680652 - 64-bit big endian support is broken

Status: RESOLVED DUPLICATE of bug 674522

(Core :: JavaScript Engine, defect)

Description

[Aurelien Jarno]

Attachment: Patch to fix the issue

On 64-bit architectures, jsval is represented as an union mapping double, 32- or 64-bit values. It uses the IEEE754 denormalized number representation to encode the type of the variable when it is not a float value. That's why the tag part is exactly at the same place and location than the sign + exponent in  a 64-bit double value, and the payload is exactly at the same place than the mantissa.

However this way only works for little-endian machines. On big-endian machines the payload overrides the sign+exponent and the tag overrides the mantissa. Moreover all the 64-bit macros in jsval.h assume a little endian order.

The attached patch tries to fix that by modifying the jsval layout to make it little-endian (at the 32-bit word level), by swapping the two 32-bit words. For that it uses dummy 32-bit values in an anonymous structure to force the location of the other 32-bit values. With this patch, the JavaScript testsuite gives the same result than on a 64-bit little endian machine (s390x versus x86_64).

Comment 1

[:Ms2ger (he/him; ⌚ UTC+1/+2)]

Are you on the latest version? It seems that this issue should have been fixed in bug 674522 (for Firefox 8).

Comment 2

[Mike Hommey [:glandium]]

Yes, it's the same bug. Aurelien was building 6.0