Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:18 as permitted sender) client-ip=2620:137:e000::1:18;
Date:   Wed, 2 Mar 2022 20:39:36 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>
Cc:     alexei.starovoitov@gmail.com, alyssa.milburn@intel.com,
        andrew.cooper3@citrix.com, hjl.tools@gmail.com,
        joao@overdrivepizza.com, jpoimboe@redhat.com,
        keescook@chromium.org, linux-kernel@vger.kernel.org,
        mark.rutland@arm.com, mbenes@suse.cz,
        Masami Hiramatsu <mhiramat@kernel.org>,
        ndesaulniers@google.com, rostedt@goodmis.org,
        samitolvanen@google.com, x86@kernel.org
Subject: Re: [PATCH v2 15/39] x86/ibt,kprobes: Fix more +0 assumptions
Message-ID: <Yh/H+IyKnnC0w5TN@hirez.programming.kicks-ass.net>
References: <20220224151322.892372059@infradead.org>
 <20220228150705.aab2d654b973109bab070ffe@kernel.org>
 <20220228232513.GH11184@worktop.programming.kicks-ass.net>
 <20220301114905.e11146ad69d6e01998101c3b@kernel.org>
 <Yh3ZQQv8GjtqgUF4@hirez.programming.kicks-ass.net>
 <1646154463.4r1sh4kjf0.naveen@linux.ibm.com>
 <20220301191245.GI11184@worktop.programming.kicks-ass.net>
 <20220301200547.GK11184@worktop.programming.kicks-ass.net>
 <1646236764.vx04n8yp12.naveen@linux.ibm.com>
 <Yh/GXaqzDNfp93Jd@hirez.programming.kicks-ass.net>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <Yh/GXaqzDNfp93Jd@hirez.programming.kicks-ass.net>
Precedence: bulk

On Wed, Mar 02, 2022 at 08:32:45PM +0100, Peter Zijlstra wrote:
> I wonder if you also want to tighten up on_func_entry? Wouldn't the
> above suggest something like:
> 
> kprobe_opcode_t *arch_adjust_kprobe_addr(unsigned long addr, unsigned long offset,
> 					 bool *on_func_entry)
> {
> #ifdef PPC64_ELF_ABI_V2
> 	unsigned long entry = ppc_function_entry((void *)addr) - addr;
> 	*on_func_entry = !offset || offset == entry;
> 	if (*on_func_entry)
> 		offset = entry;
> #else
> 	*on_func_entry = !offset;
> #endif
> 	return (void *)(addr + offset);
> }

One question though; the above seems to work for +0 or +8 (IIRC your
instructions are 4 bytes each and the GEP is 2 instructions).

But what do we want to happen for +4 ?