libstore: Start creating LocalDerivationGoal subclasses

LocalDerivationGoal includes a large number of low-level sandboxing
primitives for Darwin and Linux, intermingled with ifdefs.
Start creating platform-specific classes to make it easier to add new
platforms and review platform-specific code.

This change only creates support infrastructure and moves two function,
more functions will be moved in future changes.

Change-Id: I9fc29fa2a7345107d4fc96c46fa90b4eabf6bb89

9 files changed, 165 insertions, 47 deletions

diff --git a/src/libstore/build/local-derivation-goal.cc b/src/libstore/build/local-derivation-goal.cc
index bae821266..4e616c838 100644
--- a/src/libstore/build/local-derivation-goal.cc
+++ b/src/libstore/build/local-derivation-goal.cc
@@ -51,9 +51,6 @@
 #endif
 
 #if __APPLE__
-#include <spawn.h>
-#include <sys/sysctl.h>
-
 /* This definition is undocumented but depended upon by all major browsers. */
 extern "C" int sandbox_init_with_parameters(const char *profile, uint64_t flags, const char *const parameters[], char **errorbuf);
 #endif
@@ -161,19 +158,7 @@ void LocalDerivationGoal::killChild()
 
 void LocalDerivationGoal::killSandbox(bool getStats)
 {
-    if (cgroup) {
-        #if __linux__
-        auto stats = destroyCgroup(*cgroup);
-        if (getStats) {
-            buildResult.cpuUser = stats.cpuUser;
-            buildResult.cpuSystem = stats.cpuSystem;
-        }
-        #else
-        abort();
-        #endif
-    }
-
-    else if (buildUser) {
+    if (buildUser) {
         auto uid = buildUser->getUID();
         assert(uid != 0);
         killUser(uid);
@@ -2177,31 +2162,8 @@ void LocalDerivationGoal::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") {
-            // Unset kern.curproc_arch_affinity so we can escape Rosetta
-            int affinity = 0;
-            sysctlbyname("kern.curproc_arch_affinity", NULL, NULL, &affinity, sizeof(affinity));
-
-            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, drv->builder.c_str(), NULL, &attrp, stringsToCharPtrs(args).data(), stringsToCharPtrs(envStrs).data());
-#else
-        execve(drv->builder.c_str(), stringsToCharPtrs(args).data(), stringsToCharPtrs(envStrs).data());
-#endif
+        execBuilder(drv->builder, args, envStrs);
+        // execBuilder should not return
 
         throw SysError("executing '%1%'", drv->builder);
 
@@ -2217,6 +2179,11 @@ void LocalDerivationGoal::runChild()
     }
 }
 
+void LocalDerivationGoal::execBuilder(std::string builder, Strings args, Strings envStrs)
+{
+    execve(builder.c_str(), stringsToCharPtrs(args).data(), stringsToCharPtrs(envStrs).data());
+}
+
 
 SingleDrvOutputs LocalDerivationGoal::registerOutputs()
 {
diff --git a/src/libstore/build/local-derivation-goal.hh b/src/libstore/build/local-derivation-goal.hh
index f3a83d42f..91329ca35 100644
--- a/src/libstore/build/local-derivation-goal.hh
+++ b/src/libstore/build/local-derivation-goal.hh
@@ -178,7 +178,28 @@ struct LocalDerivationGoal : public DerivationGoal
 
     friend struct RestrictedStore;
 
-    using DerivationGoal::DerivationGoal;
+    /**
+     * Create a LocalDerivationGoal without an on-disk .drv file,
+     * possibly a platform-specific subclass
+     */
+    static std::shared_ptr<LocalDerivationGoal> makeLocalDerivationGoal(
+        const StorePath & drvPath,
+        const OutputsSpec & wantedOutputs,
+        Worker & worker,
+        BuildMode buildMode
+    );
+
+    /**
+     * Create a LocalDerivationGoal for an on-disk .drv file,
+     * possibly a platform-specific subclass
+     */
+    static std::shared_ptr<LocalDerivationGoal> makeLocalDerivationGoal(
+        const StorePath & drvPath,
+        const BasicDerivation & drv,
+        const OutputsSpec & wantedOutputs,
+        Worker & worker,
+        BuildMode buildMode
+    );
 
     virtual ~LocalDerivationGoal() noexcept(false) override;
 
@@ -282,7 +303,7 @@ struct LocalDerivationGoal : public DerivationGoal
      * Kill any processes running under the build user UID or in the
      * cgroup of the build.
      */
-    void killSandbox(bool getStats);
+    virtual void killSandbox(bool getStats);
 
     /**
      * Create alternative path calculated from but distinct from the
@@ -299,6 +320,16 @@ struct LocalDerivationGoal : public DerivationGoal
      * rewrites caught everything
      */
     StorePath makeFallbackPath(OutputNameView outputName);
+
+protected:
+    using DerivationGoal::DerivationGoal;
+
+    /**
+     * Execute the builder, replacing the current process.
+     * Generally this means an `execve` call.
+     */
+    virtual void execBuilder(std::string builder, Strings args, Strings envStrs);
+
 };
 
 }
diff --git a/src/libstore/build/worker.cc b/src/libstore/build/worker.cc
index 04be0da99..a7a298c34 100644
--- a/src/libstore/build/worker.cc
+++ b/src/libstore/build/worker.cc
@@ -65,8 +65,8 @@ std::shared_ptr<DerivationGoal> Worker::makeDerivationGoal(const StorePath & drv
 {
     return makeDerivationGoalCommon(drvPath, wantedOutputs, [&]() -> std::shared_ptr<DerivationGoal> {
         return !dynamic_cast<LocalStore *>(&store)
-            ? std::make_shared</* */DerivationGoal>(drvPath, wantedOutputs, *this, buildMode)
-            : std::make_shared<LocalDerivationGoal>(drvPath, wantedOutputs, *this, buildMode);
+            ? std::make_shared<DerivationGoal>(drvPath, wantedOutputs, *this, buildMode)
+            : LocalDerivationGoal::makeLocalDerivationGoal(drvPath, wantedOutputs, *this, buildMode);
     });
 }
 
@@ -76,8 +76,8 @@ std::shared_ptr<DerivationGoal> Worker::makeBasicDerivationGoal(const StorePath
 {
     return makeDerivationGoalCommon(drvPath, wantedOutputs, [&]() -> std::shared_ptr<DerivationGoal> {
         return !dynamic_cast<LocalStore *>(&store)
-            ? std::make_shared</* */DerivationGoal>(drvPath, drv, wantedOutputs, *this, buildMode)
-            : std::make_shared<LocalDerivationGoal>(drvPath, drv, wantedOutputs, *this, buildMode);
+            ? std::make_shared<DerivationGoal>(drvPath, drv, wantedOutputs, *this, buildMode)
+            : LocalDerivationGoal::makeLocalDerivationGoal(drvPath, drv, wantedOutputs, *this, buildMode);
     });
 }
 
diff --git a/src/libstore/platform.cc b/src/libstore/platform.cc
index acdedab99..d10d33f0e 100644
--- a/src/libstore/platform.cc
+++ b/src/libstore/platform.cc
@@ -1,4 +1,5 @@
 #include "local-store.hh"
+#include "build/local-derivation-goal.hh"
 
 #if __linux__
 #include "platform/linux.hh"
@@ -19,4 +20,43 @@ std::shared_ptr<LocalStore> LocalStore::makeLocalStore(const Params & params)
     return std::shared_ptr<LocalStore>(new FallbackLocalStore(params));
 #endif
 }
+
+std::shared_ptr<LocalDerivationGoal> LocalDerivationGoal::makeLocalDerivationGoal(
+    const StorePath & drvPath,
+    const OutputsSpec & wantedOutputs,
+    Worker & worker,
+    BuildMode buildMode
+)
+{
+#if __linux__
+    return std::make_shared<LinuxLocalDerivationGoal>(drvPath, wantedOutputs, worker, buildMode);
+#elif __APPLE__
+    return std::make_shared<DarwinLocalDerivationGoal>(drvPath, wantedOutputs, worker, buildMode);
+#else
+    return std::make_shared<FallbackLocalDerivationGoal>(drvPath, wantedOutputs, worker, buildMode);
+#endif
+}
+
+std::shared_ptr<LocalDerivationGoal> LocalDerivationGoal::makeLocalDerivationGoal(
+    const StorePath & drvPath,
+    const BasicDerivation & drv,
+    const OutputsSpec & wantedOutputs,
+    Worker & worker,
+    BuildMode buildMode
+)
+{
+#if __linux__
+    return std::make_shared<LinuxLocalDerivationGoal>(
+        drvPath, drv, wantedOutputs, worker, buildMode
+    );
+#elif __APPLE__
+    return std::make_shared<DarwinLocalDerivationGoal>(
+        drvPath, drv, wantedOutputs, worker, buildMode
+    );
+#else
+    return std::make_shared<FallbackLocalDerivationGoal>(
+        drvPath, drv, wantedOutputs, worker, buildMode
+    );
+#endif
+}
 }
diff --git a/src/libstore/platform/darwin.cc b/src/libstore/platform/darwin.cc
index bbb81784c..83b4b4183 100644
--- a/src/libstore/platform/darwin.cc
+++ b/src/libstore/platform/darwin.cc
@@ -6,6 +6,7 @@
 #include <sys/proc_info.h>
 #include <sys/sysctl.h>
 #include <libproc.h>
+#include <spawn.h>
 
 #include <regex>
 
@@ -220,4 +221,29 @@ void DarwinLocalStore::findPlatformRoots(UncheckedRoots & unchecked)
         }
     }
 }
+
+void DarwinLocalDerivationGoal::execBuilder(std::string builder, Strings args, Strings envStrs)
+{
+    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") {
+        // Unset kern.curproc_arch_affinity so we can escape Rosetta
+        int affinity = 0;
+        sysctlbyname("kern.curproc_arch_affinity", NULL, NULL, &affinity, sizeof(affinity));
+
+        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.c_str(), NULL, &attrp, stringsToCharPtrs(args).data(), stringsToCharPtrs(envStrs).data());
+}
 }
diff --git a/src/libstore/platform/darwin.hh b/src/libstore/platform/darwin.hh
index b7170aa05..0ac7077fb 100644
--- a/src/libstore/platform/darwin.hh
+++ b/src/libstore/platform/darwin.hh
@@ -1,6 +1,7 @@
 #pragma once
 ///@file
 
+#include "build/local-derivation-goal.hh"
 #include "gc-store.hh"
 #include "local-store.hh"
 
@@ -32,4 +33,19 @@ private:
     void findPlatformRoots(UncheckedRoots & unchecked) override;
 };
 
+/**
+ * Darwin-specific implementation of LocalDerivationGoal
+ */
+class DarwinLocalDerivationGoal : public LocalDerivationGoal
+{
+public:
+    using LocalDerivationGoal::LocalDerivationGoal;
+
+private:
+    /**
+     * Set process flags to enter or leave rosetta, then execute the builder
+     */
+    void execBuilder(std::string builder, Strings args, Strings envStrs) override;
+};
+
 }
diff --git a/src/libstore/platform/fallback.hh b/src/libstore/platform/fallback.hh
index fd27edbe6..3b77536bb 100644
--- a/src/libstore/platform/fallback.hh
+++ b/src/libstore/platform/fallback.hh
@@ -1,6 +1,7 @@
 #pragma once
 ///@file
 
+#include "build/local-derivation-goal.hh"
 #include "local-store.hh"
 
 namespace nix {
@@ -28,4 +29,14 @@ public:
     }
 };
 
+/**
+ * Fallback platform implementation of LocalDerivationGoal
+ * Exists so we can make LocalDerivationGoal constructor protected
+ */
+class FallbackLocalDerivationGoal : public LocalDerivationGoal
+{
+public:
+    using LocalDerivationGoal::LocalDerivationGoal;
+};
+
 }
diff --git a/src/libstore/platform/linux.cc b/src/libstore/platform/linux.cc
index a34608894..6b94c01cc 100644
--- a/src/libstore/platform/linux.cc
+++ b/src/libstore/platform/linux.cc
@@ -1,3 +1,4 @@
+#include "cgroup.hh"
 #include "gc-store.hh"
 #include "signals.hh"
 #include "platform/linux.hh"
@@ -114,4 +115,17 @@ void LinuxLocalStore::findPlatformRoots(UncheckedRoots & unchecked)
     readFileRoots("/proc/sys/kernel/fbsplash", unchecked);
     readFileRoots("/proc/sys/kernel/poweroff_cmd", unchecked);
 }
+
+void LinuxLocalDerivationGoal::killSandbox(bool getStats)
+{
+    if (cgroup) {
+        auto stats = destroyCgroup(*cgroup);
+        if (getStats) {
+            buildResult.cpuUser = stats.cpuUser;
+            buildResult.cpuSystem = stats.cpuSystem;
+        }
+    } else {
+        LocalDerivationGoal::killSandbox(getStats);
+    }
+}
 }
diff --git a/src/libstore/platform/linux.hh b/src/libstore/platform/linux.hh
index 8b97e17c5..2cad001ea 100644
--- a/src/libstore/platform/linux.hh
+++ b/src/libstore/platform/linux.hh
@@ -1,6 +1,7 @@
 #pragma once
 ///@file
 
+#include "build/local-derivation-goal.hh"
 #include "gc-store.hh"
 #include "local-store.hh"
 
@@ -32,4 +33,16 @@ private:
     void findPlatformRoots(UncheckedRoots & unchecked) override;
 };
 
+/**
+ * Linux-specific implementation of LocalDerivationGoal
+ */
+class LinuxLocalDerivationGoal : public LocalDerivationGoal
+{
+public:
+    using LocalDerivationGoal::LocalDerivationGoal;
+
+private:
+    void killSandbox(bool getStatus) override;
+};
+
 }