Treat EACCES for pid_running() as alive

When the user has some sort of hardening going on, we might not be able
to read the Wine process's memory. In that case this check would return
`false` even though the process is still running. To combat this, we
should explicitly check for `EINVAL` which is returned when the file
doesn't exist at all or when it's a broken 'symlink' (even though it
isn't really a symlink).

CHANGELOG.md

@@ -10,6 +10,11 @@ Versioning](https://semver.org/spec/v2.0.0.html).
 
 ### Fixed
 
+- Fixed the process status detection treating a process as dead when the user
+  doesn't have permissions to access the child process's memory. This fixes a
+  seemingly very rare regression from yabridge 3.4.0 where the Wine plugin host
+  application would immediately be seen as dead when using AppArmor, preventing
+  yabridge from starting.
 - Fixed a regression from yabridge 3.4.0 where plugins with zero audio channels
   like FrozenPlain **Obelisk** would result in a crash.
 - Fixed a regression from yabridge 3.4.0 where JUCE-based VST3 plugins might

src/common/utils.cpp

@@ -85,11 +85,16 @@ bool pid_running(pid_t pid) {
     // processes and zombies, and a terminated group host process will always be
     // left as a zombie process. If the process is active, then
     // `/proc/<pid>/{cwd,exe,root}` will be valid symlinks.
-    try {
-        fs::canonical("/proc/" + std::to_string(pid) + "/exe");
-        return true;
-    } catch (const fs::filesystem_error&) {
+    // NOTE: We can get a `EACCES` here if we don't have permissions to read
+    //       this process's memory, so we should explicitly check for `EINVAL`
+    //       indicating that the 'symlink' is broken or just does not exist at
+    //       all.
+    boost::system::error_code err;
+    fs::canonical("/proc/" + std::to_string(pid) + "/exe", err);
+    if (err && err.value() == EINVAL) {
         return false;
+    } else {
+        return true;
     }
 }