linux-kernel - semantics of KSTK

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Date:	Thu, 12 Feb 2015 07:10:06 +0000
From:	Vineet Gupta <Vineet.Gupta1@...opsys.com>
To:	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	james Hogan <james.hogan@...tec.com>
CC:	Alexey Brodkin <Alexey.Brodkin@...opsys.com>,
	al Viro <viro@...IV.linux.org.uk>,
	lkml <linux-kernel@...r.kernel.org>
Subject: semantics of KSTK_ESP and friends

Hi,

Is KSTK_ESP supposed to return the kernel mode SP of a sleeping task or is it supposed to provide the user mode SP at the time of last kernel entry ?

The 2 non arch users of the API expect the user mode SP semantics:
* vm_is_stack_for_task() - to annotate /proc/<pid>/maps stack vma - which is shere Alexey noted this.
* do_task_stat()

ARC port uses these for unwinding the task of a sleeping task (hence kernel mode SP semantics).
metag (from the looks of it) also seem to provide kernel mode value, while most others seem to provide the user mode variant.

 I can fix ARC to work with expectation of generic code, but wanted to understand anyways.

Thx,
-Vineet
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