On 27/11/13 17:11, Paul Burton wrote: > On 21/11/13 19:52, Maciej W. Rozycki wrote: >> I think the discussion was off-list (Ralf, would you mind if I digged up >> any clues from there?). The format has been set long ago, and is also odd >> enough to have 32 64-bit slots in the PTRACE_GETFPREGS/PTRACE_SETFPREGS >> structure even for o32 processes (that now should be unexpectedly helpful >> for FP64 o32 processes though), so there's little sense discussing its >> prettiness or ugliness at this point in the game. >> >> Also I'm not sure what the core file format is for the FP context, it may >> be worth double-checking too. >> >> Please feel free to poke me directly if you have any further issues about >> MIPS I ISA compatibility. > > Ok I finally had time to look at this. It seems that r2300_switch.S used > to match the current behaviour of r4k_switch.S. Ralf made it that way by > saving to the appropriate 32 bits of the even numbered 64 bit values of > the FP context, taking endianness into account, in the following commit: > > http://git.linux-mips.org/?p=ralf/linux.git;a=commitdiff;h=42533948caacb82574ccf91cae84df851d4f0521#patch28 > > ...and then you fixed up ptrace to always expect values stored in the > format now used by r4k_switch.S (& at the time used by r2300_switch.S too): > > http://git.linux-mips.org/?p=ralf/linux.git;a=commitdiff;h=849fa7a50dff104cbf6654c421b666eefd6da0c1;hp=364e85467c9c08c803087c5b75ae2e70540e3bb5 > > Unfortunately later when Ralf replaced the FPU_SAVE_SINGLE macro with > the fpu_save_single macro in this commit: > > http://git.linux-mips.org/?p=ralf/linux.git;a=commitdiff;h=bf0b3bb876115b1e69b2266477128d8270d0b356;hp=39507fed032849b72552062883d143025be8be36 > > ...he effectively reverted r2300_switch.S to its old behaviour, whilst > ptrace continues to expect the r4k_switch.S-like behaviour. So as far as > I can tell the original intended FP register layout was that currently > used by r4k_switch.S. That makes r2300_switch.S the incorrect one - > fixed 11 years ago & broken again 10 years ago. > > What I'm less sure about right now is what gdb has come to expect in the > meantime - but from your description it sounds like it expects the > r2300_switch.S behaviour? In which case I suspect that although it seems > the original intended ptrace ABI was broken long ago & the easiest fix > may be for the kernel to just go with the unintended ABI on r4k-class > cores too? I'll have a read through more gdb code & try to confirm. Maciej: are you sure this is working correctly with r2300_switch.S? gdb seems to be working as I'd expect with r4k_switch.S and I have no r2k/r3k hardware to test on. Thanks, Paul
