[Spice-devel] [PATCH] demarshall: Add safe method for unaligned byte access.

[Frediano Ziglio]

> > Usefull for ARM. Enable with "USE_MEMCPY" define.
> >  Should be better to add "--use-memcpy" to configure.ac
> > 
> > Signed-off-by: Anton D. Kachalov <mouse at yandex-team.ru>
> > ---
> >  python_modules/demarshal.py | 29 +++++++++++++++++++----------
> >  1 file changed, 19 insertions(+), 10 deletions(-)
> > 
> > diff --git a/python_modules/demarshal.py b/python_modules/demarshal.py
> > index 209eafc..158acd6 100644
> > --- a/python_modules/demarshal.py
> > +++ b/python_modules/demarshal.py
> > @@ -47,17 +47,25 @@ def write_parser_helpers(writer):
> >              type = "%sint%d" % (sign, size)
> >              swap = "SPICE_BYTESWAP%d" % size
> >              if size == 8:
> > -                writer.macro("read_%s" % type, "ptr", "(*((%s_t *)(ptr)))"
> > %
> > type)
> > -                writer.macro("write_%s" % type, "ptr, val", "*(%s_t
> > *)(ptr)
> > = val" % (type))
> > +                writer.macro("read_%s" % type, "val, ptr", "*(val) =
> > (*((%s_t *)(ptr)))" % type)
> > +                writer.macro("write_%s" % type, "ptr, val", "*(%s_t
> > *)(ptr)
> > = *val" % (type))
> >              else:
> > -                writer.macro("read_%s" % type, "ptr", "((%s_t)%s(*((%s_t
> > *)(ptr))))" % (type, swap, utype))
> > -                writer.macro("write_%s" % type, "ptr, val", "*(%s_t
> > *)(ptr)
> > = %s((%s_t)val)" % (utype, swap, utype))
> > +                writer.macro("read_%s" % type, "val, ptr", "*(val) =
> > ((%s_t)%s(*((%s_t *)(ptr))))" % (type, swap, utype))
> > +                writer.macro("write_%s" % type, "ptr, val", "*(%s_t
> > *)(ptr)
> > = %s(*(%s_t)val)" % (utype, swap, utype))
> >      writer.writeln("#else")
> > +    writer.writeln("#ifdef USE_MEMCPY")
> >      for size in [8, 16, 32, 64]:
> >          for sign in ["", "u"]:
> >              type = "%sint%d" % (sign, size)
> > -            writer.macro("read_%s" % type, "ptr", "(*((%s_t *)(ptr)))" %
> > type)
> > -            writer.macro("write_%s" % type, "ptr, val", "(*((%s_t
> > *)(ptr)))
> > = val" % type)
> > +            writer.macro("read_%s" % type, "val, ptr", "memcpy(val, ptr,
> > sizeof(%s_t))" % type)
> > +            writer.macro("write_%s" % type, "ptr, val", "memcpy(ptr, val,
> > sizeof(%s_t))" % type)
> > +    writer.writeln("#else")
> > +    for size in [8, 16, 32, 64]:
> > +        for sign in ["", "u"]:
> > +            type = "%sint%d" % (sign, size)
> > +            writer.macro("read_%s" % type, "val, ptr", "*(val) = (*((%s_t
> > *)(ptr)))" % type)
> > +            writer.macro("write_%s" % type, "ptr, val", "(*((%s_t
> > *)(ptr)))
> > = *val" % type)
> > +    writer.writeln("#endif")
> >      writer.writeln("#endif")
> >  
> >      for size in [8, 16, 32, 64]:
> > @@ -67,7 +75,7 @@ def write_parser_helpers(writer):
> >              ctype = "%s_t" % type
> >              scope = writer.function("SPICE_GNUC_UNUSED consume_%s" % type,
> >              ctype, "uint8_t **ptr", True)
> >              scope.variable_def(ctype, "val")
> > -            writer.assign("val", "read_%s(*ptr)" % type)
> > +            writer.statement("read_%s(&val, *ptr)" % type)
> >              writer.increment("*ptr", size // 8)
> >              writer.statement("return val")
> >              writer.end_block()
> > @@ -96,7 +104,7 @@ def write_read_primitive(writer, start, container, name,
> > scope):
> >      var = "%s__value" % (name.replace(".", "_"))
> >      if not scope.variable_defined(var):
> >          scope.variable_def(m.member_type.c_type(), var)
> > -    writer.assign(var, "read_%s(pos)" % (m.member_type.primitive_type()))
> > +    writer.statement("read_%s(&%s, pos)" %
> > (m.member_type.primitive_type(),
> > var))
> >      return var
> >  
> >  def write_write_primitive(writer, start, container, name, val):
> > @@ -105,7 +113,8 @@ def write_write_primitive(writer, start, container,
> > name,
> > val):
> >      writer.assign("pos", start + " + " + container.get_nw_offset(m, "",
> >      "__nw_size"))
> >  
> >      var = "%s__value" % (name)
> > -    writer.statement("write_%s(pos, %s)" %
> > (m.member_type.primitive_type(),
> > val))
> > +    writer.assign(var, val)
> > +    writer.statement("write_%s(pos, &%s)" %
> > (m.member_type.primitive_type(),
> > var))
> >      return var
> >  
> >  def write_read_primitive_item(writer, item, scope):
> > @@ -114,7 +123,7 @@ def write_read_primitive_item(writer, item, scope):
> >      writer.error_check("pos + %s > message_end" %
> >      item.type.get_fixed_nw_size())
> >      var = "%s__value" % (item.subprefix.replace(".", "_"))
> >      scope.variable_def(item.type.c_type(), var)
> > -    writer.assign(var, "read_%s(pos)" % (item.type.primitive_type()))
> > +    writer.statement("read_%s(&%s, pos)" % (item.type.primitive_type(),
> > var))
> >      return var
> >  
> >  class ItemInfo:
> 
> Anton, which architecture it's your machine. Could be that using some
> gcc options would make the compiler generate only aligned access
> instructions.
> 

Can you try to add  -mno-unaligned-access option to your CFLAGS ?

Frediano