Add x86_64-darwin and aarch64 to "extra-platforms" automatically when Rosetta2 is detected#4310
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macOS systems with ARM64 can utilize a translation layer at /Library/Apple/usr/libexec/oah to run x86_64 binaries. This change makes Nix recognize that and it to "extra-platforms". Note that there are two cases here since Nix could be built for either x86_64 or aarch64. In either case, we can switch to the other architecture. Unfortunately there is not a good way to prevent aarch64 binaries from being run in x86_64 contexts or vice versa - programs can always execute programs for the other architecture.
When running universal binaries like /bin/bash, Darwin XNU will choose
which architecture of the binary to use based on "binary preferences".
This change sets that to the current platform for aarch64 and x86_64
builds. In addition it now uses posix_spawn instead of the usual
execve. Note, that this does not prevent the other architecture from
being run, just advises which to use.
Unfortunately, posix_spawnattr_setbinpref_np does not appear to be
inherited by child processes in x86_64 Rosetta 2 translations, meaning
that this will not always work as expected.
For example:
{
arm = derivation {
name = "test";
system = "aarch64-darwin";
builder = "/bin/bash";
args = [ "-e" (builtins.toFile "test" ''
set -x
/usr/sbin/sysctl sysctl.proc_translated
/usr/sbin/sysctl sysctl.proc_native
[ "$(/usr/bin/arch)" = arm64 ]
/usr/bin/touch $out
'') ];
};
rosetta = derivation {
name = "test";
system = "x86_64-darwin";
builder = "/bin/bash";
args = [ "-e" (builtins.toFile "test" ''
set -x
/usr/sbin/sysctl sysctl.proc_translated
/usr/sbin/sysctl sysctl.proc_native
[ "$(/usr/bin/arch)" = i386 ]
echo It works!
/usr/bin/touch $out
'') ];
};
}
`arm' fails on x86_64-compiled Nix, but `arm' and `rosetta' succeed on
aarch64-compiled Nix. I suspect there is a way to fix this since:
$ /usr/bin/arch -arch x86_64 /bin/bash \
-c '/usr/bin/arch -arch arm64e /bin/bash -c /usr/bin/arch'
arm64
seems to work correctly. We may need to wait for Apple to update
system_cmds in opensource.apple.com to find out how though.
matthewbauer
changed the title
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Not sure which bits you're hoping I'll have feedback on; @LnL7 is almost certainly a better mention if he has bandwidth! It's not clear to me exactly what you mean or under what circumstances Rosetta 2 isn't installed or set up (perhaps it would be obvious if I had access to an ARM mac?), but I do still have an intel Big Sur install, so I did run
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I see an unofficial install script for Rosetta 2 that uses the presence of |
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Also, |
Hopefully around Tuesday I can look if that path exists, before installing Rosetta 2 if that helps. |
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What's the state of this one? The path was correct. (Only forgot to confirm it here though) |
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This pull request has been mentioned on NixOS Discourse. There might be relevant details there: |
7 participants
First:
Add extraPlatforms for Rosetta 2 macOS
macOS systems with ARM64 can utilize a translation layer at /Library/Apple/usr/libexec/oah to run x86_64 binaries. This change makes Nix recognize that and it to "extra-platforms". Note that there are two cases here since Nix could be built for either x86_64 or aarch64. In either case, we can switch to the other architecture. Unfortunately there is not a good way to prevent aarch64 binaries from being run in x86_64 contexts or vice versa - programs can always execute programs for the other architecture.
Question: Can someone confirm that /Library/Apple/usr/libexec/oah does not exist when Rosetta 2 is not installed? There could be some stubs there even if Rosetta 2 is not setup yet.Second:
Use posix_spawn_setbinpref_np to advise which architecture to run
When running universal binaries like /bin/bash, Darwin XNU will choose which architecture of the binary to use based on "binary preferences". This change sets that to the current platform for aarch64 and x86_64 builds. In addition it now uses posix_spawn instead of the usual execve. Note, that this does not prevent the other architecture from being run, just advises which to use.
/cc @abathur @thefloweringash @edolstra