Subject: Re: [PATCH v14 8/8] lib/tests: memcpy_kunit: add memcpy_mc() and memcpy_mc_large() test

From: Shuai Xue <[email-masked]>
Date: Thu, 28 May 2026 11:17:17 +0800

On 5/18/26 4:49 PM, Ruidong Tian wrote:
> memcpy_mc() is the Machine-Check safe memcpy variant that returns the
> number of bytes NOT copied on a hardware memory error, or 0 on success.
> 
> Add two test cases modeled after the existing memcpy_test() and
> memcpy_large_test() implementations:

Same build issue as with copy_mc_page_test: memcpy_mc() is an arm64-
only symbol.

1. Cross-architecture build break (BLOCKER, same as patch 6)

    These tests are gated on CONFIG_ARCH_HAS_COPY_MC, which is also
    selected by x86_64 and ppc64. Neither architecture provides a
    memcpy_mc() symbol -- they use copy_mc_to_kernel() directly.

    On x86_64:

        lib/tests/memcpy_kunit.c: error: implicit declaration of
        function 'memcpy_mc' [-Werror=implicit-function-declaration]

    Fix: guard with __HAVE_ARCH_MEMCPY_MC instead:

        #ifdef __HAVE_ARCH_MEMCPY_MC
        static void memcpy_mc_test(...) { ... }
        static void memcpy_mc_large_test(...) { ... }
        #endif

> 
> Signed-off-by: Ruidong Tian <[email-masked]>
> ---
>   lib/tests/memcpy_kunit.c | 113 ++++++++++++++++++++++++++++++++++++++-
>   1 file changed, 112 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/tests/memcpy_kunit.c b/lib/tests/memcpy_kunit.c
> index 85df53ccfb0c..b4b2dafb50f1 100644
> --- a/lib/tests/memcpy_kunit.c
> +++ b/lib/tests/memcpy_kunit.c
> @@ -552,6 +552,115 @@ static void copy_mc_page_test(struct kunit *test)
>   		memcmp(page_dst + PAGE_SIZE, page_zero, PAGE_SIZE), 0,
>   		"copy_mc_page overflow into adjacent page");
>   }
> +/*
> + * memcpy_mc() is a Machine-Check safe memcpy variant.
> + * Signature: int memcpy_mc(void *dst, const void *src, size_t len)
> + * Returns:   0 on success, or number of bytes NOT copied on MC error.
> + *
> + * In the normal (no-poison) path it must behave identically to memcpy()
> + * and always return 0.
> + */
> +static void memcpy_mc_test(struct kunit *test)
> +{
> +#define TEST_OP "memcpy_mc"
> +	struct some_bytes control = {
> +		.data = { 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
> +			  0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
> +			  0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
> +			  0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
> +		},
> +	};
> +	struct some_bytes zero = { };
> +	struct some_bytes middle = {
> +		.data = { 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
> +			  0x20, 0x20, 0x20, 0x20, 0x00, 0x00, 0x00, 0x00,
> +			  0x00, 0x00, 0x00, 0x20, 0x20, 0x20, 0x20, 0x20,
> +			  0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
> +		},
> +	};
> +	struct some_bytes three = {
> +		.data = { 0x00, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
> +			  0x20, 0x00, 0x00, 0x20, 0x20, 0x20, 0x20, 0x20,
> +			  0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
> +			  0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20, 0x20,
> +			},
> +	};
> +	struct some_bytes dest = { };
> +	int ret, count;
> +	u8 *ptr;
> +
> +	/* Verify static initializers. */
> +	check(control, 0x20);
> +	check(zero, 0);
> +	compare("static initializers", dest, zero);
> +
> +	/* Verify assignment. */
> +	dest = control;
> +	compare("direct assignment", dest, control);
> +
> +	/* Verify complete overwrite. */
> +	ret = memcpy_mc(dest.data, control.data, sizeof(dest.data));
> +	KUNIT_ASSERT_EQ(test, ret, 0);
> +	compare("complete overwrite", dest, control);
> +
> +	/* Verify middle overwrite: 7 bytes at offset 12. */
> +	dest = control;
> +	ret = memcpy_mc(dest.data + 12, zero.data, 7);
> +	KUNIT_ASSERT_EQ(test, ret, 0);
> +	compare("middle overwrite", dest, middle);
> +
> +	/* Verify zero-length copy is a no-op. */
> +	dest = control;
> +	ret = memcpy_mc(dest.data, zero.data, 0);
> +	KUNIT_ASSERT_EQ(test, ret, 0);
> +	compare("zero length", dest, control);
> +
> +	/* Verify argument side-effects aren't repeated. */
> +	dest = control;
> +	ptr = dest.data;
> +	count = 1;
> +	memcpy(ptr++, zero.data, count++);
> +	ptr += 8;
> +	memcpy(ptr++, zero.data, count++);

    This is a verbatim paste from memcpy_test(). The intent is to
    verify that the memcpy_mc macro doesn't double-evaluate arguments,
    but the test doesn't actually call memcpy_mc(). Please change the
    two memcpy() calls to memcpy_mc() and assert their return values.

Thanks
Shuai