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


From: Arun Sharma
Subject: Re: [libunwind] libunwind-bk on x86-64
Date: Mon, 23 Jan 2006 16:06:16 -0800
User-agent: Mozilla Thunderbird 1.0.7 (X11/20051011)

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

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