[Qemu-devel] [PATCH] target-arm: fix sdiv helper

[Qemu-devel] [PATCH] target-arm: fix sdiv helper

[Aurelien Jarno]

(INT32_MIN / -1) triggers an overflow, and the result depends on the
host architecture (INT32_MIN on arm, -1 on ppc, SIGFPE on x86). Use a
test to output the correct value.

Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
---
 target-arm/helper.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/target-arm/helper.c b/target-arm/helper.c
index 701629a..b3d6198 100644
--- a/target-arm/helper.c
+++ b/target-arm/helper.c
@@ -404,6 +404,8 @@ int32_t HELPER(sdiv)(int32_t num, int32_t den)
 {
     if (den == 0)
       return 0;
+    if (num == INT_MIN && den == -1)
+      return INT_MIN;
     return num / den;
 }
 
-- 
1.6.1.3

Re: [Qemu-devel] [PATCH] target-arm: fix sdiv helper

[Laurent Desnogues]

On Thu, Oct 15, 2009 at 11:08 PM, Aurelien Jarno <aurelien@aurel32.net> wrote:
> (INT32_MIN / -1) triggers an overflow, and the result depends on the
> host architecture (INT32_MIN on arm, -1 on ppc, SIGFPE on x86). Use a
> test to output the correct value.
>
> Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
> ---
>  target-arm/helper.c |    2 ++
>  1 files changed, 2 insertions(+), 0 deletions(-)
>
> diff --git a/target-arm/helper.c b/target-arm/helper.c
> index 701629a..b3d6198 100644
> --- a/target-arm/helper.c
> +++ b/target-arm/helper.c
> @@ -404,6 +404,8 @@ int32_t HELPER(sdiv)(int32_t num, int32_t den)
>  {
>     if (den == 0)
>       return 0;
> +    if (num == INT_MIN && den == -1)
> +      return INT_MIN;
>     return num / den;
>  }
>
> --
> 1.6.1.3

Acked-by: Laurent Desnogues <laurent.desnogues@gmail.com>

That is provided we accept the behaviour for division by zero is
not strictly conforming to what the ARM ARM says.

Also note this instruction is not available on v7-A CPU's (Cortex-A8
for instance).  It's part of v7-R (Cortex R4).


Laurent