The migration stream lacks magic numbers at some key points. It's easy
to mis-parse data. Unfortunately, the VMS_NULLPTR_MARKER continues
with the trend. A '0' byte is ambiguous and could be interpreted as a
valid 0x30.
It is maybe not worth trying to change this while keeping backward
compatibility, so add some words of documentation to clarify.
Signed-off-by: Fabiano Rosas <faro...@suse.de>
---
migration/vmstate-types.c | 6 ++++++
scripts/analyze-migration.py | 9 +++++++++
2 files changed, 15 insertions(+)
diff --git a/migration/vmstate-types.c b/migration/vmstate-types.c
index e83bfccb9e..08ed059f87 100644
--- a/migration/vmstate-types.c
+++ b/migration/vmstate-types.c
@@ -339,6 +339,12 @@ static int put_nullptr(QEMUFile *f, void *pv, size_t size,
const VMStateInfo vmstate_info_nullptr = {
.name = "uint64",
+
+ /*
+ * Ideally these would actually read/write the size of a pointer,
+ * but we're stuck with just a byte now for backward
+ * compatibility.
+ */
.get = get_nullptr,
.put = put_nullptr,
};
diff --git a/scripts/analyze-migration.py b/scripts/analyze-migration.py
index f2457b1dde..4292fde424 100755
--- a/scripts/analyze-migration.py
+++ b/scripts/analyze-migration.py
@@ -388,12 +388,21 @@ def read(self):
return self.data
class VMSDFieldUInt(VMSDFieldInt):
+ NULL_PTR_MARKER = 0x30
+
def __init__(self, desc, file):
super(VMSDFieldUInt, self).__init__(desc, file)
def read(self):
super(VMSDFieldUInt, self).read()
self.data = self.udata
+
+ if self.data == self.NULL_PTR_MARKER:
+ # The migration stream encodes NULL pointers as '0' so any
+ # 0x30 in the stream could be a NULL. There's not much we
+ # can do without breaking backward compatibility.
+ pass
+
return self.data
class VMSDFieldIntLE(VMSDFieldInt):
--
2.35.3
