Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Mon,  5 Dec 2022 15:57:40 +0100
In-Reply-To: <20221205132558.63484-1-glider@google.com>
Mime-Version: 1.0
References: <20221205132558.63484-1-glider@google.com>
Message-ID: <20221205145740.694038-1-glider@google.com>
Subject: [PATCH v2] kmsan: fix memcpy tests
From:   Alexander Potapenko <glider@google.com>
To:     glider@google.com
Cc:     linux-kernel@vger.kernel.org, akpm@linux-foundation.org,
        elver@google.com, dvyukov@google.com, linux-mm@kvack.org
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

Recent Clang changes may cause it to delete calls of memcpy(), if the
source is an uninitialized volatile local.
This happens because passing a pointer to a volatile local into memcpy()
discards the volatile qualifier, giving the compiler a free hand to
optimize the memcpy() call away.

Use OPTIMIZER_HIDE_VAR() to hide the uninitialized var from the
too-smart compiler.

Suggested-by: Marco Elver <elver@google.com>
Signed-off-by: Alexander Potapenko <glider@google.com>
---
 mm/kmsan/kmsan_test.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/kmsan/kmsan_test.c b/mm/kmsan/kmsan_test.c
index 9a29ea2dbfb9b..eb44ef3c5f290 100644
--- a/mm/kmsan/kmsan_test.c
+++ b/mm/kmsan/kmsan_test.c
@@ -419,6 +419,7 @@ static void test_memcpy_aligned_to_aligned(struct kunit *test)
 	kunit_info(
 		test,
 		"memcpy()ing aligned uninit src to aligned dst (UMR report)\n");
+	OPTIMIZER_HIDE_VAR(uninit_src);
 	memcpy((void *)&dst, (void *)&uninit_src, sizeof(uninit_src));
 	kmsan_check_memory((void *)&dst, sizeof(dst));
 	KUNIT_EXPECT_TRUE(test, report_matches(&expect));
@@ -441,6 +442,7 @@ static void test_memcpy_aligned_to_unaligned(struct kunit *test)
 	kunit_info(
 		test,
 		"memcpy()ing aligned uninit src to unaligned dst (UMR report)\n");
+	OPTIMIZER_HIDE_VAR(uninit_src);
 	memcpy((void *)&dst[1], (void *)&uninit_src, sizeof(uninit_src));
 	kmsan_check_memory((void *)dst, 4);
 	KUNIT_EXPECT_TRUE(test, report_matches(&expect));
@@ -464,6 +466,7 @@ static void test_memcpy_aligned_to_unaligned2(struct kunit *test)
 	kunit_info(
 		test,
 		"memcpy()ing aligned uninit src to unaligned dst - part 2 (UMR report)\n");
+	OPTIMIZER_HIDE_VAR(uninit_src);
 	memcpy((void *)&dst[1], (void *)&uninit_src, sizeof(uninit_src));
 	kmsan_check_memory((void *)&dst[4], sizeof(uninit_src));
 	KUNIT_EXPECT_TRUE(test, report_matches(&expect));
-- 
2.39.0.rc0.267.gcb52ba06e7-goog