Re: [RFC] x86: xsave/xrstor support, ucontext_t extensions

From: H. Peter Anvin
Date: Tue May 20 2008 - 14:14:45 EST

Suresh Siddha wrote:

This issue of not-zeroing, is present in only 64bit kernels and for 64bit apps,

64bit app signal handling uses only rt_frame, so we can add an uc_flag for
them and for 32bit apps, kernel was always zero'ing the reserved bits
at the end of _fpstate.

In short, for non-rt frames, they can check the reserved bits at the end
of fpstate frame and for rt-frames (perhaps even for 32bit rt frame handling)
apps can check for uc_flag aswell, for extended state presence. Is this
good enough?

Are we sure about the "always" bit here (I suspect yes, but we may want to double-check at least back to 2.2 or 2.4.)

Anyway, seems reasonable enough to me.

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