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From: | Mark Cave-Ayland |
Subject: | Re: [Qemu-devel] [PATCH] sparc32 : Signed integer division overflow |
Date: | Tue, 18 Mar 2014 00:20:55 +0000 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:10.0.12) Gecko/20130116 Icedove/10.0.12 |
On 12/03/14 21:26, Olivier Danet wrote: Hi Olivier,
Here is a patch for handling this corner case on SPARC32. SPARC64 division already checks this in helper_sdivx(), some other architectures seem to do the same (for example, target-arm/helper.c: HELPER(sdiv)) =================================================================== The integer division 0x8000_0000_0000_0000 / -1 must be handled separately to avoid overflows on the QEMU host. Signed-off-by: Olivier Danet <address@hidden> ------------------------------------------------------------------- diff --git a/target-sparc/helper.c b/target-sparc/helper.c index 57c20af..b6b5937 100644 --- a/target-sparc/helper.c +++ b/target-sparc/helper.c @@ -116,14 +116,16 @@ static target_ulong helper_sdiv_common(CPUSPARCState *env, target_ulong a, if (x1 == 0) { cpu_restore_state(env, 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 == 0x8000000000000000) { + x0 = 0x7fffffff; overflow = 1;
Thanks for the patch! I think based upon Peter's recent series that the sign constant would need a ULL suffix in order to function correctly on 32-bit platforms.
My personal preference would be for (1ULL << 63) unless Peter (CC added) can think of a reason to leave the hex constant in its current form?
That said, I've tested the patch on a Debian etch Linux image and it works for me.
+ } else { + x0 = x0 / x1; + if ((int32_t) x0 != x0) { + x0 = x0 < 0 ? 0x80000000 : 0x7fffffff; + overflow = 1; + } } -
Looks like a whitespace change accidentally made it into this patch too.
if (cc) { env->cc_dst = x0; env->cc_src2 = overflow; -------------------------------------------------------------------
ATB, Mark.
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