gc: Start libproc-based Darwin roots

src/libstore/gc.cc

@@ -1,6 +1,7 @@
 #include "derivations.hh"
 #include "globals.hh"
 #include "local-store.hh"
+#include "logging.hh"
 #include "signals.hh"
 #include "finally.hh"
 
@@ -21,6 +22,11 @@
 #include <sys/un.h>
 #include <unistd.h>
 
+#ifdef __APPLE__
+#include <sys/proc_info.h>
+#include <libproc.h>
+#endif
+
 namespace nix {
 
 
@@ -357,12 +363,9 @@ static void readFileRoots(const char * path, UncheckedRoots & roots)
             throw;
     }
 }
-#endif
 
-void LocalStore::findRuntimeRoots(Roots & roots, bool censor)
+static void readProcfsRoots(const Path & storeDir, UncheckedRoots & unchecked)
 {
-    UncheckedRoots unchecked;
-
     auto procDir = AutoCloseDir{opendir("/proc")};
     if (procDir) {
         struct dirent * ent;
@@ -418,8 +421,99 @@ void LocalStore::findRuntimeRoots(Roots & roots, bool censor)
         if (errno)
             throw SysError("iterating /proc");
     }
+}
+#endif
 
-#if !defined(__linux__)
+#ifdef __APPLE__
+static void readLibprocRoots(const Path & storeDir, UncheckedRoots & unchecked)
+{
+    int pidBufSize = proc_listpids(PROC_ALL_PIDS, 0, nullptr, 0);
+    if (pidBufSize <= 0 || pidBufSize % sizeof(int) != 0)
+        throw SysError("Listing PIDs");
+
+    std::vector<int> pids(pidBufSize / sizeof(int));
+    pidBufSize = proc_listpids(PROC_ALL_PIDS, 0, pids.data(), pidBufSize);
+    if (pidBufSize <= 0 || pidBufSize % sizeof(int) != 0)
+        throw SysError("Listing PIDs");
+    pids.resize(pidBufSize / sizeof(int));
+
+    for (auto pid: pids) {
+        // It doesn't make sense to ask about the kernel
+        if (pid == 0)
+            continue;
+
+        // Process cwd/root directory
+        struct proc_vnodepathinfo vnodeInfo;
+        if (proc_pidinfo(pid, PROC_PIDVNODEPATHINFO, 0, &vnodeInfo, sizeof(vnodeInfo)) <= 0) {
+            if (errno == ESRCH) continue;
+            throw SysError("Getting PID info");
+        };
+        unchecked[std::string(vnodeInfo.pvi_cdir.vip_path)].emplace("{libproc/cwd}");
+        unchecked[std::string(vnodeInfo.pvi_rdir.vip_path)].emplace("{libproc/rootdir}");
+
+        // File descriptors
+        int fdBufSize = proc_pidinfo(pid, PROC_PIDLISTFDS, 0, nullptr, 0);
+        if (fdBufSize <= 0 || fdBufSize % sizeof(struct proc_fdinfo) != 0)
+            throw SysError("Listing PID's file descriptors");
+        std::vector<struct proc_fdinfo> fds(fdBufSize / sizeof(struct proc_fdinfo));
+        fdBufSize = proc_pidinfo(pid, PROC_PIDLISTFDS, 0, fds.data(), fdBufSize);
+        if (fdBufSize <= 0)
+            throw SysError("Listing PID's file descriptors");
+        fds.resize(fdBufSize / sizeof(struct proc_fdinfo));
+        for (auto fd: fds) {
+            // While there are names for other FD types, only vnodes are in the filesystem
+            if (fd.proc_fdtype != PROX_FDTYPE_VNODE)
+                continue;
+
+            struct vnode_fdinfowithpath fdInfo;
+            if (proc_pidfdinfo(pid, fd.proc_fd, PROC_PIDFDVNODEPATHINFO, &fdInfo, sizeof(fdInfo)) <= 0)
+                throw SysError("Getting file descriptor path");
+
+            unchecked[std::string(fdInfo.pvip.vip_path)].emplace("{libproc/fd}");
+        }
+
+        // Regions (e.g. mmapped files, executables, shared libraries)
+        struct proc_regionwithpathinfo regionInfo;
+        uint64_t nextAddr = 0;
+        while (true) {
+            // Seriously, what are you doing XNU?
+            // There's 3 flavors of PROC_PIDREGIONPATHINFO:
+            // * PROC_PIDREGIONPATHINFO includes all regions
+            // * PROC_PIDREGIONPATHINFO2 includes regions backed by a vnode
+            // * PROC_PIDREGIONPATHINFO3 includes regions backed by a vnode on a specified filesystem
+            // Only PROC_PIDREGIONPATHINFO is documented.
+            // Unfortunately, using it would make finding gcroots take about 50x as long
+            // and tests would fail from timeout.
+            // According to the Frida source code, PROC_PIDREGIONPATHINFO2 has been available
+            // since XNU 2782.1.97 in OS X 10.10
+            //
+            // This is PROC_PIDREGIONPATHINFO2
+            if (proc_pidinfo(pid, 22, nextAddr, &regionInfo, sizeof(regionInfo)) <= 0) {
+                if ((errno == ESRCH) || (errno == EINVAL))
+                    break;
+                throw SysError("Getting region path");
+            }
+
+            unchecked[std::string(regionInfo.prp_vip.vip_path)].emplace("{libproc/region}");
+
+            nextAddr = regionInfo.prp_prinfo.pri_address + regionInfo.prp_prinfo.pri_size;
+        }
+
+        // TODO: per-thread cwds (apparently exist but I don't see them much)
+
+    }
+}
+#endif
+
+void LocalStore::findRuntimeRoots(Roots & roots, bool censor)
+{
+    UncheckedRoots unchecked;
+
+#ifdef __APPLE__
+    readLibprocRoots(storeDir, unchecked);
+#elif defined(__linux__)
+    readProcfsRoots(storeDir, unchecked);
+#else
     try {
         std::regex lsofRegex(R"(^n(/.*)$)");
         auto lsofLines =