Re: [libunwind] libunwind-bk on x86-64

[Arun Sharma]

rajagopal, dwarak wrote:

> 1) But, I don't understand why FPU should be used before the signal is
> raised? Is this something to do saving fpu registers between context
> switching because the OS won't save fpu registers during context
> switching by default unless they are used. 

Linux uses a lazy floating point save/restore algorithm to optimize 
context switch times. It also doesn't save the FPU state into the 
sigcontext if the task hasn't used it.

So yes, different code paths in the kernel would be excersized depending 
on whether the task did or did not use FPU. But I'm not sure why the 
lazy FP algorithm would interfere with the unwind library.

        -Arun