Re: [Patch, mips]: Add support for FR=1/o32. Update implemention of setjmp/longjmp

["Joseph S. Myers" <joseph at codesourcery dot com>]

On Tue, 26 Nov 2013, Matheus Almeida wrote:

> This patch updates the definition of setjmp, longjmp and jmp_buf so that 
> on a call to setjmp/longjmp, all the required floating-point 
> callee-saved registers are properly saved/restored.
> 
> We are aware that updating the size of jmp_buf can potentially break 
> existing applications but we expect the number of applications built 
> with FR=1 mode to be very small, possibly zero. Nevertheless this should 
> be clearly stated in the release notes that existing applications built 
> with FR=1 (-mfp64) need to be recompiled in order to use new versions of 
> the library.

I don't recall a response to 
<https://sourceware.org/ml/binutils/2013-09/msg00045.html>, and don't see 
one in the binutils list archives.  I believe that just like the NaN 
changes, this needs to be considered as an incompatible ABI variant, with 
ELF header checks in the dynamic linker to ensure that all loaded objects 
are compatible (whether or not you also define new dynamic linker names 
for one or both of o32/-mfp64/legacy-NaN and o32/-mfp64/NaN-2008) - 
incompatibilities should be detected by the dynamic linker, not "need to 
be recompiled".  I suggest looking at Maciej's NaN changes as a model.  
Also as suggested in that message to the binutils list, I think *context 
functions need updating as well as setjmp/longjmp, and there should be an 
ABI supplement document explaining o32 function call and return for 
-mfp64.

What's the kernel.org kernel version with support for this feature (that 
is, the kernel that checks the ELF header flag and ensures the FPU is 
correctly set up for the process)?  As with NaN-2008, arch_minimum_kernel 
should be set to the appropriate kernel version, or 10.0.0 until the 
relevant support is in the kernel.org tree.

-- 
Joseph S. Myers
joseph@codesourcery.com