linux-kernel - RE: [patch] x86: ptrace and core-dump extensions for xstate

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Message-Id: <20100204045458.5AA2F7290@magilla.sf.frob.com>
Date:	Wed,  3 Feb 2010 20:54:58 -0800 (PST)
From:	Roland McGrath <roland@...hat.com>
To:	"Lu, Hongjiu" <hongjiu.lu@...el.com>
Cc:	"Siddha, Suresh B" <suresh.b.siddha@...el.com>,
	Oleg Nesterov <oleg@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	"Lachner, Peter" <peter.lachner@...el.com>
Subject: RE: [patch] x86: ptrace and core-dump extensions for xstate

> To support XSAVE, gdb needs to know XCR0 as well as XSTATE size.
> We can get those info from kernel via system call or cpuid. I
> prefer cpuid over system call.

Suresh's patch puts this value in the xsave block, in what Suresh calls
"sw_usable_bytes".  See the asm/ptrace-abi.h comment in the patch you
signed off on.

How is that not sufficient?  If it is indeed not sufficient to usefully
interpret the xsave block, then how could an xsave block in a core dump
file ever possibly be examined if it might not have been generated on the
same system and kernel where the debugger is doing the examination?  If
the NT_X86_XSTATE note as implemented in Suresh's patch is indeed not
entirely self-contained in this way, then NAK on that new note format.

Thanks,
Roland
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