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
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