Rework tests to prevent root context calls and remove kernel workarounds

[phklive]

Feature description

The testing framework in Miden-base executes code directly from the kernel root context. Which should not be possible during "normal" execution of the virtual machine in the context of the Miden rollup.

This method makes some of the checks fail and forces us to use workarounds in the kernel code. One example is the following code:

miden-base/miden-lib/asm/kernels/transaction/lib/account.masm

Lines 543 to 563 in e5f5101

	# get procedure info (PROC_ELEMENTS, storage_offset) from memory stored at index
	exec.get_procedure_info
	# In production:
	# => [PROC_ELEMENTS, storage_offset, PROC_ROOT]
	# During testing:
	# => [255, PROC_ROOT]
	# TODO: Fix VM caller == [0,0,0,0] bug and remove this check
	# check if get_procedure_info returned 255
	dup push.255 neq
	# => [is_255, index, PROC_ROOT]
	# verify that PROC_ROOT matches returned procedure information
	if.true
	# verify that PROC_ROOT exists in memory at index
	movup.4 movdn.8 assert_eqw.err=ERR_PROC_NOT_PART_OF_ACCOUNT_CODE
	# => [storage_offset]
	else
	# drop PROC_ROOT
	movdn.4 dropw
	end

miden-base/miden-lib/asm/kernels/transaction/lib/account.masm

Lines 507 to 525 in e5f5101

	# TODO: Fix VM caller == [0,0,0,0] bug and remove this check
	# check if index == 255
	dup push.255 neq
	# => [is_255, index]
	# load procedure information from memory
	if.true
	# check that index < number of procedures contained in the account code
	dup exec.memory::get_num_account_procedures lt assert.err=ERR_PROC_INDEX_OUT_OF_BOUNDS
	# => [index]
	# get procedure section ptr
	push.2 mul exec.memory::get_account_procedures_section_offset add dup push.1 add
	# => [proc_ptr, offset_ptr]
	# load procedure information from memory
	mem_load swap padw movup.4 mem_loadw
	# => [PROC_ROOT, storage_offset]
	end

miden-base/miden-tx/src/host/account_procs.rs

Lines 92 to 96 in e5f5101

	// mock account method for testing from root context
	// TODO: figure out if we can get rid of this
	if proc_root == Digest::default() {
	return Ok(255);
	}

These pieces of code check if the caller is equal to [0,0,0,0] which would only happen if the call is being made directly from the kernel context and not from a user context, which should be the case in a general circumstances.

We need to remove this workaround by:

1. Reworking how we test code in Miden-base, without making calls from root context
2. Making sure that the caller is not equal to [0,0,0,0] the call having been made from a valid user context
3. Remove the conditional code from account.masm here and here and account_procs.rs

Why is this feature needed?

We need to make sure that we remove workarounds as soon as possible to keep the cleanest codebase possible.

[igamigo]

I think I got some of this working but not sure if there is any alternative: Basically I'm exposing more calls through the account interface and calling instead of execing. And then of course assembling/running the code or transaction with the new account code. Does that sound OK or is there a better approach? Here's a rough draft, most tests pass except 2 or 3 for which the interface is not correctly set up I think.

[bobbinth]

I think this approach works (assuming we can make all tests work like that).

[igamigo]

Closed by #857