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systemd/docs/PORTING_TO_NEW_ARCHITECTURES.md
Jason A. Donenfeld ffa047a03e random-util: remove RDRAND usage 
/dev/urandom is seeded with RDRAND. Calling genuine_random_bytes(...,
..., 0) will use /dev/urandom as a last resort. Hence, we gain nothing
here by having our own RDRAND wrapper, because /dev/urandom already is
based on RDRAND output, even before /dev/urandom has fully initialized.

Furthermore, RDRAND is not actually fast! And on each successive
generation of new x86 CPUs, from both AMD and Intel, it just gets
slower.

This commit simplifies things by just using /dev/urandom in cases where
we before might use RDRAND, since /dev/urandom will always have RDRAND
mixed in as part of it.

And above where I say "/dev/urandom", what I actually mean is
GRND_INSECURE, which is the same thing but won't generate warnings in
dmesg.
2022-03-14 19:47:13 +00:00

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title category layout SPDX-License-Identifier
Porting to New Architectures Contributing default LGPL-2.1-or-later

Porting systemd to New Architectures

Here's a brief checklist of things to implement when porting systemd to a new architecture.

  1. Patch src/basic/architecture.h and src/basic/architecture.c to make your architecture known to systemd. Besides an ARCHITECTURE_XYZ enumeration entry you need to provide an implementation of native_architecture() and uname_architecture().

  2. Patch src/shared/gpt.h and src/shared/gpt.c and define a new set of GPT partition type UUIDs for the root file system, /usr/ file system, and the matching Verity and Verity signature partitions. Use systemd-id128 new -p to generate new suitable UUIDs you can use for this. Make sure to register your new types in the various functions in gpt.c. Also make sure to update the tables in docs/DISCOVERABLE_PARTITIONS.md and man/systemd-gpt-auto-generator.xml accordingly.

  3. If your architecture supports UEFI, make sure to update the efi_arch variable logic in meson.build to be set to the right architecture string as defined by the UEFI specification. (This ensures that systemd-boot will be built as the appropriately named BOOT<arch>.EFI binary.) Also, if your architecture uses a special boot protocol for the Linux kernel make sure to implement it in src/boot/efi/linux*.c, so that the systemd-stub EFI stub can work.

  4. Make sure to register the right system call numbers for your architecture in src/basic/missing_syscall_def.h. systemd uses various system calls the Linux kernel provides that are currently not wrapped by glibc (or are only in very new glibc), and we need to know the right numbers for them. It might also be necessary to tweak src/basic/raw-clone.h.

  5. Make sure the code in src/shared/seccomp-util.c properly understands the local architecture and its system call quirks.

  6. If your architecture uses a /lib64/ library directory, then make sure that the BaseFilesystem table in src/shared/base-filesystem.c has an entry for it so that it can be set up automatically if missing. This is useful to support booting into OS trees that have an empty root directory with only /usr/ mounted in.

  7. If your architecture supports VM virtualization and provides CPU opcodes similar to x86' CPUID consider adding native support for detecting VMs this way to src/basic/virt.c.