Bug 17923 – ARM platform endian defines inaccurate in JavaScriptCore

• Component: JavaScriptCore
• Status: RESOLVED FIXED

[David Krause]

As part of bug 15416 (http://bugs.webkit.org/show_bug.cgi?id=15416), a change was made to JavaScriptCore/wtf/Platform.h that affected when the WTF_PLATFORM_MIDDLE_ENDIAN define is set.  The specific changeset is http://trac.webkit.org/projects/webkit/changeset/31115.

Basically, some ARM platforms that define __ARMEL__ still need the MIDDLE_ENDIAN define.  Specifically, it affects those little-endian ARM platforms using FPA floating-point.  See comment on original bug for more details at http://bugs.webkit.org/show_bug.cgi?id=15416#c15.

The 31115 change causes JavaScript issues on those ARM platforms that no longer have the MIDDLE_ENDIAN define, but need it.  The issue seen is that the JavaScript dtoa function falls into an infinite loop.

[Mark Rowe (bdash)]

How can the other platforms that need MIDDLE_ENDIAN be detected?

[David Krause]

The only recommendation I have was in my previous comment.  I am not sure which defines are present for VFP floating-point, but for FPA the following works:

#elif !defined(__ARM_EABI__) && !defined(__ARMEB__) && defined(__ARMEL__) &&
defined(__SOFTFP__)

Right now, I only have access to my version of gcc, which sets __ARMEL__ and __SOFTFP__ for FPA.

[David Kilzer (:ddkilzer)]

Is there not an __ARMEM__ macro for middle endian systems?

Or is this sufficient (per Bug 15416 Comment #15)?

#elif !defined(__ARM_EABI__) && !defined(__ARMEB__) && defined(__ARMEL__) && defined(__SOFTFP__)

[David Kilzer (:ddkilzer)]

(In reply to comment #2)
> The only recommendation I have was in my previous comment.  I am not sure which
> defines are present for VFP floating-point, but for FPA the following works:
> 
> #elif !defined(__ARM_EABI__) && !defined(__ARMEB__) && defined(__ARMEL__) &&
> defined(__SOFTFP__)
> 
> Right now, I only have access to my version of gcc, which sets __ARMEL__ and
> __SOFTFP__ for FPA.

If this is sufficient, please post a patch with changelog to this bug.  Thanks!

[David Krause]

No __ARMEM__ macro exists.  I'll post a patch as requested.

[David Krause]

Created attachment 19884 [details]
Proposed patch

Found a VFP toolchain, and it also defines __ARMEL__ and __SOFTFP__, so my earlier proposal would not have been appropriate.  __VFP_FP__ is the define that indicates VFP support, which should not use MIDDLE_ENDIAN.

[David Kilzer (:ddkilzer)]

Comment on attachment 19884 [details]
Proposed patch

Looks good!  r=me

[David Kilzer (:ddkilzer)]

Committed revision 31176.