(+ Nick)
On 7/2/19 6:49 pm, Segher Boessenkool wrote:
On Thu, Feb 07, 2019 at 05:59:48PM +1100, Andrew Donnellan wrote:
On 7/2/19 5:37 pm, Segher Boessenkool wrote:
On Thu, Feb 07, 2019 at 04:33:23PM +1100, Andrew Donnellan wrote:
Some older gccs (<GCC 7), when invoked with -fsanitize-coverage=trace-pc,
cause a spurious uninitialised variable warning in dt_cpu_ftrs.c:
arch/powerpc/kernel/dt_cpu_ftrs.c: In function
‘cpufeatures_process_feature’:
arch/powerpc/kernel/dt_cpu_ftrs.c:686:7: warning: ‘m’ may be used
uninitialized in this function [-Wmaybe-uninitialized]
if (m->cpu_ftr_bit_mask)
It seems to me the warning is correct? If enable_unknown is false and no
cpu_feature is found, it will in
if (m->cpu_ftr_bit_mask)
cur_cpu_spec->cpu_features |= m->cpu_ftr_bit_mask;
enable random features (whatever was last in the table), or indeed access
via NULL if the table is length 0? So maybe this should be
if (known && m->cpu_ftr_bit_mask)
cur_cpu_spec->cpu_features |= m->cpu_ftr_bit_mask;
instead? (The code would be much clearer if all the known vs. !known
codepath was fully separated here).
The table is never length 0, it's a statically defined array.
Sure, and presumably that is why newer GCC doesn't warn. But what about
the other point? Is this code ever correct? Enabling random features
(in cur_cpu_spec->cpu_features) when the name isn't found seems wrong.
Now that I'm replying without being 2 minutes before a meeting :)
The warning is still spurious, but the logic looks very suspicious.
I think your solution looks correct, though the whole function could be
cleaned up a bit.
I also notice that if enable_unknown == false, then I think an unknown
feature will still print "enabling" and return true, which seems wrong.
How does something like the following look, which I could send instead
and will probably solve the spurious warnings issues anyway?
diff --git a/arch/powerpc/kernel/dt_cpu_ftrs.c
b/arch/powerpc/kernel/dt_cpu_ftrs.c
index 2192b2114513..0f13048dc0dd 100644
--- a/arch/powerpc/kernel/dt_cpu_ftrs.c
+++ b/arch/powerpc/kernel/dt_cpu_ftrs.c
@@ -658,40 +658,31 @@ static void __init cpufeatures_setup_start(u32 isa)
static bool __init cpufeatures_process_feature(struct dt_cpu_feature *f)
{
- const struct dt_cpu_feature_match *m = NULL;
- bool known = false;
+ const struct dt_cpu_feature_match *m;
int i;
for (i = 0; i < ARRAY_SIZE(dt_cpu_feature_match_table); i++) {
m = &dt_cpu_feature_match_table[i];
if (!strcmp(f->name, m->name)) {
- known = true;
- if (m->enable(f))
- break;
-
- pr_info("not enabling: %s (disabled or
unsupported by kernel)\n",
- f->name);
- return false;
- }
- }
-
- if (!known && enable_unknown) {
- if (!feat_try_enable_unknown(f)) {
- pr_info("not enabling: %s (unknown and
unsupported by kernel)\n",
- f->name);
- return false;
+ if (!m->enable(f)) {
+ pr_info("not enabling: %s (disabled or
unsupported by kernel)\n",
+ f->name);
+ return false;
+ }
+ pr_debug("enabling: %s\n", f->name);
+ cur_cpu_spec->cpu_features |= m->cpu_ftr_bit_mask;
+ return true;
}
}
- if (m->cpu_ftr_bit_mask)
- cur_cpu_spec->cpu_features |= m->cpu_ftr_bit_mask;
-
- if (known)
- pr_debug("enabling: %s\n", f->name);
- else
+ if (enable_unknown && feat_try_enable_unknown(f)) {
pr_debug("enabling: %s (unknown)\n", f->name);
-
- return true;
+ return true;
+ } else {
+ pr_info("not enabling: %s (unknown and unsupported by
kernel)\n",
+ f->name);
+ return false;
+ }
}
static __init void cpufeatures_cpu_quirks(void)
--
Andrew Donnellan OzLabs, ADL Canberra
andrew.donnel...@au1.ibm.com IBM Australia Limited
