svn commit: r216977 - in head/libexec/rtld-elf: amd64 i386

[Nathan Whitehorn]

On 01/05/11 08:28, John Baldwin wrote:
> On Wednesday, January 05, 2011 8:36:06 am Dimitry Andric wrote:
>> On 2011-01-05 13:59, John Baldwin wrote:
>>>> Why not to add NO_HWFLOAT knob (or similar) into makefile
>>>> infrastructure. And set CFLAGS accordingly, depending on CC, arch, etc.
>>>> These flags are getting rather common in tree.
>>> It strikes me that we really want clang/gcc to have some sort of
>>> '-mno-hwfloat' so we don't keep having to add new flags in the future.
>> This is not just about floats, clang can also use SSE/AVX instructions
>> for e.g.  memset(), memcpy() and the like, or even for structure
>> assignments.
> Yes, but the thing that all these extensions have in common is that they use
> FPU state (i.e. subject to DNA traps, managed via *SAVE and *RSTOR, etc.)
> and that is the problem with using them in boot code or rtld.  What I would
> want a -mno-hwfloat flag to do is to disable use of anything that would
> require working FPU state handling.

You would also want this to be cross-platform, in which case it's more 
than floating point. E.g. on powerpc, you also want to disable both FP 
and vector extensions, which use separate sets of instructions and 
registers. I guess overriding CPU type to be something very old (386?) 
potentially deoptimizes the code?
-Nathan