgrade
> absolutely *everything* should not worry about what gets left out because
> Richard says it's unimportant?
>
> The issue is about upgrading gcc and even the gcc upgrade howto recommends
> an emerge -e world. It's clear that gcc it self at least has to be emerged
> twice in order to build the new gcc *with* the new gcc. 
Wrong.  The gcc package builds a bootstrap compiler (the new version), 
called xgcc and then it uses that to build [after some tests] the final 
installed gcc.  A single emerge of gcc will create a compiler that was 
built by itself.

Thus, if you move from 3.3.4 to 4.1.0:

emerge -u gcc

You WILL have a gcc that was compiled by a 4.1.0 compiler.

> Whether this is
> strictly necessary or not is certaintly debatable, but since it executes
> fairly quickly, and seems a prudent step, I'd argue that it's a reasonable
> course. Of course a selecting the new gcc as the default with gcc-config is
> also required in between, but that's self evident. Adding gcc-config, glibc,
> binutils, libstdc++-v3, quickly covers the most important parts of the basic
> tool chain, and covers most utilities or apps that might specify static
> linking, and executes much much faster than an emerge -e system.
>
>   
>> There is no value to having glibc or libstdc++-v3 in the first line.
>> There is no value at all to doing that twice.
>>     
>
> Twice is the only way to build the new gcc *with* the new gcc. I should have
> added the gcc-config select command in between, but I thought that was
> pretty clearly necessary.
>
>   
You didn't pay attention to what he wrote.  I hope perhaps my post made 
it more clear.

Tom Veldhouse


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