Effective gas implementation #290

ignasirv · 2023-05-24T12:25:07Z

Effective gas price implementation.
In order to be more precise with gasPrice and low tx fees, the sequencer is able to propose a reduction of the signed gasPrice. This param, effectiveGasPrice, is passed at the last bytes of the encoded tx and present in the batchL2Data. The final effectiveGasPrice is compute as:

effectiveGasPrice = floor((gasPrice * (effectivePercentage + 1)) / 256)

txGasPrice is replaced by effectiveGasPrice among tx processing

krlosMata

😸

main/process-tx.zkasm

invocamanman · 2023-05-26T11:00:17Z

nice ^^ :D

gumb0 · 2023-05-29T10:51:06Z

main/process-tx.zkasm

+        ; get value above 256 bits
+        ${_effGasPriceShifted >> 256} => D
+        ; compute ARITH
+        ${_effGasPriceShifted} => E              :ARITH


Should we have out of arith counters check for this code?
(or any other counters (steps, binary?) given that this adds quite a bit of computation)

Yes, I agree we should add an arith checker at beginning of process-tx.zkasm

gumb0 · 2023-05-29T11:49:50Z

main/process-tx.zkasm

+        ${_effGasPriceShifted / 256} => A        :MSTORE(txGasPrice)
+        ${_effGasPriceShifted % 256} => C
+        ; compute ARITH
+        E                                       :ARITH


Maybe I still don't quite understand how this works, so correct where if I'm wrong.

I believe the purpose of this ARITH is to contstrain the free calculations above (_effGasPriceShifted / 256 and _effGasPriceShifted % 256)

This ARITH line calculates AB + C and updates E and D.

What would stop malicious prover to return arbitrary value into A instead of _effGasPriceShifted / 256? This ARITH doesn't seem to constrain neither of registers values (unlike the first ARITH above?)
(for C it is more clear, it is at least checked for <256 afterwards)

Actually I think I understand now: it takes into account previous values of E and D and checks result of ARITH against them, because this expression doesn't have an assignment to register.

gumb0 · 2023-05-29T11:51:46Z

main/process-tx.zkasm

@@ -68,9 +70,34 @@ endCheckChainId:
                                        :CALL(isColdAddress) ; add tx.origin to touched addresses
        0                               :MSTORE(depth) ; Initial depth is 0

-;; Set gasPrice global var
+;; Set gasPrice global var depending on effectivePercentage [0-255] -> txGasPrice = Floor((gasPrice * (effectivePercentage + 1)) / 256)
+        ; _effGasPriceShifted = gasPrice * (effectivePercentage + 1)


Cosmetic: this comment is duplicated on line 83, maybe it's not needed here

gumb0 · 2023-05-29T11:52:41Z

main/process-tx.zkasm

-;; Set gasPrice global var
+;; Set gasPrice global var depending on effectivePercentage [0-255] -> txGasPrice = Floor((gasPrice * (effectivePercentage + 1)) / 256)
+        ; _effGasPriceShifted = gasPrice * (effectivePercentage + 1)
+        ; A => gasPrice


Cosmetic: notation with => is confusing here, because meaning is opposite of zkasm syntax

Suggested change

; A => gasPrice

; A = gasPrice

gumb0 · 2023-05-29T11:52:58Z

main/process-tx.zkasm

        $ => A                          :MLOAD(txGasPriceRLP)
-        A                               :MSTORE(txGasPrice)
+        ; B => effectivePercentage


Same as above

Suggested change

; B => effectivePercentage

; B = effectivePercentage

gumb0 · 2023-05-29T11:54:11Z

main/process-tx.zkasm

-        A                               :MSTORE(txGasPrice)
+        ; B => effectivePercentage
+        $ => B                          :MLOAD(effectivePercentageRLP)
+        ; B => [0, 255]


Cosmetic: if the comment supposed to explain the effect of the following line

Suggested change

; B => [0, 255]

; B = [1, 256]

review changes

chfast · 2023-05-30T09:26:27Z

main/load-tx-rlp.zkasm

@@ -285,6 +285,11 @@ vREADTx:
        A                               :MSTORE(txV)
        C + D => C                      :CALL(addBatchHashData)

+;; read effective percentage
+effectivePercentageTx:


This label is never called. Is this just a documentation?

yes, it is there for clarity

chfast · 2023-05-30T09:28:18Z

main/load-tx-rlp.zkasm

@@ -285,6 +285,11 @@ vREADTx:
        A                               :MSTORE(txV)
        C + D => C                      :CALL(addBatchHashData)

+;; read effective percentage
+effectivePercentageTx:
+        1 => D                          :CALL(getTxBytes)


The description of getTxBytes does not say what C is used for.

C description is at the very beginning of the rlp-processing: https://github.com/0xPolygonHermez/zkevm-rom/blob/main/main/load-tx-rlp.zkasm#L28

chfast · 2023-05-30T10:23:53Z

main/process-tx.zkasm

+        ; compute ARITH
+        E                                       :ARITH
+        ; check divisor > remainder
+        C => A


To confirm: LT treats arguments as unsigned. I.e. this will work in case C is "negative".

Is the usage of LT covered by CNT_BINARY - 100?

LT uses 1 binary, so yes.
LT treats arguments as unsigned, it compares two 256 bit scalars. To treat them as signed, we also have the registry SLT.
In case C is "negative" it will be treated as a Scalar

Effective gas implementation

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ignasirv requested review from krlosMata, laisolizq and invocamanman as code owners May 24, 2023 12:25

cla-bot bot added the cla-signed label May 24, 2023

ignasirv requested review from krlosMata, invocamanman, laisolizq, fractasy and zkronos73 and removed request for invocamanman, laisolizq, krlosMata and fractasy May 24, 2023 12:25

krlosMata approved these changes May 26, 2023

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invocamanman approved these changes May 26, 2023

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gumb0 reviewed May 29, 2023

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ignasirv and others added 2 commits May 29, 2023 13:09

Add arith checker at beginning of processTx

d09f1c5

review changes

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gumb0 reviewed May 29, 2023

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ignasirv force-pushed the feature/effective-gas-price branch from d09f1c5 to 33034b9 Compare May 29, 2023 12:47

Add arith checker at beginning of processTx

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ignasirv force-pushed the feature/effective-gas-price branch from 33034b9 to ac51215 Compare May 29, 2023 12:49

Merge pull request #291 from 0xPolygonHermez/feature/PR-push0-rlp-review

fcb8126

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chfast reviewed May 30, 2023

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krlosMata merged commit eb376cc into develop May 31, 2023
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Effective gas implementation #290

Effective gas implementation #290

ignasirv commented May 24, 2023 •

edited by krlosMata

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invocamanman commented May 26, 2023

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ignasirv May 29, 2023

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ignasirv May 30, 2023 •

edited

Effective gas implementation #290

Effective gas implementation #290

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ignasirv commented May 24, 2023 • edited by krlosMata

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ignasirv May 30, 2023 • edited

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ignasirv commented May 24, 2023 •

edited by krlosMata

ignasirv May 30, 2023 •

edited