Would it make sense to have sysroot come from an environment variable?

[Bryan Ischo]

On 08/26/11 13:56, Ian Lance Taylor wrote:
> Bryan Ischo<bryan@ischo.com>  writes:
>
>> Thank you for your reply.  So just to be clear, are you saying that I
>> would configure gcc --with-sysroot=DIR, and then at runtime I can do:
>>
>> $ mv DIR DIR.moved
>> $ /some/random/path/to/gcc
>>
>> And that gcc, which was installed in a place that had nothing to do
>> with DIR, will somehow know that I moved DIR?  How does it do that?
> Yes, that is what I am saying.  The key is that gcc itself is under
> DIR--it's in DIR/bin.  It looks at argv[0] to see where it was run from.
>
> Ian

Now I'm really confused.  My example doesn't have gcc under DIR; it's 
under /some/random/path/to/gcc.  sysroot is for header files and 
libraries, or at least that's how it's described in all documentation I 
have read.  Here is what the gcc manual says about --sysroot:

"|--sysroot=|dir
     Use dir as the logical root directory for headers and libraries. 
For example, if the compiler would normally search for headers in 
/usr/include and libraries in /usr/lib, it will instead search 
dir/usr/include and dir/usr/lib. ..."

Why would gcc be under sysroot if sysroot is for include files and 
libraries?

Also, isn't looking at argv[0] to see where an executable was run from 
generally bad practice on Unix?  You can't always know with certitude 
where a program was run from just by looking at argv[0], and the 
techniques that are often used to take argv[0] and turn it into an 
absolute path are typically nonportable, not guaranteed to work, and 
generally suspect.  Or at least that's how I understand it ...

And finally, for a cross-compiler, how would gcc ever be under DIR 
anyway?  DIR is the root of a subtree containing include files and 
libraries for the $TARGET platform, whereas gcc itself is run on the 
$HOST platform; it is counter-intuitive to me that a directory 
containing include files and libraries for $TARGET platform would have 
binaries under bin meant to run on $HOST platform ...

Thanks,
Bryan