ethminer failes to generate DAG file for any block larger than 3870000 (serious bug)

[kenshirothefist]

When trying to generate DAG file for any block larger than 3870000, it will only produce a 0-size file.

Try this:

ethminer.exe -D 3870000

It will run just of a few seconds, generate 0-bytes file "full-R23-3868abc5dcee2334" and exit (or even crash in some cases).

If you try to generate DAG for any previous block, for example:

ethminer.exe -D 3840000

it will work just fine.

[nicehashdev]

Hint: I suspect this may something to do with "int" overflow? Since DAG file is now nearly 2^32 / 2 in size, standard int would overflow at that number.

[gumb0]

Thank you for reporting this!

@nicehashdev is right, good old int overflow happens for me on Windows here:
https://github.com/ethereum/cpp-ethereum/blob/develop/libethash/io.c#L94

@kenshirothefist Which OS do you use?

[kenshirothefist]

@gumb0 I was testing under Windows 7 / 10.

[gumb0]

Thanks, I'll look into this

[gumb0]

@kenshirothefist Could you please check if this branch works for you https://github.com/ethereum/cpp-ethereum/tree/fix-mining-fseek ?

[kenshirothefist]

@gumb0 I just tested fix-mining-fseek branch under Ubuntu 16 and it works ... DAG file was correctly generated for "-D 3870000". So this looks good. I'll also test under Windows, but I have to prepare build env...

[gumb0]

@kenshirothefist Thanks for your help, it works for me on Windows.