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Fixed-Gas CFG #237

merged 69 commits into from Jun 6, 2021

Fixed-Gas CFG #237

merged 69 commits into from Jun 6, 2021


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@YaronWittenstein YaronWittenstein commented May 20, 2021


Prior to executing a transaction, we should be able to tell what its price will be in terms of gas units. (for now, we only deal with fixed-gas Wasm apps under SVM).

In the future, we could extend the gas pricing to support metering. (and consequently also not only fixed-gas Wasm code)

Since we only deal with fixed-gas Wasm programs for now - we compute the gas costs offline before actually executing the transaction.

Even though the internals of SVM will infer a Gas minimum and maximum range to be paid, in practice the maximum gas units will be charged off the sender.

In case a transaction has not enough gas (i.e the gas limit is too small) the transaction should be discarded.
(it won't be part of a block and won't get a chance to execute at all).

In order to compute the price of a transaction we first need to be able to tell the price of a function. (Wasm function).
So, after making sure we have no loop neither call cycles in the Call-Graph (this is done as part of the validation phase when deploying a template) - we can proceed to price-per-function computation.

This PR lays the foundations for achieving that. Given a Wasm function, it constructs in one scan a corresponding CFG (see Control-Flow Graph) that simulates different execution paths of a function.

The Function CFG building algorithm is documented here:

Being able to construct the function CFG in a single pass is crucial since it adds security. Otherwise, an attacker would try to generate valid fixed-gas Wasm inputs that would try to take advantage of that.

A next PR will implement the actual pricing part - it will consume functions CFGs one-by-one and compute the price for different paths within a function. In the end, it will be able to report the minimum and maximum prices for the function CFG.
Again - it could be done since the CFG of a fixed-gas Wasm function contains no loops/call-cycles.

Implemented the `svm_allocate` host function.

adding some debugging printing to the new `svm_allocate` host function.

WIP: computing the `returns` byte-size for a function (sdk-macros)

* `calldata` is allocated on instance only when non-empty.

The `svm-sdk` relies on the host function for Wasm targeted code and on the default global allocator otherwise.

adding `svm_sdk_std::panic` (aborts for Wasm and unwinds otherwise)

WIP: adding an explicit feature flag for the host static allocation.

svm-codec is using the default global-alloactor (not the "static allocation")

codec - js tests pass (commenting the `verify_data` for now)

tests pass

CI - running only on Windows + running the tests 10 times (there seems to be a sporadic failures)

CI - skipping the build stage

svm-sdk-std: exposing Rust `Vec`

svm-sdk-std: using `panic!`

running only the `svm-runtime` crate tests.

Removing `wabt` (using only `wat`) - it takes much less time to build.

using cache action v2

Adding GitHub Action for LLVM

Adding caching to the llvm


Returning back the original LLVM action for Windows

adding feature-flags `default-cranelift` and `default-llvm`

trying to run CI against `llvm`

running tests with a single thread

runtime - removing two ignored tests related to gas-metering

Commenting a test

runtime: ignoring all tests except one

running tests in dev-mode

Building on Linux and macOS

svm-sdk-std: returning back Rust `Vec`

Commenting part of the problematic test

Commenting another part of the problematic test

uncomment part of the problematic test

cbindgen version bump

problemtic test - wasm input file "runtime_calldata.wasm" isn't using the "static-alloc"

problemtic test: input wasm is being compiled with less code and no `.cargo/config` file

Uncommenting all the problematic test

Trying to locate the bug

Trying again to pinpoint the bug

Adding asserts against setting explicitly empty `returndata`

WIP: debugging

WIP: debugging...

WIP: debugging...

skipping the last CI stages for now...

WIP: trying to locate the cause of the bug...


commenting the "static-alloc" related code from `svm-sdk-alloc`


Trying again to make the test fail

Trying to figure out whether the #[endpoint] return-type has anything to do with the bug...

Commenting "Storage" from the wasm input of the failing test...

More debugging the root cause of the problem


adding "Cache workspace" step

Splitting cargo caching into isloated steps.

adding "Dump GitHub context" step.

CI: changing to `crates/runtime` before running the tests

Try again to run CI...

Try again

CI: disabling LLVM installation for now (Windows)

Trying again to reproduce a broken CI on Windows...

Checking whether the bug has something to do with `svm_sdk::Address`

Trying to find a minimal failing input using `Amount`

WIP: Debugging...

WIP: removing the parameter from the problematic endpoint

This should pass (not using `endpoint`)

This should fail again...

`ExtHost#get_calldata` - returning a static data

Re-compile the wasm input

Empty `endpoint` prologue.



Trying to narrow the bug


Narrowing the epilogue part

should fail...

Uncommenting part of the epilogue

@YaronWittenstein YaronWittenstein self-assigned this May 20, 2021
@YaronWittenstein YaronWittenstein added the big Big-sized task label May 20, 2021
@YaronWittenstein YaronWittenstein mentioned this pull request May 20, 2021
@YaronWittenstein YaronWittenstein force-pushed the fixed-gas-cfg branch 8 times, most recently from 88d99cd to 11104df Compare May 22, 2021 15:43
@YaronWittenstein YaronWittenstein marked this pull request as ready for review May 22, 2021 15:45
@YaronWittenstein YaronWittenstein force-pushed the fixed-gas-cfg branch 3 times, most recently from 1e5cd98 to 8de4e95 Compare May 24, 2021 06:31
@YaronWittenstein YaronWittenstein merged commit 3ee0b03 into master Jun 6, 2021
@YaronWittenstein YaronWittenstein deleted the fixed-gas-cfg branch June 6, 2021 14:51
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