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

Ian Lance Taylor iant@google.com
Mon Sep 20 21:23:00 GMT 2010

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.


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