linux-kernel - [PATCH] uprobes: Document xol_area and arch

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Message-ID: <20131119162545.GA776@redhat.com>
Date:	Tue, 19 Nov 2013 17:25:45 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] uprobes: Document xol_area and arch_uprobe->insn/ixol

On 11/11, Ingo Molnar wrote:
>
> * Oleg Nesterov <oleg@...hat.com> wrote:
>
> > On 11/11, Ingo Molnar wrote:
> > >
> > > You guys are changing code that reads like gobbledygook to people
> > > reading it for the first time.
> >
> > Not that I am trying to defense uprobes, but this is equally true for
> > any piece of kernel code, at least to me ;)
>
> I'm really not suggesting to do overly much - only for some minimal blurb
> like the scheduler has in most places:

OK. Let me try to make a first step to improve this a little bit...

How about the patch below? Srikar?


Subject: [PATCH] uprobes: Document xol_area and arch_uprobe->insn/ixol

Document xol_area and arch_uprobe.

Signed-off-by: Oleg Nesterov <oleg@...hat.com>
---
 kernel/events/uprobes.c |   15 +++++++++++++++
 1 files changed, 15 insertions(+), 0 deletions(-)

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 51a7f53..b886a5e 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -73,6 +73,17 @@ struct uprobe {
 	struct inode		*inode;		/* Also hold a ref to inode */
 	loff_t			offset;
 	unsigned long		flags;
+
+	/*
+	 * The generic code assumes that it has two members of unknown type
+	 * owned by the arch-specific code:
+	 *
+	 * 	insn -	copy_insn() saves the original instruction here for
+	 *		arch_uprobe_analyze_insn().
+	 *
+	 *	ixol -	potentially modified instruction to execute out of
+	 *		line, copied to xol_area by xol_get_insn_slot().
+	 */
 	struct arch_uprobe	arch;
 };
 
@@ -86,6 +97,10 @@ struct return_instance {
 };
 
 /*
+ * Execute out of line area: anonymous executable mapping installed
+ * by the probed task to execute the copy of the original instruction
+ * mangled by set_swbp().
+ *
  * On a breakpoint hit, thread contests for a slot.  It frees the
  * slot after singlestep. Currently a fixed number of slots are
  * allocated.
-- 
1.5.5.1


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