Fuzzing Bitcoin Core with clang-16 #31922

1. 
   yancyribbens commented at 3:15 am on February 21, 2025: contributor

   Is there an existing issue for this?

   • I have searched the existing issues

   Current behaviour

   building fails during linking CXX executable bitcoin-wallet

    0[ 27%] Building CXX object src/util/CMakeFiles/bitcoin_util.dir/__/sync.cpp.o                                                                                            
    1[ 27%] Linking CXX static library libbitcoin_util.a                                                                                                                      
    2[ 27%] Built target bitcoin_util                                                                                                                                         
    3[ 27%] Building C object src/secp256k1/src/CMakeFiles/secp256k1_precomputed.dir/precomputed_ecmult.c.o                                                                   
    4[ 27%] Building C object src/secp256k1/src/CMakeFiles/secp256k1_precomputed.dir/precomputed_ecmult_gen.c.o                                                               
    5[ 27%] Built target secp256k1_precomputed                                                                                                                                
    6[ 28%] Building C object src/secp256k1/src/CMakeFiles/secp256k1.dir/secp256k1.c.o                                                                                        
    7[ 28%] Linking C static library ../lib/libsecp256k1.a                                                                                                                    
    8[ 28%] Built target secp256k1                                                                                                                                            
    9[ 28%] Building CXX object src/CMakeFiles/bitcoin-wallet.dir/bitcoin-wallet.cpp.o                                                                                        
   10[ 28%] Building CXX object src/CMakeFiles/bitcoin-wallet.dir/init/bitcoin-wallet.cpp.o                                                                                   
   11[ 28%] Building CXX object src/CMakeFiles/bitcoin-wallet.dir/wallet/wallettool.cpp.o                                                                                     
   12[ 28%] Linking CXX executable bitcoin-wallet                                                                                                                             
   13/usr/bin/ld: libbitcoin_common.a(bloom.cpp.o): undefined reference to symbol 'exp@@GLIBC_2.29'                                                                           
   14/usr/bin/ld: /lib/x86_64-linux-gnu/libm.so.6: error adding symbols: DSO missing from command line                                                                        
   15clang: error: linker command failed with exit code 1 (use -v to see invocation)                                                                                          
   16gmake[2]: *** [src/CMakeFiles/bitcoin-wallet.dir/build.make:138: src/bitcoin-wallet] Error 1                                                                             
   17gmake[1]: *** [CMakeFiles/Makefile2:650: src/CMakeFiles/bitcoin-wallet.dir/all] Error 2                                                                                  
   18gmake: *** [Makefile:146: all] Error 2
   

   Expected behaviour

   successful fuzz build.

   Steps to reproduce

   Using master branch:

   cmake -DCMAKE_C_COMPILER=/usr/bin/clang-16 -DCMAKE_CXX_COMPILER=/usr/bin/clang-16 --preset=libfuzzer

   Note here I am using clang-16 because the project fails to even begin the build process due to an error: uint256.h:133:19: error: call to consteval function 'util::ConstevalHexDigit' is not a constant expression. After finding the issue: #30947 I set the compiler to clang-16 which begins the build process but fails 28% through.

   Relevant log output

   No response

   How did you obtain Bitcoin Core

   Compiled from source

   What version of Bitcoin Core are you using?

   master@5b8fd7c3a6b8c9c6a9481d340c3bcc67e74993c3

   Operating system and version

   Debian GNU/Linux 12 (bookworm)

   Machine specifications

   No response

2. 
   maflcko commented at 8:25 am on February 21, 2025: member

   [ 28%] Linking CXX executable bitcoin-wallet

   There is no such executable in the fuzz build target. When using cmake, you will have to delete the build folder before configuring. Otherwise the build could be stale.

   Also, your system has clang-19 available to use, see https://packages.debian.org/bookworm/clang-19

   What are the exact steps to reproduce?

   I can’t reproduce this locally with:

   0rm -rf ./bld-fzz && cmake -DCMAKE_C_COMPILER=/usr/bin/clang-16 -DCMAKE_CXX_COMPILER=/usr/bin/clang++-16 -DSANITIZERS=fuzzer -DBUILD_FOR_FUZZING=ON -B ./bld-fzz && cmake --build ./bld-fzz -j $(nproc)
   

   Nor with

   0rm -rf ./bld-fzz && cmake -DCMAKE_C_COMPILER=/usr/bin/clang-19 -DCMAKE_CXX_COMPILER=/usr/bin/clang++-19 --preset=libfuzzer  -B ./bld-fzz && cmake --build ./bld-fzz -j $(nproc)
   

3. 
   yancyribbens commented at 10:38 pm on February 21, 2025: contributor

   What are the exact steps to reproduce?

   Following the docs here: https://github.com/bitcoin/bitcoin/blob/master/doc/fuzzing.md. cmake --preset=libfuzzer was fine, it was the next cmake --build build_fuzz that was failing.

   Looks like nuking ./bld-fzz did the trick. Should have thought to try a fresh checkout. Thanks!

4. yancyribbens closed this on Feb 21, 2025

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Contributors
yancyribbens maflcko