On Thu, 20 Jun 2019 at 16:19, Kacvinsky, Tom <Tom.Kacvinsky@xxxxxxxxxx> wrote: > > Hi, > > I have built a 32-bit GCC 8.3.0 (no multi-lib support) on RHEL 5 and a 64-bit GCC 8.3.0 > (again, no multi-lib support) on CentOS 5.11. What I find interesting is that when I go > to compile a program that will need atomic locks (a Boost template class pulled in via > a header file), the 32-bit object code requires the library -latomic, but 64-bit object > code does not require that. > > Looking over "info gcc" I see a multitude of options for atomic operations. The take > away for me sis that for architectures that have an instruction set that has support > for atomic operations, libatomic is not necessary, but for other architectures, it is. Right. Sort of. It depends what kind of variables you're using the atomic operations with. libatomic can still be needed on x86_64, but only for types larger than 64-bits. On i386 you need libatomic even for 32-bit integers, as it has no atomic operations. i586 has 64-bit atomics though. So if you configured your 32-bit compiler for i386, not i586 or later, then by default it will want to use libatomic for all atomic ops.
