As seen in the vbox-tools upload to migrate from LLVM 19 to 21, the
fuzzer libraries are not used anymore (or not found) when built with
LLVM 21. You can reproduce that when building with the unversioned clang:

[...]
     LD            tests/vb2_keyblock_fuzzer
clang -o
/packages/tmp/vboot-utils-0~R106-15054.B+dfsg/build/tests/vb2_keyblock_fuzzer
-Wl,-z,relro -Wl,-z,now -Wl,--gc-sections -pie -Xlinker 
--allow-multiple-definition -fsanitize=fuzzer 
/packages/tmp/vboot-utils-0~R106-15054.B+dfsg/build/tests/vb2_keyblock_fuzzer.o
  /packages/tmp/vboot-utils-0~R106-15054.B+dfsg/build/vboot_fw.a -lrt -luuid
/usr/bin/x86_64-linux-gnu-ld.bfd/usr/bin/x86_64-linux-gnu-ld.bfd: cannot
find : cannot find
/usr/lib/llvm-21/lib/clang/21/lib/x86_64-pc-linux-gnu/libclang_rt.fuzzer.a:
/usr/lib/llvm-21/lib/clang/21/lib/x86_64-pc-linux-gnu/libclang_rt.fuzzer.a:
No such file or directory
No such file or directory
/usr/bin/x86_64-linux-gnu-ld.bfd: cannot find
/usr/bin/x86_64-linux-gnu-ld.bfd: cannot find
/usr/lib/llvm-21/lib/clang/21/lib/x86_64-pc-linux-gnu/libclang_rt.fuzzer_interceptors.a:
/usr/lib/llvm-21/lib/clang/21/lib/x86_64-pc-linux-gnu/libclang_rt.fuzzer_interceptors.aNo
such file or directory:
No such file or directory
/usr/bin/x86_64-linux-gnu-ld.bfd/usr/bin/x86_64-linux-gnu-ld.bfd: cannot
find : cannot find
/usr/lib/llvm-21/lib/clang/21/lib/x86_64-pc-linux-gnu/libclang_rt.ubsan_standalone.a/usr/lib/llvm-21/lib/clang/21/lib/x86_64-pc-linux-gnu/libclang_rt.ubsan_standalone.a:
: No such file or directoryNo such file or directory

/usr/bin/x86_64-linux-gnu-ld.bfd: cannot find
/usr/lib/llvm-21/lib/clang/21/lib/x86_64-pc-linux-gnu/libclang_rt.fuzzer.a:
No such file or directory
/usr/bin/x86_64-linux-gnu-ld.bfd: cannot find
/usr/lib/llvm-21/lib/clang/21/lib/x86_64-pc-linux-gnu/libclang_rt.fuzzer_interceptors.a:
No such file or directory
clang: error: linker command failed with exit code 1 (use -v to see
invocation)
clang: error: linker command failed with exit code 1 (use -v to see
invocation)
make[2]: *** [Makefile:1156:
/packages/tmp/vboot-utils-0~R106-15054.B+dfsg/build/tests/cgpt_fuzzer]
Error 1
make[2]: *** Waiting for unfinished jobs....

So apparently building and shipping Debian's own libFuzzer.a is not good
enough anymore.

Two solutions here:

  - stop building the libfuzzer-N-dev package

  - Ship the libclang_rt.fuzzer.a (and maybe other) libraries.

This is seen with LLVM 21, 22 and 23.

We believe that the bug you reported is fixed in the latest version of
llvm-toolchain-21, which is due to be installed in the Debian FTP archive.

A summary of the changes between this version and the previous one is
attached.

Thank you for reporting the bug, which will now be closed.  If you
have further comments please address them to 1147573@bugs.debian.org,
and the maintainer will reopen the bug report if appropriate.

Debian distribution maintenance software
pp.
Gianfranco Costamagna <locutusofborg@debian.org> (supplier of updated llvm-toolchain-21 package)

(This message was generated automatically at their request; if you
believe that there is a problem with it please contact the archive
administrators by mailing ftpmaster@ftp-master.debian.org)
Format: 1.8
Date: Fri, 28 Aug 2026 11:47:04 +0200
Source: llvm-toolchain-21
Architecture: source
Version: 1:21.1.8-11
Distribution: unstable
Urgency: medium
Maintainer: LLVM Packaging Team <pkg-llvm-team@lists.alioth.debian.org>
Changed-By: Gianfranco Costamagna <locutusofborg@debian.org>
Closes: 1147573
Changes:
 llvm-toolchain-21 (1:21.1.8-11) unstable; urgency=medium
 .
   [ Sylvestre Ledru ]
   * d/rules: only enable sccache if the binary actually runs
   * d/control.in: libfuzzer-X.Y-dev now depends on libclang-rt-X.Y-dev.
     -fsanitize=fuzzer links libclang_rt.fuzzer*.a (and
     libclang_rt.ubsan_standalone.a) from the compiler-rt resource
     directory, which lives in libclang-rt-X.Y-dev. As it was only a
     Recommends of libclang-common-X.Y-dev, it was not pulled into build
     chroots and the link failed. Closes: #1147573.
   * d/tests/fuzzer-test: new autopkgtest building a fuzzer with only
     libfuzzer-X.Y-dev installed, to catch this dependency issue.
   * d/debian-llvm-testsuite.bats: don't skip the libFuzzer compilation test
     when the compiler-rt libraries are missing, fail instead.
 .
   [ Gianfranco Costamagna ]
   * Commit Ubuntu patch to git
   * Skip common packages also for stonking
 .
   [ Karl Smeltzer <karl.smeltzer@canonical.com> ]
   * Add patch from Ubuntu: lldb-python-wrapper-exceptions.diff
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the obsolete libFuzzer.a should be dropped, corresponding patch is on
the 21 branch in the VCS.

Removing the legacy fuzzer.a is a different issue, please open a different bug.
S




Le lundi 14 septembre 2026 à 09:28, Matthias Klose <doko@debian.org> a écrit :

We believe that the bug you reported is fixed in the latest version of
llvm-toolchain-21, which is due to be installed in the Debian FTP archive.

A summary of the changes between this version and the previous one is
attached.

Thank you for reporting the bug, which will now be closed.  If you
have further comments please address them to 1147573@bugs.debian.org,
and the maintainer will reopen the bug report if appropriate.

Debian distribution maintenance software
pp.
Matthias Klose <doko@debian.org> (supplier of updated llvm-toolchain-21 package)

(This message was generated automatically at their request; if you
believe that there is a problem with it please contact the archive
administrators by mailing ftpmaster@ftp-master.debian.org)
Format: 1.8
Date: Mon, 14 Sep 2026 09:20:26 +0200
Source: llvm-toolchain-21
Architecture: source
Version: 1:21.1.8-12
Distribution: unstable
Urgency: medium
Maintainer: LLVM Packaging Team <pkg-llvm-team@lists.alioth.debian.org>
Changed-By: Matthias Klose <doko@debian.org>
Closes: 1147573
Changes:
 llvm-toolchain-21 (1:21.1.8-12) unstable; urgency=medium
 .
   * Stop building, shipping and testing the obsolete libFuzzer.a.
     Closes: #1147573.
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