gcc version 4.6.0 20100908 (experimental) (GCC) Fails to Build Python 2.7

Tom Browder tom.browder@gmail.com
Tue Sep 21 01:44:00 GMT 2010


On Mon, Sep 20, 2010 at 16:12, Ian Lance Taylor <iant@google.com> wrote:
> Tom Browder <tom.browder@gmail.com> writes:
>
>> On Fri, Sep 17, 2010 at 16:42, Tom Browder <tom.browder@gmail.com> wrote:
>>> On Fri, Sep 17, 2010 at 06:05, Tom Browder <tom.browder@gmail.com> wrote:
>>>> The subject says it all.  The build works with released gcc version
>>>> 4.5.1.  The Python folks say that a pyc file gets corrupted somehow.
>>
>> As a next debugging step I plan to try to compare asm output for the
>> source files in question, but is it a waste of time for a novice due
>> to too many changes between compiler versions?
>
> Probably, yes.
>
>> Looking for any help or hints in the proper direction to head for debugging.
>
> If you have a repeatable test case, study it until you understand
> exactly why it fails.  This often means running it under the debugger
> over and over again.  I don't know of any good way to skip this step.
>
> If you don't have a repeatable test case, then you could try a hail mary
> like comparing asm output, but I wouldn't hold out much hope.
>
> 9 times out of 10 breaking with a new compiler version is due to a case
> where the code relies on behaviour that is undefined according to the C
> standard, and where some compiler optimization has become more
> aggressive.  1 time out of 10 it is a compiler bug.  So one approach is,
> once you have a general idea of which code is behaving badly, look at it
> to see if there are any potential aliasing violations or cases where the
> code depends on defined signed overflow.

Thanks, Ian--that helps.

-Tom



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