Re: [PATCH V4] livepatch: non static warnings fix

From: Joe Lawrence
Date: Thu Jan 24 2019 - 12:06:03 EST

On 1/23/19 8:48 PM, Nicholas Mc Guire wrote:
Sparse reported warnings about non-static symbols. For the variables
a simple static attribute is fine - for the functions referenced by
livepatch via klp_func the symbol-names must be unmodified in the
symbol table and the patchable code has to be emitted. The resolution
is to attach __used attribute to the shared statically declared functions.

Signed-off-by: Nicholas Mc Guire <hofrat@xxxxxxxxx>
Suggested-by: Joe Lawrence <joe.lawrence@xxxxxxxxxx>
Acked-by: Miroslav Benes <mbenes@xxxxxxx>
Link: https://lore.kernel.org/lkml/1544965657-26804-1-git-send-email-hofrat@xxxxxxxxx/

Hi Nicholas, thanks for re-posting this fix, the __used attribute change was particularly interesting to learn about.

I think Miroslav requested a re-ordering of these tags, perhaps we could do the shuffle when we apply the patch to the tree?

Link:
Suggested-by:
Signed-off-by:
Acked-by:

With that,

Acked-by: Joe Lawrence <joe.lawrence@xxxxxxxxxx>


---

V2: not all static functions shared need to carry the __noclone
attribute only those that need to be resolved at runtime by
livepatch - so drop the unnecessary __noclone attributes as
well as the Note on __noclone as suggested by Joe Lawrence
<joe.lawrence@xxxxxxxxxx> - thanks !

V3: fix the wording as proposed by Joe Lawrence
<joe.lawrence@xxxxxxxxxx> to address that this is not only
about how to fix sparse warnings but also to ensure
traceable/patchable code still being emitted.

V4: fix up the Link to point to the proper page as suggested
by Joe Lawrence <joe.lawrence@xxxxxxxxxx>.

Credit to Miroslav for these last two change suggestions.

-- Joe

Sparse reported the following findings in 5.0-rc3:

CHECK samples/livepatch/livepatch-shadow-mod.c
samples/livepatch/livepatch-shadow-mod.c:99:1: warning: symbol 'dummy_list' was not declared. Should it be static?
samples/livepatch/livepatch-shadow-mod.c:100:1: warning: symbol 'dummy_list_mutex' was not declared. Should it be static?
samples/livepatch/livepatch-shadow-mod.c:107:23: warning: symbol 'dummy_alloc' was not declared. Should it be static?
samples/livepatch/livepatch-shadow-mod.c:132:15: warning: symbol 'dummy_free' was not declared. Should it be static?
samples/livepatch/livepatch-shadow-mod.c:140:15: warning: symbol 'dummy_check' was not declared. Should it be static?

CHECK samples/livepatch/livepatch-shadow-fix1.c
samples/livepatch/livepatch-shadow-fix1.c:74:14: warning: symbol 'livepatch_fix1_dummy_alloc' was not declared. Should it be static?
samples/livepatch/livepatch-shadow-fix1.c:116:6: warning: symbol 'livepatch_fix1_dummy_free' was not declared. Should it be static?

CHECK samples/livepatch/livepatch-shadow-fix2.c
samples/livepatch/livepatch-shadow-fix2.c:53:6: warning: symbol 'livepatch_fix2_dummy_check' was not declared. Should it be static?
samples/livepatch/livepatch-shadow-fix2.c:81:6: warning: symbol 'livepatch_fix2_dummy_free' was not declared. Should it be static?

Patch was compile tested with: x86_64_defconfig + FTRACE=y
FUNCTION_TRACER=y, SAMPLES=y, LIVEPATCH=y SAMPLE_LIVEPATCH=m
(looks sparse, smatch claan, one coccichek warning left - fix later today)

Patch was runtested with:
insmod samples/livepatch/livepatch-shadow-mod.ko
insmod samples/livepatch/livepatch-shadow-fix1.ko
insmod samples/livepatch/livepatch-shadow-fix2.ko
echo 0 > /sys/kernel/livepatch/livepatch_shadow_fix2/enabled
echo 0 > /sys/kernel/livepatch/livepatch_shadow_fix1/enabled
rmmod livepatch-shadow-fix2
rmmod livepatch-shadow-fix1
rmmod livepatch-shadow-mod
and dmesg output compared to previous run.

Patch is against 5.0-rc3 (localversion-next is next-20190123)

samples/livepatch/livepatch-shadow-fix1.c | 4 ++--
samples/livepatch/livepatch-shadow-fix2.c | 4 ++--
samples/livepatch/livepatch-shadow-mod.c | 11 ++++++-----
3 files changed, 10 insertions(+), 9 deletions(-)

diff --git a/samples/livepatch/livepatch-shadow-fix1.c b/samples/livepatch/livepatch-shadow-fix1.c
index a5a5cac..67a73e5 100644
--- a/samples/livepatch/livepatch-shadow-fix1.c
+++ b/samples/livepatch/livepatch-shadow-fix1.c
@@ -71,7 +71,7 @@ static int shadow_leak_ctor(void *obj, void *shadow_data, void *ctor_data)
return 0;
}
-struct dummy *livepatch_fix1_dummy_alloc(void)
+static struct dummy *livepatch_fix1_dummy_alloc(void)
{
struct dummy *d;
void *leak;
@@ -113,7 +113,7 @@ static void livepatch_fix1_dummy_leak_dtor(void *obj, void *shadow_data)
__func__, d, *shadow_leak);
}
-void livepatch_fix1_dummy_free(struct dummy *d)
+static void livepatch_fix1_dummy_free(struct dummy *d)
{
void **shadow_leak;
diff --git a/samples/livepatch/livepatch-shadow-fix2.c b/samples/livepatch/livepatch-shadow-fix2.c
index 52de947..91c21d5 100644
--- a/samples/livepatch/livepatch-shadow-fix2.c
+++ b/samples/livepatch/livepatch-shadow-fix2.c
@@ -50,7 +50,7 @@ struct dummy {
unsigned long jiffies_expire;
};
-bool livepatch_fix2_dummy_check(struct dummy *d, unsigned long jiffies)
+static bool livepatch_fix2_dummy_check(struct dummy *d, unsigned long jiffies)
{
int *shadow_count;
@@ -78,7 +78,7 @@ static void livepatch_fix2_dummy_leak_dtor(void *obj, void *shadow_data)
__func__, d, *shadow_leak);
}
-void livepatch_fix2_dummy_free(struct dummy *d)
+static void livepatch_fix2_dummy_free(struct dummy *d)
{
void **shadow_leak;
int *shadow_count;
diff --git a/samples/livepatch/livepatch-shadow-mod.c b/samples/livepatch/livepatch-shadow-mod.c
index 4aa8a88..4d79c6dc 100644
--- a/samples/livepatch/livepatch-shadow-mod.c
+++ b/samples/livepatch/livepatch-shadow-mod.c
@@ -96,15 +96,15 @@ MODULE_DESCRIPTION("Buggy module for shadow variable demo");
* Keep a list of all the dummies so we can clean up any residual ones
* on module exit
*/
-LIST_HEAD(dummy_list);
-DEFINE_MUTEX(dummy_list_mutex);
+static LIST_HEAD(dummy_list);
+static DEFINE_MUTEX(dummy_list_mutex);
struct dummy {
struct list_head list;
unsigned long jiffies_expire;
};
-noinline struct dummy *dummy_alloc(void)
+static __used noinline struct dummy *dummy_alloc(void)
{
struct dummy *d;
void *leak;
@@ -129,7 +129,7 @@ noinline struct dummy *dummy_alloc(void)
return d;
}
-noinline void dummy_free(struct dummy *d)
+static __used noinline void dummy_free(struct dummy *d)
{
pr_info("%s: dummy @ %p, expired = %lx\n",
__func__, d, d->jiffies_expire);
@@ -137,7 +137,8 @@ noinline void dummy_free(struct dummy *d)
kfree(d);
}
-noinline bool dummy_check(struct dummy *d, unsigned long jiffies)
+static __used noinline bool dummy_check(struct dummy *d,
+ unsigned long jiffies)
{
return time_after(jiffies, d->jiffies_expire);
}