Re: Perl IPC::Open3 bug, affects apt-get, compiler issue?
* Nicholas Clark <nick@unfortu.net> [020617 13:32]:
>
> Does debug-perl get compiled with -g and no optimiser? In which case, does
> that mean that gcc does all the floating point via loads and stores to
> memory, whereas normal perl is optimised and some floating point values
> stay in the emulators registers?
> (Which I am assuming are 80 bit rather than just the 64 which would be written
> to memory)
No differences in compile flags for perl and debug-perl, except:
nw:~# perl -V > perl.txt
nw:~# debugperl -V > debugperl.txt
nw:~# diff -u perl.txt debugperl.txt
--- perl.txt Mon Jun 17 13:47:29 2002
+++ debugperl.txt Mon Jun 17 13:47:38 2002
@@ -28,9 +28,9 @@
Characteristics of this binary (from libperl):
- Compile-time options: USE_LARGE_FILES
+ Compile-time options: DEBUGGING USE_LARGE_FILES
Built under linux
- Compiled at Jan 17 2002 09:02:54
+ Compiled at Jan 17 2002 09:45:34
@INC:
/usr/local/lib/perl/5.6.1
/usr/local/share/perl/5.6.1
But maybe -DDEBUGGING includes -g?
> You can get similar surprising effects on x86 when floating point
> values do (or don't) get stored to memory - while they are in the CPU
> they are 80 bit, but if they are written to memory (such as when
> passed as parameters to a function) two values that were unequal are
> now equal, due to the rounding. But that's a bug in the user code, whereas
> this would appear to be a subtle bug in FastFPE.
>
> Nicholas Clark
That sounds like a good explanation to what's happening.
Tony
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