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Use posix_spawn_setbinpref_np to advise which architecture to run

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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.
This commit is contained in:
Matthew Bauer 2020-12-03 15:41:59 -06:00
parent 9b1824ecbd
commit 4b9acf4e21
1 changed files with 24 additions and 0 deletions
Download patch file Download diff file Expand all files Collapse all files

24
src/libstore/build/derivation-goal.cc
View file

@ -50,6 +50,10 @@
#define pivot_root(new_root, put_old) (syscall(SYS_pivot_root, new_root, put_old))
#endif
#if __APPLE__
#include <spawn.h>
#endif
#include <pwd.h>
#include <grp.h>
@ -2844,7 +2848,27 @@ void DerivationGoal::runChild()
}
}
#if __APPLE__
posix_spawnattr_t attrp;
if (posix_spawnattr_init(&attrp))
throw SysError("failed to initialize builder");
if (posix_spawnattr_setflags(&attrp, POSIX_SPAWN_SETEXEC))
throw SysError("failed to initialize builder");
if (drv->platform == "aarch64-darwin") {
cpu_type_t cpu = CPU_TYPE_ARM64;
posix_spawnattr_setbinpref_np(&attrp, 1, &cpu, NULL);
} else if (drv->platform == "x86_64-darwin") {
cpu_type_t cpu = CPU_TYPE_X86_64;
posix_spawnattr_setbinpref_np(&attrp, 1, &cpu, NULL);
}
posix_spawn(NULL, builder, NULL, &attrp, stringsToCharPtrs(args).data(), stringsToCharPtrs(envStrs).data());
#else
execve(builder, stringsToCharPtrs(args).data(), stringsToCharPtrs(envStrs).data());
#endif
throw SysError("executing '%1%'", drv->builder);