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Checkpoints::GetTotalBlocksEstimate will probably fail/produce wrong results on 0.10 branch (commit 047a898).

• No checkpoints - SIGSEGV accessing empty MapCheckpoints (i.e. std::map).
• N > 1 checkpoint - result is less than expected (by 1), but this probably doesn't make much sense
• Genesis block only - 0, but should be 1 - can probably break something

checkpoints.cpp:72-80

    int GetTotalBlocksEstimate()
    {
        if (!fEnabled)
            return 0;

        const MapCheckpoints& checkpoints = *Params().Checkpoints().mapCheckpoints;

        return checkpoints.rbegin()->first;
    }

Suggest to change checkpoints.cpp:79 from return checkpoints.rbegin()->first; to return checkpoints.rbegin()->first + 1;

Daemon (0.10 branch, commit 047a898) crashes in InvalidChainFound when run with empty blockchain and genesis block is invalid (fails validity check).

GDB stacktrace:

Program received signal EXC_BAD_ACCESS, Could not access memory.
Reason: KERN_INVALID_ADDRESS at address: 0x0000000000000000
CBlockIndex::GetBlockHash (this=0x0) at chain.h:215
215         return *phashBlock;
(gdb) bt
#0  CBlockIndex::GetBlockHash (this=0x0) at chain.h:215
#1  0x0000000100157816 in InvalidChainFound (pindexNew=0x10160d5f0) at main.cpp:1365
#2  0x000000010018106e in InvalidBlockFound (pindex=0x10160d5f0, state=@0x7fff5fbf7a70) at main.cpp:1386
#3  0x000000010017fa12 in ConnectTip (state=@0x7fff5fbf7a70, pindexNew=0x10160d5f0, pblock=0x10085de30) at main.cpp:1989
#4  0x00000001001540d0 in ActivateBestChainStep (state=@0x7fff5fbf7a70, pindexMostWork=0x10160d5f0, pblock=0x10085de30) at main.cpp:2117
#5  0x0000000100152a18 in ActivateBestChain (state=@0x7fff5fbf7a70, pblock=0x10085de30) at main.cpp:2170
#6  0x0000000100163397 in InitBlockIndex () at main.cpp:3098
#7  0x0000000100071b9f in AppInit2 (threadGroup=@0x7fff5fbff688) at init.cpp:1036
#8  0x0000000100005c40 in AppInit (argc=10, argv=0x7fff5fbff898) at bitcoind.cpp:148
#9  0x0000000100005f0a in main (argc=10, argv=0x7fff5fbff898) at bitcoind.cpp:185

main.cpp:1365:

LogPrintf("InvalidChainFound:  current best=%s  height=%d  log2_work=%.8g  date=%s\n",
      chainActive.Tip()->GetBlockHash().ToString(), chainActive.Height(), log(chainActive.Tip()->nChainWork.getdouble())/log(2.0),
      DateTimeStrFormat("%Y-%m-%d %H:%M:%S", chainActive.Tip()->GetBlockTime()));

chainActive.Tip() is NULL, possibly because we don't have an active chain/chain tip as the genesis block verification has just failed.

Seem to spend a lot of time in the loop of the second case ("use new nodes") of CAddrMan::Select_() (addrman.cpp) called from ThreadOpenConnections (net.cpp).
Regression was introduced in pull request bitcoin#5941 – fixed size vvNew and vvTried make us spend a lot of time selecting non-empty position (i.e. the position with peer address) when actual peer number is significantly less than ADDRMAN_NEW_BUCKET_COUNT*ADDRMAN_BUCKET_SIZE. Moreover, position selection is an expensive operation as it uses secure random number generation involving OpenSSL.
Issue bitcoin#1664 is probably related too, or at least the safe buggy behavior can be expected.