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Re: [Qemu-ppc] [RFC] spapr_drc: Fix potential undefined behaviour


From: Alexey Kardashevskiy
Subject: Re: [Qemu-ppc] [RFC] spapr_drc: Fix potential undefined behaviour
Date: Wed, 2 Sep 2015 18:21:34 +1000
User-agent: Mozilla/5.0 (X11; Linux i686 on x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.2.0

On 09/01/2015 01:17 PM, David Gibson wrote:
The DRC_INDEX_ID_MASK macro does a left shift on ~0, which is a signed
quantity, and therefore undefined behaviour according to the C spec.  In
particular this causes warnings from the clang sanitizer.

This fixes it by calculating the same mask without using ~0 (I think the
new method is a more common idiom for generating masks anyway).  For good
measure I also use 1ULL to force the expression's type to unsigned long
long, which should be good for assigning to anything we're going to want
to.

Reported-by: Peter Maydell <address@hidden>
Signed-off-by: David Gibson <address@hidden>

Reviewed-by: Alexey Kardashevskiy <address@hidden>        

---
  hw/ppc/spapr_drc.c | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

I'm hoping to get some Reviewed-bys for this patch so that I'm ready
to merge my spapr-next queue.

diff --git a/hw/ppc/spapr_drc.c b/hw/ppc/spapr_drc.c
index ee87432..8cbcf4d 100644
--- a/hw/ppc/spapr_drc.c
+++ b/hw/ppc/spapr_drc.c
@@ -32,7 +32,7 @@

  #define DRC_CONTAINER_PATH "/dr-connector"
  #define DRC_INDEX_TYPE_SHIFT 28
-#define DRC_INDEX_ID_MASK (~(~0 << DRC_INDEX_TYPE_SHIFT))
+#define DRC_INDEX_ID_MASK ((1ULL << DRC_INDEX_TYPE_SHIFT) - 1)

  static sPAPRDRConnectorTypeShift get_type_shift(sPAPRDRConnectorType type)
  {



--
Alexey



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