Implement fork()!

This is quite cool! The syscall entry point plumbs the register dump
down to sys$fork(), which uses it to set up the child process's TSS
in order to resume execution right after the int 0x80 fork() call. :^)

This works pretty well, although there is some problem with the kernel
alias mappings used to clone the parent process's regions. If I disable
the MM::release_page_directory() code, there's no problem. Probably there's
a premature freeing of a physical page somehow.

1 files changed, 12 insertions, 0 deletions

diff --git a/Userland/sh.cpp b/Userland/sh.cpp
index 524658e27f..6efa9ce4de 100644
--- a/Userland/sh.cpp
+++ b/Userland/sh.cpp
@@ -32,6 +32,13 @@ static int sh_pwd(int, const char**)
     return 0;
 }
 
+static int sh_fork(int, const char**)
+{
+    pid_t pid = fork();
+    printf("getpid()=%d, fork()=%d\n", getpid(), pid);
+    return 0;
+}
+
 static int sh_exit(int, const char**)
 {
     printf("Good-bye!\n");
@@ -94,6 +101,11 @@ static bool handle_builtin(int argc, const char** argv, int& retval)
         retval = sh_exit(argc, argv);
         return true;
     }
+
+    if (!strcmp(argv[0], "fork")) {
+        retval = sh_fork(argc, argv);
+        return true;
+    }
     return false;
 }