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migration/vmstate: fix array of ptr with nullptrs

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Make VMS_ARRAY_OF_POINTER cope with null pointers. Previously the
reward for trying to migrate an array with some null pointers in it was
an illegal memory access, that is a swift and painless death of the
process.  Let's make vmstate cope with this scenario.

The general approach is, when we encounter a null pointer (element),
instead of following the pointer to save/load the data behind it, we
save/load a placeholder. This way we can detect if we expected a null
pointer at the load side but not null data was saved instead.

Signed-off-by: Halil Pasic <pasic@linux.vnet.ibm.com>
Reviewed-by: Guenther Hutzl <hutzl@linux.vnet.ibm.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-Id: <20170222160119.52771-4-pasic@linux.vnet.ibm.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
This commit is contained in:
Halil Pasic 2017-02-22 17:01:17 +01:00 • committed by Dr. David Alan Gilbert
parent cbfda0e6cf
commit 07d4e69147
2 changed files with 42 additions and 2 deletions
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4
include/migration/vmstate.h
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@ -253,6 +253,10 @@ extern const VMStateInfo vmstate_info_uint16;
extern const VMStateInfo vmstate_info_uint32;
extern const VMStateInfo vmstate_info_uint64;
/** Put this in the stream when migrating a null pointer.*/
#define VMS_NULLPTR_MARKER (0x30U) /* '0' */
extern const VMStateInfo vmstate_info_nullptr;
extern const VMStateInfo vmstate_info_float64;
extern const VMStateInfo vmstate_info_cpudouble;