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* [PATCH v2 1/2] powerpc/64s: Fix logic when handling unknown CPU features
@ 2019-02-11  0:20 Andrew Donnellan
  2019-02-11  0:20 ` [PATCH v2 2/2] powerpc: Enable kcov Andrew Donnellan
  2019-02-22  9:47 ` [v2, 1/2] powerpc/64s: Fix logic when handling unknown CPU features Michael Ellerman
  0 siblings, 2 replies; 5+ messages in thread
From: Andrew Donnellan @ 2019-02-11  0:20 UTC (permalink / raw)
  To: linuxppc-dev; +Cc: syzkaller, npiggin, dvyukov

From: Michael Ellerman <mpe@ellerman.id.au>

In cpufeatures_process_feature(), if a provided CPU feature is unknown and
enable_unknown is false, we erroneously print that the feature is being
enabled and return true, even though no feature has been enabled, and
may also set feature bits based on the last entry in the match table.

Fix this so that we only set feature bits from the match table if we have
actually enabled a feature from that table, and when failing to enable an
unknown feature, always print the "not enabling" message and return false.

Coincidentally, some older gccs (<GCC 7), when invoked with
-fsanitize-coverage=trace-pc, cause a spurious uninitialised variable
warning in this function:

  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)

An upcoming patch will enable support for kcov, which requires this option.
This patch avoids the warning.

Fixes: 5a61ef74f269 ("powerpc/64s: Support new device tree binding for discovering CPU features")
Reported-by: Segher Boessenkool <segher@kernel.crashing.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
[ajd: add commit message]
Signed-off-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>

---
v1->v2:
- fix the other logic errors in this function (segher, mpe)

---
 arch/powerpc/kernel/dt_cpu_ftrs.c | 17 +++++++----------
 1 file changed, 7 insertions(+), 10 deletions(-)

diff --git a/arch/powerpc/kernel/dt_cpu_ftrs.c b/arch/powerpc/kernel/dt_cpu_ftrs.c
index 8be3721d9302..e49bd5efcfe6 100644
--- a/arch/powerpc/kernel/dt_cpu_ftrs.c
+++ b/arch/powerpc/kernel/dt_cpu_ftrs.c
@@ -666,8 +666,10 @@ static bool __init cpufeatures_process_feature(struct dt_cpu_feature *f)
 		m = &dt_cpu_feature_match_table[i];
 		if (!strcmp(f->name, m->name)) {
 			known = true;
-			if (m->enable(f))
+			if (m->enable(f)) {
+				cur_cpu_spec->cpu_features |= m->cpu_ftr_bit_mask;
 				break;
+			}
 
 			pr_info("not enabling: %s (disabled or unsupported by kernel)\n",
 				f->name);
@@ -675,17 +677,12 @@ static bool __init cpufeatures_process_feature(struct dt_cpu_feature *f)
 		}
 	}
 
-	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 (!known && (!enable_unknown || !feat_try_enable_unknown(f))) {
+		pr_info("not enabling: %s (unknown and unsupported by kernel)\n",
+			f->name);
+		return false;
 	}
 
-	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
-- 
2.11.0


^ permalink raw reply related	[flat|nested] 5+ messages in thread
end of thread, other threads:[~2019-02-22 10:21 UTC | newest]

Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-02-11  0:20 [PATCH v2 1/2] powerpc/64s: Fix logic when handling unknown CPU features Andrew Donnellan
2019-02-11  0:20 ` [PATCH v2 2/2] powerpc: Enable kcov Andrew Donnellan
2019-02-20  4:26   ` Daniel Axtens
2019-02-20  4:47     ` Andrew Donnellan
2019-02-22  9:47 ` [v2, 1/2] powerpc/64s: Fix logic when handling unknown CPU features Michael Ellerman

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