“Glibc with LSE” refers to the version of the GNU C Library (glibc) that includes support for LSE (Large Systems Extensions) . LSE is an extension to the ARMv8-A architecture that provides enhanced atomic operations and memory model features.
LSE introduces additional atomic instructions and operations, such as Load-Acquire, Store-Release, and Atomic Compare-and-Swap (CAS). These operations allow for more efficient synchronization and concurrent access to shared memory in multi-threaded applications running on ARMv8-A processors.
When glibc is compiled with LSE support, it can take advantage of these enhanced atomic operations provided by the LSE extension. This can potentially improve the performance of multi-threaded applications that heavily rely on atomic operations and synchronization primitives.
If you have a recent version of Linux, you probably do not need to change your GNU C Library.
Your version of the GNU C Library may already have support for LSE. Before you build a new version check if LSE is already included by running:
objdump -d /lib/aarch64-linux-gnu/libc.so.6 | grep -i 'cas\|casp\|swp\|ldadd\|stadd\|ldclr\|stclr\|ldeor\|steor\|ldset\|stset\|ldsmax\|stsmax\|ldsmin\|stsmin\|ldumax\|stumin' | wc -l
If a non-zero number is printed your GNU C Library already has LSE.
Most recent Linux distributions, including Ubuntu 22.04 and Ubuntu 24.04, already have LSE included in the GNU C Library.
Launch an Arm based instance running Ubuntu version 20.04.
On your machine, install the dependencies required to build glibc:
sudo apt update
sudo apt install -y gcc-10 g++-10 gawk bison make
Incorrectly modifying the GNU C Library on your system may result in failing applications or complete system failure. You should use a temporary virtual machine which can be deleted if problems occur.
You can now checkout the glibc source package and create a build directory:
cd ~
git clone https://sourceware.org/git/glibc.git
cd glibc
git checkout glibc-2.32
build=~/glibc-2.32_build_install/build
mkdir -p $build
cd $build
Configure glibc and run make to build it:
sudo bash ~/glibc/configure --prefix=/usr --disable-werror CC=gcc-10 CXX=g++-10
sudo make -C $build -j$(expr $(nproc) - 1)
You have now successfully built glibc from source without LSE.
Now lets look at how you can build it with LSE support.
To build glibc with LSE, you should add CFLAGS and CXXFLAGS to the configure command.
You can do this one of two ways. One way is to use “-mcpu=native” which tells the compiler to detect the architecture/micro-architecture of your machine. The other way is to pass the exact architecture option of your machine to the compiler using “-mcpu=neoverse-n2+lse”.
Both ways are shown below:
sudo bash ~/glibc/configure --prefix=/usr --disable-werror CC=gcc-10 CXX=g++-10 CFLAGS="-mcpu=native -O3" CXXFLAGS="-mcpu=native -O3"
sudo make -C $build -j$(expr $(nproc) - 1)
OR
sudo bash ~/glibc/configure --prefix=/usr --disable-werror CC=gcc-10 CXX=g++-10 CFLAGS="-mcpu=neoverse-n2+lse -O3" CXXFLAGS="-mcpu=neoverse-n2+lse -O3"
sudo make -C $build -j$(expr $(nproc) - 1)
After running make, you should see glibc (libc.so.6) with LSE support in your build directory.