debug_trace Methods - Gas Simulation Bug (Fixed in v1.7.8)

Summary

Two related issues have been identified with debug_trace methods on nodes running versions earlier than v1.7.8. Both return a false "insufficient funds" error even when the affected transactions succeeded on-chain (receipt status 0x1).

Root Cause

When replaying a historical transaction, the EVM keeper deducts the gas fee upfront using current fee market parameters. A change in fee market behavior in an older Cronos version causes the recomputed fee to differ from what was originally charged at the time of inclusion. This makes the upfront deduction fail with an "insufficient funds" error, even though the transaction executed successfully on-chain.

The proposed fix bypasses the fee deduction for gas at the simulation level. While this resolves the error, it can result in incorrect gas accounting. We do not recommend relying on this simulation if you need exact gas accounting (for example, calculating precise CRO balances in a wallet). See "Implications of the Fix" below.

Issue 1: debug_traceBlockByNumber

On debug-enabled nodes running binary versions earlier than v1.7.8, debug_traceBlockByNumber (callTracer) returns a false error trace for one transaction per block across approximately 30 known mainnet blocks:

{
  "error": "rpc error: code = Internal desc = spendable balance X basecro is smaller than Y basecro: insufficient funds"
}

The issue is deterministic and reproducible across multiple node providers. Affected blocks:

2195345, 2216975, 2248485, 2398387, 2478809, 8066106, 8292697, 11577952, 11611854, 11614860, 11615746, 11615834, 11616122, 11616540, 11617030, 11617275, 11618202, 11624946, 11624962, 11627501, 11627662, 11628192, 11636446, 11644174, 11723806, 13467231, 13670292, 14058966, 14074873, 14146732

Note: This list may expand as further investigation continues.

Issue 2: debug_traceTransaction

On debug-enabled nodes running binary versions earlier than v1.7.8, debug_traceTransaction (callTracer) returns the following error:

{
  "error": {
    "code": -32000,
    "message": "rpc error: code = Unknown desc = rpc error: code = Internal desc = spendable balance X basecro is smaller than Y basecro: insufficient funds: unknown request"
  }
}

Resolution

Both issues are fixed in v1.7.8. Upgrade your node binary to v1.7.8 to resolve them.

The fix introduces an optional traceReplay boolean in the trace config. When enabled and the upfront fee deduction fails, the keeper logs a warning, continues the trace without charging the fee, and skips the matching gas refund.

  {                                                                              
    "jsonrpc": "2.0",
    "method": "debug_traceTransaction",                                          
    "params": ["0x<tx-hash>", { "tracer": "callTracer", "traceReplay": true }],  
    "id": 1                                                                      
  }     

Enable traceReplay only when a debug_trace call against an already-committed transaction fails with a gas/balance error. It is off by default.

Because the fix bypasses fee deduction at the simulation level, gas accounting for affected transactions will be approximate. The reported gas figure may be off by approximately the amount of gas consumed by the transaction itself.

Do not rely on trace results with traceReplay: true for exact gas accounting (e.g., calculating precise CRO balances in a wallet). Use it to inspect execution flow only. Omitting the flag (or setting it to false) preserves the previous strict behavior.