Re: [Qemu-devel] [PATCH] Alpha bug fix: overflow condition for sublv and subqv

[Aurelien Jarno]

On Fri, Apr 10, 2009 at 10:55:20AM +0200, Tristan Gingold wrote:
> The conditions to detect overflow in sub operations was wrong.
> 
> This patch is necessary to boot Tru64.
> 
> Signed-off-by: Tristan Gingold <address@hidden>
> ---
>  target-alpha/op_helper.c |   20 ++++++++++----------
>  tests/alpha/Makefile     |    3 +++
>  tests/alpha/test-ovf.c   |   29 +++++++++++++++++++++++++++++
>  3 files changed, 42 insertions(+), 10 deletions(-)
>  create mode 100644 tests/alpha/test-ovf.c

Thanks, applied.

> diff --git a/target-alpha/op_helper.c b/target-alpha/op_helper.c
> index 7ad1b3d..3c95e98 100644
> --- a/target-alpha/op_helper.c
> +++ b/target-alpha/op_helper.c
> @@ -158,22 +158,22 @@ uint64_t helper_addlv (uint64_t op1, uint64_t op2)
>  
>  uint64_t helper_subqv (uint64_t op1, uint64_t op2)
>  {
> -    uint64_t tmp = op1;
> -    op1 -= op2;
> -    if (unlikely(((~tmp) ^ op1 ^ (-1ULL)) & ((~tmp) ^ op2) & (1ULL << 63))) {
> -        helper_excp(EXCP_ARITH, EXCP_ARITH_OVERFLOW);
> +    uint64_t res;
> +    res = op1 - op2;
> +    if (unlikely((op1 ^ op2) & (res ^ op1) & (1ULL << 63))) {
> +        helper_excp(EXCP_GEN_ARITH, EXCP_ARITH_OVERFLOW);
>      }
> -    return op1;
> +    return res;
>  }
>  
>  uint64_t helper_sublv (uint64_t op1, uint64_t op2)
>  {
> -    uint64_t tmp = op1;
> -    op1 = (uint32_t)(op1 - op2);
> -    if (unlikely(((~tmp) ^ op1 ^ (-1UL)) & ((~tmp) ^ op2) & (1UL << 31))) {
> -        helper_excp(EXCP_ARITH, EXCP_ARITH_OVERFLOW);
> +    uint32_t res;
> +    res = op1 - op2;
> +    if (unlikely((op1 ^ op2) & (res ^ op1) & (1UL << 31))) {
> +        helper_excp(EXCP_GEN_ARITH, EXCP_ARITH_OVERFLOW);
>      }
> -    return op1;
> +    return res;
>  }
>  
>  uint64_t helper_mullv (uint64_t op1, uint64_t op2)
> diff --git a/tests/alpha/Makefile b/tests/alpha/Makefile
> index e4e23d2..2b1f03d 100644
> --- a/tests/alpha/Makefile
> +++ b/tests/alpha/Makefile
> @@ -23,6 +23,9 @@ test-cmov.o: test-cond.c
>  test-cmov: test-cmov.o crt.o
>       $(LINK)
>  
> +test-ovf: test-ovf.o crt.o
> +     $(LINK)
> +
>  check: $(TESTS)
>       for f in $(TESTS); do $(SIM) $$f || exit 1; done
>  
> diff --git a/tests/alpha/test-ovf.c b/tests/alpha/test-ovf.c
> new file mode 100644
> index 0000000..01c80e7
> --- /dev/null
> +++ b/tests/alpha/test-ovf.c
> @@ -0,0 +1,29 @@
> +static long test_subqv (long a, long b)
> +{
> +  long res;
> +
> +  asm ("subq/v %1,%2,%0"
> +       : "=r" (res) : "r" (a), "r" (b));
> +  return res;
> +}
> +static struct {
> +  long (*func)(long, long);
> +  long a;
> +  long b;
> +  long r;
> +} vectors[] =
> +  {
> +    {test_subqv, 0, 0x7d54000, 0xfffffffff82ac000L}
> +  };
> +
> +int main (void)
> +{
> +  int i;
> +
> +  for (i = 0; i < sizeof (vectors)/sizeof(vectors[0]); i++)
> +    if ((*vectors[i].func)(vectors[i].a, vectors[i].b) != vectors[i].r) {
> +      write(1, "Failed\n", 7);
> +    }
> +  write(1, "OK\n", 3);
> +  return 0;
> +}
> -- 
> 1.6.2
> 
> 
> 
> 

-- 
Aurelien Jarno                          GPG: 1024D/F1BCDB73
address@hidden                 http://www.aurel32.net