Patch the instruction discriminant to be 4 bytes

[steveluscher]

Warning

I'm pretty sure that this is not landable, because if the legacy built-in and this program have different discriminator sizes, then the actual instruction data will not line up when we switch from one to the other. I couldn't find a way to configure Shank macros to produce 4-byte discriminants.

Fixes: #2.

[steveluscher]

Paging @lorisleiva, Shank wizard. Is there a way to convince Shank to produce 4-byte instruction discriminators other than to hot-patch the idl?

[buffalojoec]

You can maybe update the comment here to say "this program" instead of "the legacy native program", since they are both the same, but idc.

[lorisleiva]

Sadly no, Shank doesn't support custom enum discriminants. You could use a Codama visitor to update this but since we're currently saving the Anchor IDL and not the Codama one, your solution is currently the best thing to do.

[buffalojoec]

This can land. The program's instructions aren't serialized or deserialized using Shank, but rather bincode.

loader-v3/program/src/instruction.rs

Lines 378 to 382 in 1716195

	Instruction::new_with_bincode(
	crate::id(),
	&LoaderV3Instruction::InitializeBuffer,
	accounts,
	)

This patch would just be for clients, and until Shank supports u32 (or we have Codama macros), this is fine IMO.

[steveluscher]

But hang on, if I call, say DeployWithMaxDataLen which actually has instruction data, and the old program is like:

2 0 0 0 1 1 1 1 1 1 1 1
^^^^^^^ ^^^^^^^^^^^^^^^
disc    max_data_len

But the new program is like:

2 1 1 1 1 1 1 1 1
^ ^^^^^^^^^^^^^^^
d max_data_len

And then we have clients sending the old data to the new program, wouldn't it get interpreted like this?

2 0 0 0 1 1 1 1
^ ^^^^^^^^^^^^^
d max_data_len

[buffalojoec]

But the new program is like:

This is what I'm saying, the new program is not using u8 discriminators. It's using u32, since I've derived serde's Serialize and Deserialize on them and I use bincode to pack/unpack within the helpers and processor.

loader-v3/program/src/processor.rs

Line 25 in 1716195

fn limited_deserialize<T>(input: &[u8]) -> Result<T, ProgramError>

In other words, it's exactly the same instruction implementation as the builtin.

[buffalojoec]

You can maybe update the comment here to say "this program" instead of "the legacy native program", since they are both the same, but idc.

[lorisleiva]

Sadly no, Shank doesn't support custom enum discriminants. You could use a Codama visitor to update this but since we're currently saving the Anchor IDL and not the Codama one, your solution is currently the best thing to do.