no need separate /boot partition for BIOS on qemu EFI requires extra work to configure on qemu, BIOS is enough

/etc/portage/make.conf

#------------------------------------------------------------------------------
# CPU & optimization flags
#------------------------------------------------------------------------------
# march=znver4      → tune for AMD Zen 4 (Ryzen 7000 series)
# O2                → safe optimization level
# pipe              → use pipes rather than temp files
# fstack-protector-strong → lightweight stack smashing protection
# fomit-frame-pointer    → omit frame pointers for a bit more speed
COMMON_FLAGS="-march=native -O2 -pipe -fstack-protector-strong -fomit-frame-pointer"
CFLAGS="${COMMON_FLAGS}"
CXXFLAGS="${COMMON_FLAGS}"
FCFLAGS="${COMMON_FLAGS}"
FFLAGS="${COMMON_FLAGS}"
MAKEOPTS="-j31 -l16"

ABI_X86="64"
LC_MESSAGES=C.utf8

ACCEPT_KEYWORDS="amd64"
ACCEPT_LICENSE="*"

# qemu uses BIOS by default, EFI requires extra configuration.
GRUB_PLATFORMS="pc"

# Check active USE flags with `emerge --info`.
USE="$USE udev"
USE="$USE -bindist -ipv6 -libtirpc -man -multilib -systemd -test-rust -wayland -X"

GENTOO_MIRRORS="https://mirror.rackspace.com/gentoo/"

things to consider in the kernel configuration ARCH=x86_64 make defconfig

• General setup
  • Default hostname
  • Kernel .config support
  • Initial RAM filesystem and RAM disk (initramfs/initrd) support
  • Profiling support
• Processor type and features
  • Disable either everything Intel or everything AMD
  • Support for extended (non-PC) x86 platforms
  • Linux guest support
  • EFI runtime service support
• Power management and ACPI options
  • Suspend to RAM and standby
  • Hibernation (aka 'suspend to disk')
• Binary Emulations
  • IA32 Emulation
• Virtualization
• Enable loadable module support
• Networking support
  • Networking options
    • The IPv6 protocol
  • Wireless to disable you must disable the driver first
• Device Drivers
  • PCCard (PCMCIA/CardBus) support
  • Misc devices
  • SCSI device support disable everything you can
  • Serial ATA and Parallel ATA drivers (libata)
  • Multiple devices driver support (RAID and LVM)
  • Macintosh device drivers
  • Network device support
    • Virtio network driver this is enough for qemu, dont need the ethernet one
    • Ethernet driver support
    • USB Network Adapters
    • Wireless LAN
  • Input device support
    • Mouse interface
    • Joystick interface
    • Keyboards you can disable this if you only ssh but keyboard stops working in the vm directly
    • Mice
    • Joysticks/Gamepads
    • Tablets
    • Touchscreens
    • Miscellaneous devices
    • Graphics support
    • Sound card support
    • HID bus support
    • USB support
    • Microsoft Surface Platform-Specific Device Drivers
    • X86 Platform Specific Device Drivers
    • IOMMU Hardware Support
  • File systems
    • Enable the necesary ones like ext4, btrfs as needed
    • CD-ROM/DVD Filesystems
    • DOS/FAT/EXFAT/NT Filesystems
    • Pseudo filesystems give a check here
    • Miscellaneous filesystems
    • Network File Systems
  • Kernel hacking
    • Kernel debugging
    • Generic Kernel Debugging Instruments
      • Magic SysRq key
      • Debug Filesystem
    • Tracers
    • Remote debugging over FireWire early on boot

/etc/default/grub

GRUB_TIMEOUT_STYLE=hidden
GRUB_TIMEOUT=0
GRUB_HIDDEN_TIMEOUT=0
GRUB_HIDDEN_TIMEOUT_QUIET=true

/etc/inittab

comment all unneeded

# TERMINALS
#x1:12345:respawn:/sbin/agetty 38400 console linux
c1:12345:respawn:/sbin/agetty --noclear 38400 tty1 linux
#c2:2345:respawn:/sbin/agetty 38400 tty2 linux
#c3:2345:respawn:/sbin/agetty 38400 tty3 linux
#c4:2345:respawn:/sbin/agetty 38400 tty4 linux
#c5:2345:respawn:/sbin/agetty 38400 tty5 linux
#c6:2345:respawn:/sbin/agetty 38400 tty6 linux