diff options
Diffstat (limited to 'lib/systems/parse.nix')
| -rw-r--r-- | lib/systems/parse.nix | 23 |
1 files changed, 14 insertions, 9 deletions
diff --git a/lib/systems/parse.nix b/lib/systems/parse.nix index a06ac0d11f7..accaeb652d0 100644 --- a/lib/systems/parse.nix +++ b/lib/systems/parse.nix @@ -121,15 +121,20 @@ rec { js = { bits = 32; significantByte = littleEndian; family = "js"; }; }; - # Determine where two CPUs are compatible with each other. That is, - # can we run code built for system b on system a? For that to - # happen, then the set of all possible possible programs that system - # b accepts must be a subset of the set of all programs that system - # a accepts. This compatibility relation forms a category where each - # CPU is an object and each arrow from a to b represents - # compatibility. CPUs with multiple modes of Endianness are - # isomorphic while all CPUs are endomorphic because any program - # built for a CPU can run on that CPU. + # Determine when two CPUs are compatible with each other. That is, + # can code built for system B run on system A? For that to happen, + # the programs that system B accepts must be a subset of the + # programs that system A accepts. + # + # We have the following properties of the compatibility relation, + # which must be preserved when adding compatibility information for + # additional CPUs. + # - (reflexivity) + # Every CPU is compatible with itself. + # - (transitivity) + # If A is compatible with B and B is compatible with C then A is compatible with C. + # - (compatible under multiple endianness) + # CPUs with multiple modes of endianness are pairwise compatible. isCompatible = a: b: with cpuTypes; lib.any lib.id [ # x86 (b == i386 && isCompatible a i486) |