[Qemu-devel] [PATCH v2] sparc32 : Signed integer division overflow

[Qemu-devel] [PATCH v2] sparc32 : Signed integer division overflow

[Olivier Danet]

The signed integer division -0x8000_0000_0000_0000 / -1 must be handled
separately to avoid an overflow on the QEMU host.

Signed-off-by: Olivier Danet <odanet@caramail.com>
---
 target-sparc/helper.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/target-sparc/helper.c b/target-sparc/helper.c
index f3c7fbf..3822c48 100644
--- a/target-sparc/helper.c
+++ b/target-sparc/helper.c
@@ -122,12 +122,15 @@ static target_ulong helper_sdiv_common(CPUSPARCState *env, target_ulong a,
     if (x1 == 0) {
         cpu_restore_state(CPU(cpu), GETPC());
         helper_raise_exception(env, TT_DIV_ZERO);
-    }
-
-    x0 = x0 / x1;
-    if ((int32_t) x0 != x0) {
-        x0 = x0 < 0 ? 0x80000000 : 0x7fffffff;
+    } else if (x1 == -1 && x0 == INT64_MIN) {
+        x0 = 0x7fffffff;
         overflow = 1;
+    } else {
+        x0 = x0 / x1;
+        if ((int32_t) x0 != x0) {
+            x0 = x0 < 0 ? 0x80000000 : 0x7fffffff;
+            overflow = 1;
+        }
     }
 
     if (cc) {
-- 
1.8.1.5

Re: [Qemu-devel] [PATCH v2] sparc32 : Signed integer division overflow

[Richard Henderson]

On 03/19/2014 03:29 PM, Olivier Danet wrote:
> The signed integer division -0x8000_0000_0000_0000 / -1 must be handled
> separately to avoid an overflow on the QEMU host.
> 
> Signed-off-by: Olivier Danet <odanet@caramail.com>
> ---
>  target-sparc/helper.c | 13 ++++++++-----
>  1 file changed, 8 insertions(+), 5 deletions(-)

Reviewed-by: Richard Henderson <rth@twiddle.net>


r~

Re: [Qemu-devel] [PATCH v2] sparc32 : Signed integer division overflow

[Richard Henderson]

On 03/19/2014 03:29 PM, Olivier Danet wrote:
> +        if ((int32_t) x0 != x0) {
> +            x0 = x0 < 0 ? 0x80000000 : 0x7fffffff;
> +            overflow = 1;
> +        }

Actually, there's an existing bug here that we might as well fix.

  ## ... the 32-bit result is sign-extended to 64 bits and
  ## written into register R[rd].

That 0x80000000 is not going to promote properly to 64-bits.  We might as well
go ahead and use INT32_MIN and INT32_MAX here at the same time.



r~