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Re: [patch driver]: Fix relocatable toolchain path-replacement in driver

On Wed, 11 Sep 2013, Kai Tietz wrote:

> This change fixes a quirk happening for relocated toolchains.  Driver
> remembers original-build directory

The original *build* directory should never be known to the driver; only 
the *configured* prefix.

This area is complicated and subtle; you need to be very careful and 
precise in the analysis included in any patch submission related to it.  
Get things absolutely clear in your head and then write a complete, 
careful, precise self-contained explanation of everything relevant in GCC, 
as if for an audience not at all familiar with the code in question.

> in std_prefix variable for being able later to modify path.  Sadly
> this std_prefix variable gets modified
> later on, and so update_path can't work any longer as desired.  This

You don't say what "as desired" is.  prefix.c contains a long description 
of *what* the path updates are, but no explanation of *why* or any overall 
design; it appears to be something Windows-specific.

update_path should, as I understand it, always be called with PATH being a 
relocated path (one that has had the configured prefix converted to the 
prefix where the toolchain is in fact installed, using 
make_relative_prefix, or that doesn't need any relocation, e.g. a path 
passed with a -B option).  In incpath.c, for example, you see how a path 
is computed using make_relative_prefix before update_path is called.  
Thus, it is correct for std_prefix to be the relocated prefix rather than 
the unrelocated one.

If there is a bug, I'd say it's in whatever code is calling update_path 
without having first done the make_relative_prefix relocation on the path 
being passed to update_path.  Thus, it is that caller that you need to 

Joseph S. Myers

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