Re: Making gcc -no-canonical-prefixes the default?

[Simon Baldwin <simonb at google dot com>]

On 31 January 2011 01:20, Gerald Pfeifer <gerald@pfeifer.com> wrote:
> On Fri, 28 Jan 2011, Ian Lance Taylor wrote:
>> Some archealogy turned up this as the reason canonicalization was
>> inserted:
>>
>> http://gcc.gnu.org/ml/gcc/2003-02/msg01121.html
>> http://gcc.gnu.org/ml/gcc-patches/2003-02/msg01697.html
>>
>> Also relevant here is http://gcc.gnu.org/PR29931 .
>
> I am quite sure that the current behavior where one can have a symlink
> point to an installation of GCC anywhere else (outside of any path even)
> has been in place for quite a bit longer than 2003.

Thanks for the notes and archaeology.  My guess is that because it's
easier, symlinking a single gcc binary is more common than symlinking
a complete gcc tree.


> On Sat, 29 Jan 2011, Dave Korn wrote:
>> I think the case which is particularly common is the alternatives
>> system, which has a chain of symlinks finally pointing to a real gcc.
>> (That works just fine with the current default, AFAIK, although that
>> may be only because the real gcc is in $PATH?)
>
> Nope, only the symlink(s) need to be in the path. ?And indeed this
> usecase that you and also Joseph describe is how I've been using it
> for many years.
>
> Given that this has een default behavior for so long (more than a
> decade from what I can tell), I'd recommend not changing it.

That would be as good a reason as any for not changing it.  Thanks for
the clarification.

The patch in http://gcc.gnu.org/PR29931 uses... heuristics to detect
if the gcc driver is a single symlink or part of a symlink farm
(Florian Weimer's suggestion above).  The patch has never been fully
accepted, though; any known reason?  I believe it will handle the two
main use cases reliably.  Combining it with -[no-]canonical-prefixes
flags as overrides would cover all cases unambiguously.

If heuristics aren't deemed reliable enough, another option is to set
a default with a -no-canonical-prefixes-default configure flag.  Less
flexible because it's baked in to gcc, but simpler.

On balance the PR29931 patch approach with -[no-]canonical-prefixes
overrides seems to me like it will lead to least trouble in future.
It also closes a long-standing gcc PR.  Any dissent?  Other options?

Thanks.

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