Messages in this thread | | | Subject | Re: [RFC PATCH] x86/fpu: Don't unconditionally add XFEATURE_MASK_FPSSE on sigentry | From | Dave Hansen <> | Date | Thu, 25 Apr 2019 14:13:05 -0700 |
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On 4/25/19 10:35 AM, Sebastian Andrzej Siewior wrote: > This commit reverts commit 04944b793e18e ("x86: xsave: set FP, SSE bits > in the xsave header in the user sigcontext"). The commit claims that it > is required for legacy applications but fails to explain why this is > needed and it is not obvious to me why the application would require the > FP/SSE state in the signal handler.
Any software that understands XSAVE is OK. I think the legacy software would be that which groks 'fxregs_state, and FXSAVE/FXRSTOR but does not comprehend XSAVE/XRSTOR. *That* software might change fxregs_state in the signal frame, but the lack of XFEATURE_MASK_FPSSE in xfeatures would prevent XRSTOR from restoring it.
That's just a guess, though.
If we care, I think we should just use XSAVE instead of XSAVEOPT and trying to reconstruct the init state in software.
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