__builtin_clz takes an unsigned int, it isn't overloaded for different
types. This meant that we were computing log2 by counting the
leading bits in a 32-bit value and using that result as if it were the
number of bits in a 64-bit value. This meant that our alignment values
were 2^32 times as big as they should be. This mostly didn't matter,
because we then truncated the result to 32 bits and the wrapping gave
the correct answer.
Unfortunately, this was undefined behaviour and, at sufficiently high
optimisation levels, this resulted in the value being optimised away,
leading to odd results.
Add a flag to indicate that instance variables have an extended type
encoding.
Remove the alignment field and replace it with 6 bits from the flags
field. We only support power of two alignments, so we may as well store
them in log form, which means we can save a field. Note that this
doesn't actually save us any space except on 32-bit platforms, because
alignment means that we end up with extra padding at the end of the
struct.
Several of the structures now end with an array of structures that may
have other fields added to them that the runtime doesn't know about yet
by a compiler. Rather than indexing into them directly, we must call an
accessor to find the correct address.
A few of the places where accesses were replaced were in functions where
it is safe because they only deal with versions of the structures that
are dynamically allocated (and will therefore have the correct size).
This was done to simplify future auditing: these fields should be
accessed directly only from the accessor functions in the header and
from the upgraders (currently in legacy.c).
Also fix a few bugs where the sizes weren't being filled in.
We're now using a new class and category structure and auto-upgrading the old ones. Other changes:
- The Ivar structure now points to the ivar offset variable, so we can more easily find it.
- Categories can now add properties.
The new structure has extra fields for alignment and flags (e.g.
ownership).
Old structures are auto-upgraded at load time, so the rest of the code
can assume the presence of the new structure type.
Added fields to the end of the class structure for strong / weak ivar bitmaps (not yet generated by any compiler).
Fixed definition of __sync_swap() so that it works on GCC again.
David Chisnall
David Chisnall
David Chisnall
theraven