Some clarification after implementation (#533)

Findings after implementation FuelLabs/fuel-vm#623
FuelLabs · Nov 30, 2023 · 0904457 · 0904457
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diff --git a/src/fuel-vm/index.md b/src/fuel-vm/index.md
@@ -149,7 +149,7 @@ If script bytecode is present, transaction validation requires execution.
 The VM is [initialized](#vm-initialization), then:
 
 1. `$pc` and `$is` are set to the start of the transaction's script bytecode.
-1. `$ggas` and `$cgas` are set to `tx.gasLimit`.
+1. `$ggas` and `$cgas` are set to `tx.scriptGasLimit`.
 
 Following initialization, execution begins.
 

diff --git a/src/fuel-vm/instruction-set.md b/src/fuel-vm/instruction-set.md
@@ -2450,7 +2450,7 @@ Get [fields from the transaction](../tx-format/transaction.md).
 | name                                      | `imm`   | set `$rA` to                                                      |
 |-------------------------------------------|---------|-------------------------------------------------------------------|
 | `GTF_TYPE`                                | `0x001` | `tx.type`                                                         |
-| `GTF_SCRIPT_GAS_LIMIT`                    | `0x002` | `tx.gasLimit`                                                     |
+| `GTF_SCRIPT_GAS_LIMIT`                    | `0x002` | `tx.scriptGasLimit`                                               |
 | `GTF_SCRIPT_SCRIPT_LENGTH`                | `0x003` | `tx.scriptLength`                                                 |
 | `GTF_SCRIPT_SCRIPT_DATA_LENGTH`           | `0x004` | `tx.scriptDataLength`                                             |
 | `GTF_SCRIPT_INPUTS_COUNT`                 | `0x005` | `tx.inputsCount`                                                  |
@@ -2516,12 +2516,11 @@ Get [fields from the transaction](../tx-format/transaction.md).
 | `GTF_OUTPUT_CONTRACT_CREATED_STATE_ROOT`  | `0x308` | Memory address of `tx.outputs[$rB].stateRoot`                     |
 | `GTF_WITNESS_DATA_LENGTH`                 | `0x400` | `tx.witnesses[$rB].dataLength`                                    |
 | `GTF_WITNESS_DATA`                        | `0x401` | Memory address of `tx.witnesses[$rB].data`                        |
-| `GTF_POLICY_COUNT`                        | `0x500` | `count_ones(tx.policyTypes)`                                      |
-| `GTF_POLICY_TYPE`                         | `0x501` | `tx.policies[$rB].type`                                           |
-| `GTF_POLICY_GAS_PRICE`                    | `0x502` | `tx.policies[0x00].gasPrice`                                      |
-| `GTF_POLICY_WITNESS_LIMIT`                | `0x504` | `tx.policies[count_ones(0b11 & tx.policyTypes) - 1].witnessLimit` |
-| `GTF_POLICY_MATURITY`                     | `0x505` | `tx.policies[count_ones(0b111 & tx.policyTypes) - 1].maturity`    |
-| `GTF_POLICY_MAX_FEE`                      | `0x506` | `tx.policies[count_ones(0b1111 & tx.policyTypes) - 1].maxFee`     |
+| `GTF_POLICY_TYPES`                        | `0x500` | `tx.policies.policyTypes`                                         |
+| `GTF_POLICY_GAS_PRICE`                    | `0x501` | `tx.policies[0x00].gasPrice`                                      |
+| `GTF_POLICY_WITNESS_LIMIT`                | `0x502` | `tx.policies[count_ones(0b11 & tx.policyTypes) - 1].witnessLimit` |
+| `GTF_POLICY_MATURITY`                     | `0x503` | `tx.policies[count_ones(0b111 & tx.policyTypes) - 1].maturity`    |
+| `GTF_POLICY_MAX_FEE`                      | `0x504` | `tx.policies[count_ones(0b1111 & tx.policyTypes) - 1].maxFee`     |
 
 Panic if:
 

diff --git a/src/protocol/tx-validity.md b/src/protocol/tx-validity.md
@@ -144,7 +144,7 @@ def unavailable_balance(tx, asset_id) -> int:
     return sentBalance
 
 def fee_balance(tx, asset_id) -> int:
-    gas = tx.gasLimit + sum_predicate_gas_used(tx)
+    gas = tx.scriptGasLimit + sum_predicate_gas_used(tx)
     gasBalance = gasPrice * gas / GAS_PRICE_FACTOR
     bytesBalance = size(tx) * GAS_PER_BYTE * gasPrice / GAS_PRICE_FACTOR
     # Total fee balance
@@ -205,7 +205,7 @@ Once the free balances are computed, the [script is executed](../fuel-vm/index.m
 1. The unspent free balance `unspentBalance` for each asset ID.
 1. The unspent gas `unspentGas` from the `$ggas` register.
 
-The fees incurred for a transaction are `ceiling(((size(tx) * GAS_PER_BYTE) + (tx.gasLimit - unspentGas) + sum(tx.inputs[i].predicateGasUsed)) * tx.gasPrice / GAS_PRICE_FACTOR)`.
+The fees incurred for a transaction are `ceiling(((size(tx) * GAS_PER_BYTE) + (tx.scriptGasLimit - unspentGas) + sum(tx.inputs[i].predicateGasUsed)) * tx.gasPrice / GAS_PRICE_FACTOR)`.
 
 `size(tx)` includes the entire transaction serialized according to the transaction format, including witness data.
 This ensures every byte of block space either on Fuel or corresponding DA layer can be accounted for.

diff --git a/src/tx-format/transaction.md b/src/tx-format/transaction.md
@@ -55,23 +55,24 @@ enum ReceiptType : uint8 {
 }
 ```
 
-| name               | type                        | description                                          |
-|--------------------|-----------------------------|------------------------------------------------------|
-| `gasLimit`         | `uint64`                    | Gas limit for transaction (including predicate gas). |
-| `scriptLength`     | `uint16`                    | Script length, in instructions.                      |
-| `scriptDataLength` | `uint16`                    | Length of script input data, in bytes.               |
-| `policyTypes`      | `uint32`                    | Bitfield of used policy types.                       |
-| `inputsCount`      | `uint8`                     | Number of inputs.                                    |
-| `outputsCount`     | `uint8`                     | Number of outputs.                                   |
-| `witnessesCount`   | `uint8`                     | Number of witnesses.                                 |
-| `receiptsRoot`     | `byte[32]`                  | Merkle root of receipts.                             |
-| `script`           | `byte[]`                    | Script to execute.                                   |
-| `scriptData`       | `byte[]`                    | Script input data (parameters).                      |
-| `policies`         | [Policy](./policy.md)`[]`   | List of policies, sorted by PolicyType.              |
-| `inputs`           | [Input](./input.md)`[]`     | List of inputs.                                      |
-| `outputs`          | [Output](./output.md)`[]`   | List of outputs.                                     |
-| `witnesses`        | [Witness](./witness.md)`[]` | List of witnesses.                                   |
-
+| name               | type                        | description                             |
+|--------------------|-----------------------------|-----------------------------------------|
+| `scriptGasLimit`   | `uint64`                    | Gas limits the script execution.        |
+| `scriptLength`     | `uint16`                    | Script length, in instructions.         |
+| `scriptDataLength` | `uint16`                    | Length of script input data, in bytes.  |
+| `policyTypes`      | `uint32`                    | Bitfield of used policy types.          |
+| `inputsCount`      | `uint8`                     | Number of inputs.                       |
+| `outputsCount`     | `uint8`                     | Number of outputs.                      |
+| `witnessesCount`   | `uint8`                     | Number of witnesses.                    |
+| `receiptsRoot`     | `byte[32]`                  | Merkle root of receipts.                |
+| `script`           | `byte[]`                    | Script to execute.                      |
+| `scriptData`       | `byte[]`                    | Script input data (parameters).         |
+| `policies`         | [Policy](./policy.md)`[]`   | List of policies, sorted by PolicyType. |
+| `inputs`           | [Input](./input.md)`[]`     | List of inputs.                         |
+| `outputs`          | [Output](./output.md)`[]`   | List of outputs.                        |
+| `witnesses`        | [Witness](./witness.md)`[]` | List of witnesses.                      |
+
+Given helper `max_gas()` returns the maximum gas that the transaction can use.
 Given helper `len()` that returns the number of bytes of a field.
 Given helper `count_ones()` that returns the number of ones in the binary representation of a field.
 Given helper `count_variants()` that returns the number of variants in an enum.
@@ -84,7 +85,7 @@ Transaction is invalid if:
 - `scriptDataLength > MAX_SCRIPT_DATA_LENGTH`
 - `scriptLength * 4 != len(script)`
 - `scriptDataLength != len(scriptData)`
-- `gasLimit > MAX_GAS_PER_TX`
+- `max_gas(tx) > MAX_GAS_PER_TX`
 - No policy of type `PolicyType.GasPrice`
 - `count_ones(policyTypes) > count_variants(PolicyType)`
 - `policyTypes > sum_variants(PolicyType)`
@@ -116,6 +117,7 @@ The receipts root `receiptsRoot` is the root of the [binary Merkle tree](../prot
 | `outputs`              | [Output](./output.md)`[]`   | List of outputs.                                  |
 | `witnesses`            | [Witness](./witness.md)`[]` | List of witnesses.                                |
 
+Given helper `max_gas()` returns the maximum gas that the transaction can use.
 Given helper `count_ones()` that returns the number of ones in the binary representation of a field.
 Given helper `count_variants()` that returns the number of variants in an enum.
 Given helper `sum_variants()` that sums all variants of an enum.
@@ -133,6 +135,7 @@ Transaction is invalid if:
 - The keys of `storageSlots` are not in ascending lexicographic order
 - The computed contract ID (see below) is not equal to the `contractID` of the one `OutputType.ContractCreated` output
 - `storageSlotsCount > MAX_STORAGE_SLOTS`
+- `max_gas(tx) > MAX_GAS_PER_TX`
 - The [Sparse Merkle tree](../protocol/cryptographic-primitives.md#sparse-merkle-tree) root of `storageSlots` is not equal to the `stateRoot` of the one `OutputType.ContractCreated` output
 - No policy of type `PolicyType.GasPrice`
 - `count_ones(policyTypes) > count_variants(PolicyType)`