SecondLife on SPARC
By Danaf-Oracle on Jul 11, 2007
OK, now back to SecondLife. After deciding to go with gccfss, I still had data alignment to deal with. Alexey Starovoytov came to the rescue advising me to add
asm("ta\\t6"); to SL's
main(). This little trick enables a corrective trap handler on SPARC that will fix unaligned references. For those who need a deeper definition, John Harres provided the following:
Since this is a user land trap, it ends up in the user side of the trap table, which effectively adds 0x100 to the trap number. This ends up in:
GOTO(.fix_alignment); /\* 106 do unaligned references \*/
in the trap table. It ends up setting p_fixalignment in the proc structure, which then is noticed during trap() if you're taking a T_SYS_RTT_ALIGN trap from user land. WIth that flag set this results in the call to do_unaligned(). Therefore, each time the program takes an alignment trap, do_unaligned() is called. One would expect the overhead to be rather minimal unless one is doing a lot of unaligned references.
I can't thank Alexy and John enough for their help.
Once I got passed the alignment problems I then ran up against Open GL Library issues on SPARC. The SL deveopers assume the GLext, originally called the GL Extensions for Linux Library, exists. Well currently on SPARC GLext does not and at the moment I've
#ifdef'ed around these calls to get a clean compile and wound up making the viewer ugly. This is what I'll be attacking next.
Here's a few other things that were done to the Viewer for Solaris compatibility:
All the libraries required by the viewer but not bundled with Solaris were built for the SPARC using the same methods described for the x86 port. They were then copied into the
linden/libraries/sparc-sunos5directory for the SCONS build.
The Lindens have dedicated pages of source to figuring out the type of x86 processor is in use. Instead of using their assembler calls and because said assembler does not apply to SPARC I used
getisax(2)to extract the cpu info. The cpu kstats were used to determine the processor brand and clock rate while on x86/x64, getisax(2) was used to further define which CPU extensions were in use.
- The in window color depth was reduced from 32 to 24 bits on SPARC to allow compatibility with more of the frame buffers available on SPARC.
- The Viewer assumes the X.org X-Window System server. It currently references the X.org server logs to determine how much memory is configured on the GPU. A true kludge. On SPARC X.org is not yet supported so this code is useless and it's ignored. According to its documentation the SDL library provides such information but when one inspects the SDL source one finds the variable but discovers it's not ever set. Doh! Therefore for now, the viewer assumes the maximum amount of memory is available, the default action when it can't be determined by any other means.
One of the largest stumbling blocks was big endian conversions on SPARC. I spent weeks trying to band-aid my way through fixes. Then last week, as he was adding the Solaris changes to the master repository at Linden Labs, Soft Linden discovered that a header file was missing from one of their message passing sources - a LL bug that I missed. That header was the one that defined
LL_BIG_ENDIAN. Once I added that include everything fell together and I proceeded to rip out my endian changes. Without Soft's help I would have wasted a ton of more time "fixing things". Thanks Soft!
- The SL community has offered an openal alternative to the FMOD audio library. Using the patches offered for openal I was able to add audio support to Solaris. There is a rumor that there may be an FMOD available for Solaris in the near future so that option may be viable soon as well.
Lastly, I got approval from Sun Legal to sign the Linden Labs Contributor Agreement and am now officially able to give LL copies of the Solaris patches. I was asked not to distribute any 3rd party libraries outside Sun so I'm hoping someone else will build a version for general distribution. Soft Linden has been working with me to merge those changes into the official SVN repository so they should be available to everyone soon.
If you are interested in building the SL viewer on your own, you should start by reviewing the pages at the SecondLife Open Source Portal.