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FEATURE: Make the LLVM disassembler an optional runtime dependency #262
Description
Summary
On Fedora 43, installing bpftool pulls in llvm20-libs (~140 MiB) as a hard
dependency, even though the bpftool binary itself is ~730 KiB:
# dnf install bpftool
Installing:
bpftool x86_64 7.6.0-1.fc43 fedora 731.4 KiB
Installing dependencies:
llvm20-filesystem x86_64 20.1.8-2.fc43 fedora 0.0 B
llvm20-libs x86_64 20.1.8-2.fc43 fedora 139.7 MiB
The LLVM library is only used to disassemble JIT-compiled (native) programs,
i.e. bpftool prog dump jited. Every other use case works
without LLVM. For scripting, automation, and CI, dragging in ~140 MB of LLVM
just to have a single optional command available is a heavy cost.
Proposal
Load the LLVM disassembler lazily at runtime via dlopen/dlsym instead of
linking against it at build time. When prog dump jited is invoked and the
library is unavailable, fall back gracefully (libbfd, or an informative message).
This would remove the automatic ELF dependency on libLLVM.so, allowing distributions to make
LLVM a weak/optional dependency (e.g. RPM Recommends) rather than a hard one.
Prior art
The perf tool is solving the exact same problem (libLLVM/libcapstone
bloating dependencies for users who never disassemble) by dlopen-ing these
libraries at runtime, so distributions can ship them as a separate, optional
package:
Alternatives considered
- Build with the libbfd disassembler instead of LLVM (smaller, but a build/
packaging choice and subject to libbfd's unstable ABI). - Build with no disassembler at all (loses
prog dump jitedentirely). - Ship the disassembler in a separate binary (works, but less idiomatic for a
single-binary tool; dlopen keeps the existing UX intact).
Environment
- bpftool 7.6.0-1.fc43 (Fedora 43), x86_64
Activity
[-]FEATURE: Title: Make the LLVM disassembler an optional runtime dependency[/-][+]FEATURE: Make the LLVM disassembler an optional runtime dependency[/+]socketpair commentedon May 30, 2026
A concrete approach:
Move the LLVM disassembler into a small separate
.so(e.g.libbpftool-llvm.so)that links libLLVM normally, and
dlopenit only whenprog dump jitedneeds it. The main binary then has no link-time dependency on libLLVM.The split follows the existing interface in
jit_disasm.c:disasm_init(),init_context(),disassemble_insn(),destroy_context()go into the .so;disasm_print_insn()stays in the binary and drives the loop/JSON formatting.qmonnet commentedon Jun 1, 2026
Thanks for the suggestion. I'm not opposed to it, although we probably want to keep the disassembler built-in when libbfd is used. Do you plan to work on this?
bpftool: Move LLVM functionality into plugin (fixes libbpf#262)
socketpair commentedon Jun 1, 2026
@qmonnet Please review the PR
mirror: bpftool: Move LLVM functionality into plugin (fixes libbpf#262)
mirror: bpftool: Move LLVM functionality into plugin (fixes libbpf#262)
mirror: bpftool: Move LLVM functionality into plugin (fixes libbpf#262)
mirror: bpftool: Move LLVM functionality into plugin (fixes libbpf#262)
mirror: bpftool: Move LLVM functionality into plugin (fixes libbpf#262)
socketpair commentedon Jun 3, 2026
https://lore.kernel.org/bpf/20260603-bpftool-plugin-v1-1-68c0ac91f5a3@gmail.com/T/#u
bpftool: Make the LLVM disassembler an optional runtime dependency
bpftool: Make the LLVM disassembler an optional runtime dependency
bpftool: Make the LLVM disassembler an optional runtime dependency
7 remaining items
bpftool: Make the LLVM disassembler an optional runtime dependency
bpftool: Make the LLVM disassembler an optional runtime dependency
bpftool: Make the LLVM disassembler an optional runtime dependency
bpftool: Make the LLVM disassembler an optional runtime dependency
bpftool: Make the LLVM disassembler an optional runtime dependency
bpftool: Make the LLVM disassembler an optional runtime dependency
bpftool: Make the LLVM disassembler an optional runtime dependency
bpftool: Make the LLVM disassembler an optional runtime dependency
bpftool: Make the LLVM disassembler an optional runtime dependency
bpftool: Make the LLVM disassembler an optional runtime dependency
bpftool: Make the LLVM disassembler an optional runtime dependency
bpftool: Make the LLVM disassembler an optional runtime dependency
bpftool: Make the LLVM disassembler an optional runtime dependency
bpftool: Make the LLVM disassembler an optional runtime dependency
bpftool: Make the LLVM disassembler an optional runtime dependency