Gentoo Linux Installation Guide (Advanced Optimization)

COMMON_FLAGS="-march=native -O2 -pipe"
CFLAGS="${COMMON_FLAGS}"
CXXFLAGS="${COMMON_FLAGS}"
FCFLAGS="${COMMON_FLAGS}"   # Fortran
FFLAGS="${COMMON_FLAGS}"    # Fortran 77

MAKEOPTS="-j<core count> -l<load limit>"
EMERGE_DEFAULT_OPTS="--jobs=<parallel packages> --load-average=<load>"

# Basic USE examples
USE="systemd dbus policykit"
USE="${USE} wayland X gtk qt6"
USE="${USE} pipewire pulseaudio alsa"
USE="${USE} -doc -test"

L10N="en en-US"
LINGUAS="en en_US"

# GPU
VIDEO_CARDS="nvidia"        # NVIDIA
# VIDEO_CARDS="amdgpu"      # AMD
# VIDEO_CARDS="intel"       # Intel
# Input devices
INPUT_DEVICES="libinput"
# CPU features (auto-detect, run: emerge --ask app-portage/cpuid2cpuflags)
CPU_FLAGS_X86="<cpuid2cpuflags output>"

FEATURES="parallel-fetch parallel-install candy ccache"

# /etc/portage/make.conf
COMMON_FLAGS="-march=native -O2 -pipe"
CFLAGS="${COMMON_FLAGS}"
CXXFLAGS="${COMMON_FLAGS}"
MAKEOPTS="-j8"  # Adjust to CPU thread count
USE="systemd wayland pipewire -doc -test"
L10N="en en-US"
VIDEO_CARDS="intel"  # or nvidia/amdgpu
FEATURES="parallel-fetch candy"
ACCEPT_LICENSE="*"

emerge --sync              # Sync software repository
emerge -avuDN @world       # Update all software

eselect news list          # List news
eselect news read          # Read news

dispatch-conf              # Interactive config file merge (recommended)
# or
etc-update

emerge --ask --depclean    # Remove orphaned dependencies no longer needed

emerge --ask app-portage/gentoolkit # Install toolkit
eclean-dist                         # Clean downloaded old source packages

glsa-check -l      # List all unresolved security advisories
glsa-check -t all  # Test all affected packages

emerge --ask dev-build/ccache
ccache -M 20G  # Set cache size to 20GB

www-client/firefox lto pgo
www-client/chromium lto pgo  # Note: PGO may not work under Wayland

# Enable globally in /etc/portage/make.conf
USE="lto"

CFLAGS="${CFLAGS} -flto"
CXXFLAGS="${CXXFLAGS} -flto"

www-client/firefox lto.conf
app-editors/vim lto.conf

# These warnings indicate runtime issues LTO may cause, elevate them to errors
# -Werror=odr: One Definition Rule violation (multiple definitions of the same symbol)
# -Werror=lto-type-mismatch: LTO type mismatch
# -Werror=strict-aliasing: Strict aliasing violation
WARNING_FLAGS="-Werror=odr -Werror=lto-type-mismatch -Werror=strict-aliasing"

# -O2: Optimization level 2 (recommended)
# -pipe: Use pipes to speed up compilation
# -march=native: Optimize for the current CPU
# -flto: Enable Link Time Optimization (Full LTO)
# Note: GCC's -flto defaults to Full LTO, suitable for GCC systems
COMMON_FLAGS="-O2 -pipe -march=native -flto ${WARNING_FLAGS}"

CFLAGS="${COMMON_FLAGS}"          # C compiler flags
CXXFLAGS="${COMMON_FLAGS}"        # C++ compiler flags
FCFLAGS="${COMMON_FLAGS}"         # Fortran compiler flags
FFLAGS="${COMMON_FLAGS}"          # Fortran 77 compiler flags

LDFLAGS="${COMMON_FLAGS} ${LDFLAGS}"  # Linker flags

USE="lto"  # USE flag to enable LTO support

# Clang has not fully implemented these diagnostics yet, but keep them for future use
# -Werror=odr: One Definition Rule violation detection (partially supported in Clang)
# -Werror=strict-aliasing: Strict aliasing violation detection (in development for Clang)
WARNING_FLAGS="-Werror=odr -Werror=strict-aliasing"

# -O2: Optimization level 2 (balances performance and stability)
# -pipe: Use pipes to speed up compilation
# -march=native: Optimize for the current CPU
# -flto=thin: Enable ThinLTO (recommended, faster and parallelized)
COMMON_FLAGS="-O2 -pipe -march=native -flto=thin ${WARNING_FLAGS}"

CFLAGS="${COMMON_FLAGS}"          # C compiler flags
CXXFLAGS="${COMMON_FLAGS}"        # C++ compiler flags
FCFLAGS="${COMMON_FLAGS}"         # Fortran compiler flags
FFLAGS="${COMMON_FLAGS}"          # Fortran 77 compiler flags

LDFLAGS="${COMMON_FLAGS} ${LDFLAGS}"  # Linker flags

USE="lto"  # USE flag to enable LTO support

# Add to /etc/portage/make.conf
RUSTFLAGS="${RUSTFLAGS} -Clinker-plugin-lto"

# Common flags with Clang optimization and ThinLTO
WARNING_FLAGS="-Werror=odr -Werror=strict-aliasing"
COMMON_FLAGS="-march=native -O2 -flto=thin -pipe ${WARNING_FLAGS}"
CFLAGS="${COMMON_FLAGS}"          # C flags
CXXFLAGS="${COMMON_FLAGS}"        # C++ flags
FCFLAGS="${COMMON_FLAGS}"         # Fortran flags
FFLAGS="${COMMON_FLAGS}"          # Fortran 77 flags

# Rust compiler flags
RUSTFLAGS="-C target-cpu=native -C strip=debuginfo -C opt-level=3 \
-Clinker=clang -Clinker-plugin-lto -Clink-arg=-fuse-ld=lld"

# Linker flags pointing to LLD
LDFLAGS="${COMMON_FLAGS} ${LDFLAGS} -fuse-ld=lld"

# Compiler explicit definitions
CC="clang"
CXX="clang++"
CPP="clang-cpp"
AR="llvm-ar"
NM="llvm-nm"
RANLIB="llvm-ranlib"
USE="lto"

dev-lang/rust llvm-lto.conf

emerge --ask llvm-core/clang llvm-core/lld

CC="clang"
CXX="clang++"
CPP="clang-cpp"  # Some packages (e.g., xorg-server) need this
AR="llvm-ar"
NM="llvm-nm"
RANLIB="llvm-ranlib"

app-editors/neovim clang.conf

emerge --ask llvm-core/clang-runtime
emerge --ask llvm-runtimes/compiler-rt-sanitizers

llvm-core/clang-runtime sanitize
llvm-runtimes/compiler-rt-sanitizers profile orc

CC="clang"
CXX="clang++"
CPP="clang-cpp"
AR="llvm-ar"
NM="llvm-nm"
RANLIB="llvm-ranlib"

CC="gcc"
CXX="g++"
CPP="gcc -E"
AR="ar"
NM="nm"
RANLIB="ranlib"

sys-libs/glibc gcc.conf
app-emulation/wine gcc.conf

# Install kernel sources and build tools
emerge --ask sys-kernel/gentoo-sources
# (Optional) Install Genkernel for automation
emerge --ask sys-kernel/genkernel
# (Optional) Required for LLVM/Clang compilation
emerge --ask llvm-core/llvm \
    llvm-core/clang llvm-core/lld

lscpu  # View CPU model, core count, architecture, etc.
cat /proc/cpuinfo | grep "model name" | head -1  # CPU model

lspci -k  # List all PCI devices and their current drivers
lspci | grep -i vga  # View GPU
lspci | grep -i network  # View network card

lsusb  # List all USB devices

lsmod  # List all currently loaded modules
lsmod | wc -l  # Module count

cd /usr/src/linux
# Method 1: Create minimal config based on currently loaded modules
make localmodconfig
# This only enables kernel options for currently loaded modules (strongly recommended!)
# Method 2: Create config based on currently running kernel
zcat /proc/config.gz > .config  # If current kernel supports it
make olddefconfig  # Update config using default values

cd /usr/src/linux
make menuconfig  # Text interface (recommended)

  ┌────────────── Linux/x86 6.17.9-gentoo Kernel Configuration ──────────────┐
  │  Arrow keys navigate the menu.  <Enter> selects submenus ---> (or empty  │  
  │  submenus ----).  Highlighted letters are hotkeys.  Pressing <Y>         │  
  │  includes, <N> excludes, <M> modularizes features.  Press <Esc><Esc> to  │  
  │  exit, <?> for Help, </> for Search.  Legend: [*] built-in  [ ] excluded │  
  │ ┌──────────────────────────────────────────────────────────────────────┐ │  
  │ │        General setup  --->                                           │ │  
  │ │    [*] 64-bit kernel                                                 │ │  
  │ │        Processor type and features  --->                             │ │  
  │ │    [ ] Mitigations for CPU vulnerabilities  ----                     │ │  
  │ │        Power management and ACPI options  --->                       │ │  
  │ │        Bus options (PCI etc.)  --->                                  │ │  
  │ │        Binary Emulations  --->                                       │ │  
  │ │    [*] Virtualization  --->                                          │ │  
  │ │        General architecture-dependent options  --->                  │ │  
  │ │    [*] Enable loadable module support  --->                          │ │  
  │ │    -*- Enable the block layer  --->                                  │ │  
  │ │        Executable file formats  --->                                 │ │  
  │ │        Memory Management options  --->                               │ │  
  │ │    -*- Networking support  --->                                      │ │  
  │ │        Device Drivers  --->                                          │ │  
  │ │        File systems  --->                                            │ │  
  │ │        Security options  --->                                        │ │  
  │ │        Cryptographic API  --->                                       │ │  
  │ │        Library routines  --->                                        │ │  
  │ │    [ ] Kernel hacking  ----                                          │ │  
  │ └───────────────────────────────────────────────────────────────────────v│  
  ├──────────────────────────────────────────────────────────────────────────┤  
  │          <Select>    < Exit >    < Help >    < Save >    < Load >        │  
  └──────────────────────────────────────────────────────────────────────────┘  

cd /usr/src/linux
# Use Genkernel's default config (includes most hardware support)
genkernel --kernel-config=/usr/share/genkernel/arch/x86_64/kernel-config all
# Or use the distribution default config as a base
make defconfig  # Kernel default config
# Then adjust as needed
make menuconfig

cd /usr/src/linux
# Compile with Clang
make LLVM=1 -j$(nproc)
# Compile with Clang + LTO (recommended)
make LLVM=1 LLVM_IAS=1 -j$(nproc)

KERNEL_CC="clang"
KERNEL_LD="ld.lld"

General setup
  → Compiler optimization level → Optimize for performance  # Select -O2 (recommended)
  → Link Time Optimization (LTO) → Clang ThinLTO (NEW)      # Enable ThinLTO (strongly recommended)

cd /usr/src/linux
# Compile kernel and modules
make -j$(nproc)         # Use all CPU cores
make modules_install    # Install modules to /lib/modules/
make install            # Install kernel to /boot/
# (Optional) Using LLVM/Clang + LTO
make LLVM=1 -j$(nproc)
make LLVM=1 modules_install
make LLVM=1 install

# Basic usage
genkernel --install all
# Using LLVM/Clang
genkernel --kernel-cc=clang --utils-cc=clang --install all
# Enable LTO (requires manual .config configuration)
genkernel --kernel-make-opts="LLVM=1" --install all

cd /usr/src/linux
echo "=== Kernel Stats ==="
echo "Built-in: $(grep -c '=y$' .config)"
echo "Modules: $(grep -c '=m$' .config)"
echo "Total configs: $(wc -l < .config)"
echo "Kernel size: $(ls -lh arch/x86/boot/bzImage 2>/dev/null | awk '{print $5}')"
echo "Compression: $(grep '^CONFIG_KERNEL_' .config | grep '=y' | sed 's/CONFIG_KERNEL_//;s/=y//')"

=== Kernel Stats ===
Built-in: 1723
Modules: 201
Total configs: 6687
Kernel size: 11M
Compression: ZSTD

Device Drivers  --->
    <*> Multiple devices driver support (RAID and LVM)
        <*> RAID support
            [*] Autodetect RAID arrays during kernel boot
            # Choose based on your RAID level (must select Y):
            <*> Linear (append) mode
            <*> RAID-0 (striping) mode
            <*> RAID-1 (mirroring) mode
            <*> RAID-10 (mirrored striping) mode
            <*> RAID-4/RAID-5/RAID-6 mode