From: Miroslav Benes <mbenes@suse.cz>
To: Michael Ellerman <mpe@ellerman.id.au>
Cc: linuxppc-dev@ozlabs.org, bsingharora@gmail.com, duwe@lst.de,
linux-kernel@vger.kernel.org, rostedt@goodmis.org,
kamalesh@linux.vnet.ibm.com, pmladek@suse.com, jeyu@redhat.com,
jikos@kernel.org, live-patching@vger.kernel.org
Subject: Re: [PATCH 2/5] livepatch: Allow architectures to specify an alternate ftrace location
Date: Thu, 14 Apr 2016 14:01:20 +0200 (CEST) [thread overview]
Message-ID: <alpine.LNX.2.00.1604141354130.10605@pobox.suse.cz> (raw)
In-Reply-To: <1460552003-15409-3-git-send-email-mpe@ellerman.id.au>
On Wed, 13 Apr 2016, Michael Ellerman wrote:
> When livepatch tries to patch a function it takes the function address
> and asks ftrace to install the livepatch handler at that location.
> ftrace will look for an mcount call site at that exact address.
>
> On powerpc the mcount location is not the first instruction of the
> function, and in fact it's not at a constant offset from the start of
> the function. To accommodate this add a hook which arch code can
> override to customise the behaviour.
>
> Signed-off-by: Torsten Duwe <duwe@suse.de>
> Signed-off-by: Balbir Singh <bsingharora@gmail.com>
> Signed-off-by: Petr Mladek <pmladek@suse.com>
> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
> ---
> kernel/livepatch/core.c | 34 +++++++++++++++++++++++++++++++---
> 1 file changed, 31 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
> index d68fbf63b083..b0476bb30f92 100644
> --- a/kernel/livepatch/core.c
> +++ b/kernel/livepatch/core.c
> @@ -298,6 +298,19 @@ unlock:
> rcu_read_unlock();
> }
>
> +/*
> + * Convert a function address into the appropriate ftrace location.
> + *
> + * Usually this is just the address of the function, but on some architectures
> + * it's more complicated so allow them to provide a custom behaviour.
> + */
> +#ifndef klp_get_ftrace_location
> +static unsigned long klp_get_ftrace_location(unsigned long faddr)
> +{
> + return faddr;
> +}
> +#endif
Whoah, what an ugly hack :)
Note to my future self - This is what you want to do if you need a weak
static inline function.
static inline is probably unnecessary here so __weak function would be
enough. It would introduce powerpc-specific livepatch.c though because of
it and this is not worth it.
> static void klp_disable_func(struct klp_func *func)
> {
> struct klp_ops *ops;
> @@ -312,8 +325,14 @@ static void klp_disable_func(struct klp_func *func)
> return;
>
> if (list_is_singular(&ops->func_stack)) {
> + unsigned long ftrace_loc;
This is a nit, but could you move the definition up to have them all in
one place to be consistent with the rest of the code? The same applies to
klp_enable_func() below.
> +
> + ftrace_loc = klp_get_ftrace_location(func->old_addr);
> + if (WARN_ON(!ftrace_loc))
> + return;
> +
> WARN_ON(unregister_ftrace_function(&ops->fops));
> - WARN_ON(ftrace_set_filter_ip(&ops->fops, func->old_addr, 1, 0));
> + WARN_ON(ftrace_set_filter_ip(&ops->fops, ftrace_loc, 1, 0));
>
> list_del_rcu(&func->stack_node);
> list_del(&ops->node);
> @@ -338,6 +357,15 @@ static int klp_enable_func(struct klp_func *func)
>
> ops = klp_find_ops(func->old_addr);
> if (!ops) {
> + unsigned long ftrace_loc;
Here.
> +
> + ftrace_loc = klp_get_ftrace_location(func->old_addr);
> + if (!ftrace_loc) {
> + pr_err("failed to find location for function '%s'\n",
> + func->old_name);
> + return -EINVAL;
> + }
> +
> ops = kzalloc(sizeof(*ops), GFP_KERNEL);
> if (!ops)
> return -ENOMEM;
> @@ -352,7 +380,7 @@ static int klp_enable_func(struct klp_func *func)
> INIT_LIST_HEAD(&ops->func_stack);
> list_add_rcu(&func->stack_node, &ops->func_stack);
>
> - ret = ftrace_set_filter_ip(&ops->fops, func->old_addr, 0, 0);
> + ret = ftrace_set_filter_ip(&ops->fops, ftrace_loc, 0, 0);
> if (ret) {
> pr_err("failed to set ftrace filter for function '%s' (%d)\n",
> func->old_name, ret);
> @@ -363,7 +391,7 @@ static int klp_enable_func(struct klp_func *func)
> if (ret) {
> pr_err("failed to register ftrace handler for function '%s' (%d)\n",
> func->old_name, ret);
> - ftrace_set_filter_ip(&ops->fops, func->old_addr, 1, 0);
> + ftrace_set_filter_ip(&ops->fops, ftrace_loc, 1, 0);
> goto err;
> }
Otherwise it is ok.
Miroslav
next prev parent reply other threads:[~2016-04-14 12:01 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-13 12:53 [PATCH 0/5] Live patching for powerpc Michael Ellerman
2016-04-13 12:53 ` [PATCH 1/5] ftrace: Make ftrace_location_range() global Michael Ellerman
2016-04-19 10:16 ` [1/5] " Michael Ellerman
2016-04-13 12:53 ` [PATCH 2/5] livepatch: Allow architectures to specify an alternate ftrace location Michael Ellerman
2016-04-14 12:01 ` Miroslav Benes [this message]
2016-04-14 13:06 ` Michael Ellerman
2016-04-14 14:06 ` Miroslav Benes
2016-04-19 10:16 ` [2/5] " Michael Ellerman
2016-04-13 12:53 ` [PATCH 3/5] powerpc/livepatch: Add livepatch header Michael Ellerman
2016-04-14 12:18 ` Miroslav Benes
2016-04-14 12:23 ` Miroslav Benes
2016-04-14 13:12 ` Michael Ellerman
2016-04-19 10:16 ` [3/5] " Michael Ellerman
2016-04-13 12:53 ` [PATCH 4/5] powerpc/livepatch: Add livepatch stack to struct thread_info Michael Ellerman
2016-04-19 10:16 ` [4/5] " Michael Ellerman
2016-04-13 12:53 ` [PATCH 5/5] powerpc/livepatch: Add live patching support on ppc64le Michael Ellerman
2016-04-19 10:16 ` [5/5] " Michael Ellerman
2016-04-13 13:01 ` [PATCH 0/5] Live patching for powerpc Miroslav Benes
2016-04-13 13:22 ` Jiri Kosina
2016-04-14 6:49 ` Michael Ellerman
2016-04-14 12:57 ` Torsten Duwe
2016-04-14 13:08 ` Michael Ellerman
2016-04-14 15:20 ` Torsten Duwe
2016-04-14 16:41 ` Josh Poimboeuf
2016-04-15 11:22 ` Michael Ellerman
2016-04-15 12:59 ` Josh Poimboeuf
2016-04-15 13:21 ` Michael Ellerman
2016-04-14 14:34 ` Jiri Kosina
2016-04-15 12:24 ` Michael Ellerman
2016-04-15 15:07 ` Jiri Kosina
2016-04-19 21:42 ` Balbir Singh
2016-04-19 21:52 ` Jiri Kosina
2016-04-13 18:22 ` Jessica Yu
2016-04-14 13:28 ` Miroslav Benes
2016-04-14 19:20 ` Jessica Yu
2016-04-15 8:28 ` Miroslav Benes
2016-04-15 10:01 ` Michael Ellerman
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