Re: [PATCH] tests/tcg/s390x: Add cdsg.c

[David Hildenbrand <david@redhat.com>]

On 29.11.22 00:48, Ilya Leoshkevich wrote:
> Add a simple test to prevent regressions.
> 
> Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
> ---
>   tests/tcg/s390x/Makefile.target |  4 ++
>   tests/tcg/s390x/cdsg.c          | 73 +++++++++++++++++++++++++++++++++
>   2 files changed, 77 insertions(+)
>   create mode 100644 tests/tcg/s390x/cdsg.c
> 
> diff --git a/tests/tcg/s390x/Makefile.target b/tests/tcg/s390x/Makefile.target
> index 1d454270c0e..523214dac33 100644
> --- a/tests/tcg/s390x/Makefile.target
> +++ b/tests/tcg/s390x/Makefile.target
> @@ -27,6 +27,7 @@ TESTS+=noexec
>   TESTS+=div
>   TESTS+=clst
>   TESTS+=long-double
> +TESTS+=cdsg
>   
>   Z13_TESTS=vistr
>   $(Z13_TESTS): CFLAGS+=-march=z13 -O2
> @@ -66,3 +67,6 @@ sha512-mvx: sha512.c
>   	$(CC) $(CFLAGS) $(EXTRA_CFLAGS) $< -o $@ $(LDFLAGS)
>   
>   TESTS+=sha512-mvx
> +
> +cdsg: CFLAGS+=-pthread
> +cdsg: LDFLAGS+=-pthread
> diff --git a/tests/tcg/s390x/cdsg.c b/tests/tcg/s390x/cdsg.c
> new file mode 100644
> index 00000000000..83313699f7d
> --- /dev/null
> +++ b/tests/tcg/s390x/cdsg.c
> @@ -0,0 +1,73 @@
> +#include <assert.h>
> +#include <pthread.h>
> +#include <stdbool.h>
> +#include <stdlib.h>
> +
> +static volatile bool start;
> +static unsigned long val[2] __attribute__((__aligned__(16)));
> +
> +void *cdsg_loop(void *arg)
> +{
> +    unsigned long orig0, orig1, new0, new1;
> +    register unsigned long r0 asm("r0");
> +    register unsigned long r1 asm("r1");
> +    register unsigned long r2 asm("r2");
> +    register unsigned long r3 asm("r3");
> +    int cc;
> +    int i;
> +
> +    while (!start) {
> +    }
> +
> +    orig0 = val[0];
> +    orig1 = val[1];
> +    for (i = 0; i < 1000;) {

Are 1000 iterations sufficient to catch the race window reliably?

> +        new0 = orig0 + 1;
> +        new1 = orig1 + 2;
> +
> +        r0 = orig0;
> +        r1 = orig1;
> +        r2 = new0;
> +        r3 = new1;
> +        asm("cdsg %[r0],%[r2],%[db2]\n"
> +            "ipm %[cc]"
> +            : [r0] "+r" (r0)
> +            , [r1] "+r" (r1)
> +            , [db2] "=m" (val)
> +            , [cc] "=r" (cc)
> +            : [r2] "r" (r2)
> +            , [r3] "r" (r3)
> +            : "cc");

Nit: I'd suggest a simple cdsg helper function that makes this code 
easier to digest.

> +        orig0 = r0;
> +        orig1 = r1;
> +        cc = (cc >> 28) & 3;
> +
> +        if (cc == 0) {
> +            orig0 = new0;
> +            orig1 = new1;
> +            i++;
> +        } else {
> +            assert(cc == 1);
> +        }
> +    }
> +
> +    return NULL;
> +}
> +
> +int main(void)
> +{
> +    pthread_t thread;
> +    int ret;
> +
> +    ret = pthread_create(&thread, NULL, cdsg_loop, NULL);
> +    assert(ret == 0);
> +    start = true;
> +    cdsg_loop(NULL);
> +    ret = pthread_join(thread, NULL);
> +    assert(ret == 0);
> +
> +    assert(val[0] == 2000);
> +    assert(val[1] == 4000);
> +
> +    return EXIT_SUCCESS;
> +}

-- 
Thanks,

David / dhildenb