Re: [PATCH 5/6] ld.so.8: document $PLATFORM and $LIB expansion

[Mike Frysinger <vapier-aBrp7R+bbdUdnm+yROfE0A@public.gmane.org>]

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On Friday 21 October 2011 01:25:28 Jonathan Nieder wrote:
>  - what is $LIB for a non-native ABI?

whatever it's been configured for.  it isn't an env var that is the same across 
all ABIs.  you could configure every ABI to use /lib, but that'd be dumb.

if we look at the 3 ABI's we have on the x86 system and their standard install 
paths:
	- 32bit: lives in /lib and has ldso at /lib/ld-linux.so.2
	- 64bit: lives in /lib64 and has ldso at /lib64/ld-linux-x86-64.so.2
	- x32: lives in /libx32 and has ldso at /libx32/ld-linux-x32.so.2

you don't `./configure && make` once to get multiple ABIs.  you have to 
manually run that per ABI.  so the 32bit ABI gets configured so $LIB is set to 
/lib, then the 64bit ABI gets configured for /lib64, etc...

the ldso at runtime will replace $LIB with whatever it was configured for

>  - does anyone customize this to point somewhere else and make their
>    machine non-FHS-compliant?  Maybe NixOS and Gentoo Prefix do.

you can't really consider Gentoo Prefix as a being the domain of FHS rule.  it 
is not a distro you boot ... it's a set of packages you build/install into 
your $HOME because your host system is old/broken/whatever.

>    What would a person typically use ${LIB} in an rpath for?

it's useful when you want to preload a library for multiple process types.  
why this would get used in an RPATH tag, i can't really guess since the ELF 
itself is already configured for a specific ABI.  maybe someone more inventive 
can come up with something ;).
-mike

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