Perform byte-endian conversion for 256-bit numeric values, but not 256-bit
hashes. These conversions are necessary for EVMC binary compatibility.
In new EVMC, all host-side conversions are explicit, calling `flip256`.
These conversions are performed in the EVMC "glue" code, which deals with the
binary interface, so the host services aren't aware of conversions.
We intend to skip these conversions when Nimbus host calls Nimbus EVM, even
when it's a shared library, using a negotiated EVMC extension. But for now
we're focused on correctness and cross-validation with third party EVMs.
The overhead of endian conversion is not too high because most EVMC host calls
access the database anyway. `getTxContext` does not, so the conversions from
that are cached here. Also, well-optimised EVMs don't call it often.
It is arguable whether endian conversion should occur for storage slots (`key`).
In favour of no conversion: Slot keys are 32-byte blobs, and this is clear in
the EVMC definition where slot keys are `evmc_bytes32` (not `evmc_uint256be`),
meaning treating as a number is _not_ expected by EVMC. Although they are
often small numbers, sometimes they are a hash from the contract code plus a
number. Slot keys are hashed on the host side with Keccak256 before any
database calls, so the host side does not look at them numerically.
In favour of conversion: They are often small numbers and it is helpful to log
them as such, rather than a long string of zero digits with 1-2 non-zero. The
representation in JSON has leading zeros removed, like a number rather than a
32-byte blob. There is also an interesting space optimisation when the keys
are used unhashed in storage.
Nimbus currently treats slot keys on the host side as numbers, and the tests
pass when endian conversion is done. So to remain consistent with other parts
of Nimbus we convert slot keys.
Signed-off-by: Jamie Lokier <jamie@shareable.org>
This changes fixes a bug in `CREATE2` ops when used with EVMC.
Because it changes the salt type, it affects non-EVMC code as well.
The salt was passed through EVMC with the wrong byte order, although this went
unnoticed as the Nimbus host flipped the byte order before using it.
This was found when running Nimbus with third-party EVM,
["evmone"](https://github.com/ethereum/evmone).
There are different ways to remedy this.
If treated as a number, Nimbus EVM would byte-flip the value when calling EVMC,
then Nimbus host would flip the received value. Finally, it would be flipped a
third time when generating the address in `generateSafeAddress`. The first two
flips can be eliminated by negotiation (like other numbers), but there would
always be one flip.
As a bit pattern, Nimbus EVM would flip the same way it does when dealing with
hashes on the stack (e.g. with `getBlockHash`). Nimbus host wouldn't flip at
all - and when using third-party EVMs there would be no flips in Nimbus.
Because this value is not for arithmetic, any bit pattern is valid, and there
shouldn't be any flips when using a third-party EVM, the bit-pattern
interpretation is favoured. The only flip is done in Nimbus EVM (and might be
eliminated in an optimised version).
As suggested, we'll define a new "opaque 256 bits" type to hold this value.
(Similar to `Hash256`, but the salt isn't necessarily a hash.)
Signed-off-by: Jamie Lokier <jamie@shareable.org>
We'll re-enable endian conversions based on a negotiated run-time option later,
but for now let's remove one complication to testing the new EVMC paths, and
also gain a little performance.
Signed-off-by: Jamie Lokier <jamie@shareable.org>
Jamie Lokier
andri lim