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Date: Thu, 19 Dec 2002 11:37:06 -0800 (PST)
From: Linus Torvalds <torvalds@transmeta.com>
To: bart@etpmod.phys.tue.nl
cc: davej@codemonkey.org.uk, <lk@tantalophile.demon.co.uk>,
       <hpa@transmeta.com>, <terje.eggestad@scali.com>, <drepper@redhat.com>,
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Subject: Re: Intel P6 vs P7 system call performance
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On Thu, 19 Dec 2002 bart@etpmod.phys.tue.nl wrote:
> 
> True, but unless I really don't get it, compatibility of a new static
> binary with an old kernel is going to break anyway. 

NO.

The current code in 2.5.x is perfectly able to be 100% compatible with 
binaries even on old kernels. This whole discussion is _totally_ 
pointless. I solved all the glibc problems early on, and Uli is already 
happy with the interfaces, and they work fine for old kernels that don't 
have a clue about the new system call interfaces.

WITHOUT any new magic system calls.

WITHOUT any stupid SIGSEGV tricks.

WITHOUT and silly mmap()'s on magic files.

> My point was that the double-mapped page trick adds no overhead in the
> case of a static binary, and just one extra mmap in case of a shared
> binary.

For _zero_ gain.  The jump to the library address has to be indirect 
anyway, and glibc has several places to put the information without any 
mmap's or anything like that.

		Linus

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