Re: [Qemu-devel] [PATCH] scripts/dump-guest-memory.py: fix int128_get64 on recent gcc

[Marc-André Lureau]

Hi

On Fri, Mar 10, 2017 at 2:00 PM Paolo Bonzini <address@hidden> wrote:

>
>
> On 10/03/2017 09:53, Marc-André Lureau wrote:
> > The Int128 is no longer a struct, reaching a python exception:
> > Python Exception <class 'gdb.error'> Attempt to extract a component of a
> value that is not a (null).:
> >
> > Replace struct access with a cast to uint64 instead.
> >
> > Fixes:
> > https://bugzilla.redhat.com/show_bug.cgi?id=1427466
> >
> > Signed-off-by: Marc-André Lureau <address@hidden>
> > ---
> >  scripts/dump-guest-memory.py | 6 ++++--
> >  1 file changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/scripts/dump-guest-memory.py b/scripts/dump-guest-memory.py
> > index 9956fc036c..bbe1c14ba2 100644
> > --- a/scripts/dump-guest-memory.py
> > +++ b/scripts/dump-guest-memory.py
> > @@ -314,8 +314,10 @@ def get_arch_phdr(endianness, elfclass):
> >  def int128_get64(val):
> >      """Returns low 64bit part of Int128 struct."""
> >
> > -    assert val["hi"] == 0
> > -    return val["lo"]
> > +    u64t = gdb.lookup_type('uint64_t').array(2)
> > +    u64 = val.cast(u64t)
> > +    assert u64[1] == 0
> > +    return u64[0]
> >
> >
> >  def qlist_foreach(head, field_str):
> >
>
> I'm afraid this is not big-endian-friendly (Python lets you check that
> with "sys.byteorder == 'little'").
>
> Also when building on a 32-bit machine the old code should be used; I
> think you need to use try/except to choose between the two.
>

Do you think that would be enough?

 diff --git a/scripts/dump-guest-memory.py b/scripts/dump-guest-memory.py
index 9956fc036c..f7c6635f15 100644
--- a/scripts/dump-guest-memory.py
+++ b/scripts/dump-guest-memory.py
@@ -314,8 +314,18 @@ def get_arch_phdr(endianness, elfclass):
 def int128_get64(val):
     """Returns low 64bit part of Int128 struct."""

-    assert val["hi"] == 0
-    return val["lo"]
+    try:
+        assert val["hi"] == 0
+        return val["lo"]
+    except gdb.error:
+        u64t = gdb.lookup_type('uint64_t').array(2)
+        u64 = val.cast(u64t)
+        if sys.byteorder == 'little':
+            assert u64[1] == 0
+            return u64[0]
+        else:
+            assert u64[0] == 0
+            return u64[1]

(I don't have a 32-bit system handy to check it, and cross-compilation with
m32 etc is tricky to get right, I am trying though)


> Paolo
>
> --
Marc-André Lureau