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

[Paolo Bonzini]

On 10/03/2017 11:54, Marc-André Lureau wrote:
> Hi
> 
> On Fri, Mar 10, 2017 at 2:00 PM Paolo Bonzini <address@hidden
> <mailto: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
>     <mailto: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)

Yes, this should work.

Paolo