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

[ryanofsky]

Originally posted by @fanquake in bitcoin/bitcoin#30975 (comment)

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: bitcoin/bitcoin#10102 (comment).
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.

[ryanofsky]

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 #119 could be added to cmake/Config.cmake.in to prevent this

[ryanofsky]

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 3b2617b
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

[ryanofsky]

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