1 files changed, 55 insertions, 9 deletions

diff --git a/src/libutil/util.cc b/src/libutil/util.cc
index 993dc1cb6..885bae69c 100644
--- a/src/libutil/util.cc
+++ b/src/libutil/util.cc
@@ -36,6 +36,7 @@
 #ifdef __linux__
 #include <sys/prctl.h>
 #include <sys/resource.h>
+#include <sys/mman.h>
 
 #include <cmath>
 #endif
@@ -537,6 +538,16 @@ std::string getUserName()
     return name;
 }
 
+Path getHomeOf(uid_t userId)
+{
+    std::vector<char> buf(16384);
+    struct passwd pwbuf;
+    struct passwd * pw;
+    if (getpwuid_r(userId, &pwbuf, buf.data(), buf.size(), &pw) != 0
+        || !pw || !pw->pw_dir || !pw->pw_dir[0])
+        throw Error("cannot determine user's home directory");
+    return pw->pw_dir;
+}
 
 Path getHome()
 {
@@ -558,13 +569,7 @@ Path getHome()
             }
         }
         if (!homeDir) {
-            std::vector<char> buf(16384);
-            struct passwd pwbuf;
-            struct passwd * pw;
-            if (getpwuid_r(geteuid(), &pwbuf, buf.data(), buf.size(), &pw) != 0
-                || !pw || !pw->pw_dir || !pw->pw_dir[0])
-                throw Error("cannot determine user's home directory");
-            homeDir = pw->pw_dir;
+            homeDir = getHomeOf(geteuid());
             if (unownedUserHomeDir.has_value() && unownedUserHomeDir != homeDir) {
                 warn("$HOME ('%s') is not owned by you, falling back to the one defined in the 'passwd' file ('%s')", *unownedUserHomeDir, *homeDir);
             }
@@ -604,6 +609,19 @@ Path getDataDir()
     return dataDir ? *dataDir : getHome() + "/.local/share";
 }
 
+Path getStateDir()
+{
+    auto stateDir = getEnv("XDG_STATE_HOME");
+    return stateDir ? *stateDir : getHome() + "/.local/state";
+}
+
+Path createNixStateDir()
+{
+    Path dir = getStateDir() + "/nix";
+    createDirs(dir);
+    return dir;
+}
+
 
 std::optional<Path> getSelfExe()
 {
@@ -1047,9 +1065,17 @@ static pid_t doFork(bool allowVfork, std::function<void()> fun)
 }
 
 
+static int childEntry(void * arg)
+{
+    auto main = (std::function<void()> *) arg;
+    (*main)();
+    return 1;
+}
+
+
 pid_t startProcess(std::function<void()> fun, const ProcessOptions & options)
 {
-    auto wrapper = [&]() {
+    std::function<void()> wrapper = [&]() {
         if (!options.allowVfork)
             logger = makeSimpleLogger();
         try {
@@ -1069,7 +1095,27 @@ pid_t startProcess(std::function<void()> fun, const ProcessOptions & options)
             _exit(1);
     };
 
-    pid_t pid = doFork(options.allowVfork, wrapper);
+    pid_t pid = -1;
+
+    if (options.cloneFlags) {
+        #ifdef __linux__
+        // Not supported, since then we don't know when to free the stack.
+        assert(!(options.cloneFlags & CLONE_VM));
+
+        size_t stackSize = 1 * 1024 * 1024;
+        auto stack = (char *) mmap(0, stackSize,
+            PROT_WRITE | PROT_READ, MAP_PRIVATE | MAP_ANONYMOUS | MAP_STACK, -1, 0);
+        if (stack == MAP_FAILED) throw SysError("allocating stack");
+
+        Finally freeStack([&]() { munmap(stack, stackSize); });
+
+        pid = clone(childEntry, stack + stackSize, options.cloneFlags | SIGCHLD, &wrapper);
+        #else
+        throw Error("clone flags are only supported on Linux");
+        #endif
+    } else
+        pid = doFork(options.allowVfork, wrapper);
+
     if (pid == -1) throw SysError("unable to fork");
 
     return pid;