Build error "libatomic not found" on Ubuntu LTS release (24.04) #132

Originally posted by @fanquake in https://github.com/bitcoin/bitcoin/issues/30975#issuecomment-2610191420

Basic usage of building libmultiprocess yourself, on the current Ubuntu LTS release (24.04), for use with Core, doesn't currently work:

<libmultiprocess compiled & installed following instructions>
cmake -B build -DWITH_MULTIPROCESS=ON
-- The CXX compiler identification is GNU 13.3.0
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Found SQLite3: /usr/include (found suitable version "3.45.1", minimum required is "3.7.17") 
-- Looking for __atomic_load_8 in atomic
-- Looking for __atomic_load_8 in atomic - not found
CMake Error at /usr/lib/aarch64-linux-gnu/cmake/CapnProto/CapnProtoConfig.cmake:108 (message):
  libatomic not found
Call Stack (most recent call first):
  /usr/share/cmake-3.28/Modules/CMakeFindDependencyMacro.cmake:76 (find_package)
  /usr/local/lib/cmake/Libmultiprocess/LibmultiprocessConfig.cmake:38 (find_dependency)
  CMakeLists.txt:146 (find_package)

-- Configuring incomplete, errors occurred!

Having to work around this was also mentioned here: https://github.com/bitcoin/bitcoin/pull/10102#issuecomment-2515554249. We can likely work around this ourselves, but something this basic should be fixed before requiring developers to use this library. Along with reporting & upstreaming fixes to what are now new (hard) dependencies for us.

To clarify, this error does not happen when running libmultiprocess cmake configuration, but when running another cmake configuration that that calls find_package(Libmultiprocess REQUIRED COMPONENTS Lib). Probably the workaround from https://github.com/chaincodelabs/libmultiprocess/pull/119 could be added to cmake/Config.cmake.in to prevent this

I tried to reproduce this and couldn't. Then I realized I accidentally downloaded ubuntu 22.04 not 24.04. Good to know that this issue does not seem to happen with 22.04 though!

/etc/os-release is VERSION="22.04.5 LTS (Jammy Jellyfish)" libmultiprocess is 3b2617b3e59f55ae3501c82a62c87f393077779f bitcoin commit is d5a2ba44ba4f23fcf3b3408d28438b7c7013ba36

lxc launch ubuntu:jammy ubu
lxc image list images:  | grep -i ubuntu
lxc exec ubu -- /bin/bash
lxc exec ubu -- adduser --shell /bin/bash --ingroup sudo ubu
lxc exec ubu -- su - ubu

git clone https://github.com/bitcoin/bitcoin
git clone https://github.com/chaincodelabs/libmultiprocess
sudo apt update
sudo apt-get install build-essential cmake pkg-config python3 libevent-dev libboost-dev libsqlite3-dev libcapnp-dev capnproto cmake-curses-gui

cd ~/libmultiprocess
mkdir build
cd build
cmake ..
make
make check # Optionally build and run tests
sudo make install

cd ~/bitcoin
cmake -B build
ccmake build # toggle WITH_MULTIPROCESS
make -j12 -C build bitcoin-node bitcoin-cli

build/src/bitcoin-node -ipcbind=unix:cool -regtes
build/src/bitcoin-cli -regtest echoipc hi

Was able to reproduce this problem with steps above just replacing jammy with noble and using ubuntu VERSION="24.04.1 LTS (Noble Numbat)"

Confirmed that applying #133 fixes it