tracing: drop block_connected hash.toString() arg

The tracepoint `validation:block_connected` was introduced in #22006.
The first argument was the hash of the connected block as a pointer
to a C-like String. The last argument passed the hash of the
connected block as a pointer to 32 bytes. The hash was only passed as
string to allow `bpftrace` scripts to print the hash. It was
(incorrectly) assumed that `bpftrace` cannot hex-format and print the
block hash given only the hash as bytes.

The block hash can be printed in `bpftrace` by calling
`printf("%02x")` for each byte of the hash in an `unroll () {...}`.
By starting from the last byte of the hash, it can be printed in
big-endian (the block-explorer format).

```C
  $p = $hash + 31;
  unroll(32) {
      $b = *(uint8*)$p;
      printf("%02x", $b);
      $p -= 1;
  }
```

See also: https://github.com/bitcoin/bitcoin/pull/22902#discussion_r705176691

This is a breaking change to the block_connected tracepoint API, however
this tracepoint has not yet been included in a release.

1 files changed, 3 insertions, 4 deletions

diff --git a/src/validation.cpp b/src/validation.cpp
index 4b9a61320c..78559a8ee6 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -1877,14 +1877,13 @@ bool CChainState::ConnectBlock(const CBlock& block, BlockValidationState& state,
     int64_t nTime5 = GetTimeMicros(); nTimeIndex += nTime5 - nTime4;
     LogPrint(BCLog::BENCH, "    - Index writing: %.2fms [%.2fs (%.2fms/blk)]\n", MILLI * (nTime5 - nTime4), nTimeIndex * MICRO, nTimeIndex * MILLI / nBlocksTotal);
 
-    TRACE7(validation, block_connected,
-        block.GetHash().ToString().c_str(),
+    TRACE6(validation, block_connected,
+        block.GetHash().data(),
         pindex->nHeight,
         block.vtx.size(),
         nInputs,
         nSigOpsCost,
-        GetTimeMicros() - nTimeStart, // in microseconds (µs)
-        block.GetHash().data()
+        GetTimeMicros() - nTimeStart // in microseconds (µs)
     );
 
     return true;