Re: [qemu-s390x] [PATCH 6/7] target/s390x: fix PACK reading 1 byte less and writing 1 byte more

[David Hildenbrand]

On 21.08.2018 04:51, Pavel Zbitskiy wrote:
> PACK fails on the test from the Principles of Operation: F1F2F3F4
> becomes 0000234C instead of 0001234C due to an off-by-one error.
> Furthermore, it overwrites one extra byte to the left of F1.
> 
> If len_dest is 0, then we only want to flip the 1st byte and never loop
> over the rest. Therefore, the loop condition should be > and not >=.
> 
> If len_src is 1, then we should flip the 1st byte and pack the 2nd.
> Since len_src is already decremented before the loop, the first
> condition should be >=, and not >.
> 
> Likewise for len_src == 2 and the second condition.
> 
> Signed-off-by: Pavel Zbitskiy <address@hidden>
> ---
>  target/s390x/mem_helper.c       |  6 +++---
>  tests/tcg/s390x/Makefile.target |  1 +
>  tests/tcg/s390x/pack.c          | 21 +++++++++++++++++++++
>  3 files changed, 25 insertions(+), 3 deletions(-)
>  create mode 100644 tests/tcg/s390x/pack.c
> 
> diff --git a/target/s390x/mem_helper.c b/target/s390x/mem_helper.c
> index 704d0193b5..bacae4f503 100644
> --- a/target/s390x/mem_helper.c
> +++ b/target/s390x/mem_helper.c
> @@ -1019,15 +1019,15 @@ void HELPER(pack)(CPUS390XState *env, uint32_t len, 
> uint64_t dest, uint64_t src)
>      len_src--;
>  
>      /* now pack every value */
> -    while (len_dest >= 0) {
> +    while (len_dest > 0) {
>          b = 0;
>  
> -        if (len_src > 0) {
> +        if (len_src >= 0) {
>              b = cpu_ldub_data_ra(env, src, ra) & 0x0f;
>              src--;
>              len_src--;
>          }
> -        if (len_src > 0) {
> +        if (len_src >= 0) {
>              b |= cpu_ldub_data_ra(env, src, ra) << 4;
>              src--;
>              len_src--;
> diff --git a/tests/tcg/s390x/Makefile.target b/tests/tcg/s390x/Makefile.target
> index 7de4376f52..151dc075aa 100644
> --- a/tests/tcg/s390x/Makefile.target
> +++ b/tests/tcg/s390x/Makefile.target
> @@ -5,3 +5,4 @@ TESTS+=csst
>  TESTS+=ipm
>  TESTS+=exrl-trt
>  TESTS+=exrl-trtr
> +TESTS+=pack
> diff --git a/tests/tcg/s390x/pack.c b/tests/tcg/s390x/pack.c
> new file mode 100644
> index 0000000000..4be36f29a7
> --- /dev/null
> +++ b/tests/tcg/s390x/pack.c
> @@ -0,0 +1,21 @@
> +#include <unistd.h>
> +
> +int main(void)
> +{
> +    char data[] = {0xaa, 0xaa, 0xf1, 0xf2, 0xf3, 0xc4, 0xaa, 0xaa};
> +    char exp[] = {0xaa, 0xaa, 0x00, 0x01, 0x23, 0x4c, 0xaa, 0xaa};
> +    int i;
> +
> +    asm volatile(
> +        "    pack 2(4,%[data]),2(4,%[data])\n"
> +        :
> +        : [data] "r" (&data[0])
> +        : "memory");
> +    for (i = 0; i < 8; i++) {
> +        if (data[i] != exp[i]) {
> +            write(1, "bad data\n", 9);
> +            return 1;
> +        }
> +    }
> +    return 0;
> +}
> 
Reviewed-by: David Hildenbrand <address@hidden>

-- 

Thanks,

David / dhildenb