Date: Fri, 22 May 2015 17:22:51 -0500
From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Jiri Kosina <jkosina@suse.cz>
Cc: Borislav Petkov <bp@alien8.de>, Ingo Molnar <mingo@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Michal Marek <mmarek@suse.cz>,
        Peter Zijlstra <peterz@infradead.org>, x86@kernel.org,
        live-patching@vger.kernel.org, linux-kernel@vger.kernel.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andy Lutomirski <luto@kernel.org>,
        Denys Vlasenko <dvlasenk@redhat.com>, Brian Gerst <brgerst@gmail.com>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH v4 0/3] Compile-time stack frame pointer validation
Message-ID: <20150522222251.GE20555@treble.redhat.com>
References: <cover.1431966710.git.jpoimboe@redhat.com>
 <20150520103339.GA22205@gmail.com>
 <20150520141331.GA16995@treble.redhat.com>
 <20150520144810.GA10374@gmail.com>
 <20150521205425.GA31662@treble.redhat.com>
 <20150521220158.GH3689@pd.tnic>
 <20150522143212.GB20555@treble.redhat.com>
 <alpine.LNX.2.00.1505222317370.13817@pobox.suse.cz>
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On Fri, May 22, 2015 at 11:18:57PM +0200, Jiri Kosina wrote:
> On Fri, 22 May 2015, Josh Poimboeuf wrote:
> 
> > Hm, alternatives do complicate things a bit.  It *is* a false positive,
> > but not necessarily because its part of an alternative instruction
> > block.
> > 
> > The above code would be patched into memmove(), which is a leaf function
> > because it doesn't call any other functions.  Leaf functions don't need
> > frame pointer logic, so we can ignore them.
> > 
> > If instead the above code were patched into a non-leaf function, we'd
> > have to change it to restore the frame pointer before returning.
> 
> Is this really only a problem of alternatives? How about 
> dynamically-enabled tracepoints?

I think tracepoints are only in C code, right?  stackvalidate only
analyzes asm code, so it's not a concern for this patch set.

And I think tracepoints rely on normal call instructions, so they
shouldn't cause any problems with frame pointers as far as I can tell.

-- 
Josh
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