403783 - nsIBinaryStream has trouble writing and reading double floats

Status: NEW

(Core :: XPCOM, defect, P3)

Description

[Alex Vincent [:WeirdAl]]

Spun off of bug 401781 - I'd written a test for binary streams.  The test detected a strange bustage on Linux machines, SeaMonkey and Firefox.  Reproducing the bug is difficult according to bz...

Steps to reproduce:
(1) Uncomment these marked lines:
http://bonsai.mozilla.org/cvsblame.cgi?file=mozilla/xpcom/tests/unit/test_streams.js&rev=1.4&mark=89-90,119,138#89
(2) make check

Comment 1

[Damon Sicore (:damons)]

What does this impact?  Before we'll plus this, we need to know what this is used for, what it breaks, etc.

Comment 2

[Alex Vincent [:WeirdAl]]

http://lxr.mozilla.org/seamonkey/search?string=readDouble
http://lxr.mozilla.org/seamonkey/search?string=writeDouble

I can't find any evidence readDouble and writeDouble are being used by anyone other than test code.  I requested blocking1.9 based on the informal conversation on 11/13 in #developers about this issue.

Comment 3

[Alex Vincent [:WeirdAl]]

Couldn't reproduce on Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9b2pre) Gecko/2007111501 Minefield/3.0b2pre - Fedora 7.

I would imagine that's not too different from the reference platform:
http://wiki.mozilla.org/ReferencePlatforms/Linux-CentOS-5.0

Comment 4

[Damon Sicore (:damons)]

-'ing.  If we can determine what uses readDouble and writeDouble and it's an issue, please re-nom.

Comment 5

[Alex Vincent [:WeirdAl]]

qawanted: can anyone reproduce this?  (Note bug 403992, which is to try getting access to a tinderbox clone.)

Comment 6

[Sylvain Pasche]

I can reproduce. This is related to bug 408258 comment 4: Using -fstrict-aliasing (enabled at -O2) breaks nsBinaryOutputStream::writeDouble() here and nsBinaryOutputStream::writeFloat() in bug 409881 (x86_64).

I noticed that adding a printf() call in the beginning of nsBinaryOutputStream::writeDouble or nsBinaryOutputStream::writeFloat fixes the problem, too.

Comment 7

[Alex Vincent [:WeirdAl]]

I would humbly suggest removing readDouble, writeDouble.  Again, no one is currently using them in the Mozilla code base, and they have known test failures.

Comment 8

[Sylvain Pasche]

note that something like bug 408258 comment 7 could fix the issue.