UB reproducibility

[o0101]

Hey @rurban

Thanks a lot for your work on SMHasher. It's really changed a lot in the last 3 years, all because of the effort you put in. The project's so much bigger than it was before, and better, thanks to your effort. I, and I'm sure a lot of others, really appreciate what you're doing.

Anyway, I'm sure you're super busy so I get if you can't get to this, or if anything makes it impossible for you and that's cool, everyone's got different degrees of freedom there, but I was just wondering about something and I have a pretty stupid question so I'm sorry.

Question is: how do I reproduce the "UB" claims you make against some of the hashes? Specifically I'm trying to repro on my hashes discohash and beamsplitter so I can try to address the UB flags you put against them. I tried,

$ clang++ -fsanitize=undefined *.cpp

on my discohash repo and it compiled fine. Sorry I'm not an expert in this and I know it's not your job, so if you can't reply that's cool. I'm just wondering, how do I do it like you did it so I can reproduce the behaviour you're seeing?

Anyway, I get if you're too busy to reply or if anything else means you can't get to this and that's cool, everyone has different degrees of freedom there, I wish you all the best in SMHasher and have a great 2021!

Cris

[rurban]

ubsan is a runtime check!

[o0101]

If you know how I can reproduce the behavior you're seeing and you let me know how to do that I might work on a fix.

[rurban]

Use the Debug CMAKE_BUILD_TYPE and run smhasher with your hash.

mkdir Debug
cd Debug
cmake .. -DCMAKE_BUILD_TYPE=Debug
make
./SMHasher BEBB4185

If the UB is fixed in-between please file a ticket.
For now it reports

--- Testing BEBB4185 "BEBB4185 64" POOR

[[[ Sanity Tests ]]]

Verification value 0xBEBB4185 ....... PASS
discohash.cpp:97:36: runtime error: load of misaligned address 0x6120000001e1 for type 'const uint64_t', which requires 8 byte alignment
0x6120000001e1: note: pointer points here
 2b 9d 0f  3c ae 43 09 bc 25 8f e6  cf 1b 9a 2f 99 89 b8 c9  22 f9 b9 11 f1 35 df 03  37 dc 62 fc 63
              ^ 
discohash.cpp:98:17: runtime error: load of misaligned address 0x6120000001e1 for type 'const uint64_t', which requires 8 byte alignment
0x6120000001e1: note: pointer points here
 2b 9d 0f  3c ae 43 09 bc 25 8f e6  cf 1b 9a 2f 99 89 b8 c9  22 f9 b9 11 f1 35 df 03  37 dc 62 fc 63

[o0101]

Thankyou @rurban ! ☺️