I made it to the floating point math chapter in my book and discovered that ebe was showing 0's for the xmm registers and wouldn't display the ymm registers. I checked and a program which loaded 3.25 into xmm0 ended up with xmm0.v4_float = {0.0, 0.0, 0.0, 3.25} while the same program under Linux shows it as {3.25, 0.0, 0.0, 0.0}. I don't think the CPU has an option for reversing the order of the floating point values in the xmm registers.
I checked the version for gdb and found that I was using 6.3 under OS X and 7.5 under Linux, so I checked MacPorts and 7.5 is available, so I installed it. Then the fun began. It must be codesigned which requires greating a code signed certificate. I have done that and signed it still fails to run with this message when I try the run command on a program:
Unable to find Mach task port for process-id 58919: (os/kern) failure (0x5).
(please check gdb is codesigned - see taskgated(8))
The more I poke at OS X the less I like it. Installing gdb is trivial under Linux. Is there some extra permission involved with Linux? I doubt it, but at least it just works.
Just for grins I did "sudo gdb fpadd" and it now lets the program run, though I get a slew of BFD unknown load command errors.
I will return to this later when I know more.
Well, 1 day later and no closer to understanding this nonsense. I have managed to run gdb 7.5 which solves the problem with the xmm register values being reversed. I still have problems running gdb as seyfarth instead of root. I tried installing a newer version of gcc which does not help. For my test code I am linking with gcc so it seems possible that some linker options might result in an exe file which gdb recognizes as having a need for avx support.
I suppose I will get this solved, but will I end up with a clearly defined way for people to configure their own Macs to support floating point properly with ebe? I think I will refrain from entering a complete discussion in the book and refer to a web site so that I can adjust the description as I learn more.
After a couple more days of poking around I have reached a decision. I have implemented a xmm:reverse ini parameter which will allow someone who is using a "defective" gdb to see the xmm registers properly. I expect that in a few months OS X will have an easily installable gdb with proper xmm/ymm register support. I will point out that there is a problem with some versions of gdb in the book and suggest where to look on my web site for further information.
I did find a workable solution using the lldb debugger which comes with xcode. This would make ebe unnecessarily complex for a few months. There would be enough changes to make it likely that there would be additional bugs. I decided to exercise a little patience. No matter which choice I made I would have to document it in the book. Using the gdb which came with xcode makes it less trouble to use at the cost of setting a value in .ebe.ini.
