subproc: comments

subproc.c

@@ -298,7 +298,11 @@ static int subprocCloneFunc(void *arg)
 	longjmp(*env_ptr, 1);
 }
 
-// Avoid problem with caching of PID/TID in glibc
+/*
+ * Avoid problems with caching of PID/TID in glibc - when using syscall(__NR_clone) glibc will
+ * not update internal PID/TID caches, which can lead to invalid values returned by getpid(),
+ * or wrong PID/TIDs being used in raise()/abort() functions
+ */
 pid_t subprocClone(uintptr_t flags)
 {
 	if (flags & CLONE_VM) {
@@ -308,11 +312,15 @@ pid_t subprocClone(uintptr_t flags)
 
 	jmp_buf env;
 	if (setjmp(env) == 0) {
-		void *stack_mid = &subprocCloneStack[sizeof(subprocCloneStack) / 2];
-		// Parent
-		return clone(subprocCloneFunc, stack_mid, flags, &env, NULL, NULL);
+		/*
+		 * Avoid the problem of the stack growing up/down under different CPU architectures, by using
+		 * middle of the static stack buffer (which is temporary, and used only inside of subprocCloneFunc
+		 */
+		void *stack = &subprocCloneStack[sizeof(subprocCloneStack) / 2];
+		/* Parent */
+		return clone(subprocCloneFunc, stack, flags, &env, NULL, NULL);
 	}
-	// Child
+	/* Child */
 	return 0;
 }