From 743aedcd495fadd583846426a417b6c5d9699ec0 Mon Sep 17 00:00:00 2001
From: apio <blobs.trading@gmail.com>
Date: Wed, 12 Oct 2022 20:41:55 +0200
Subject: [PATCH] libc: Implement atexit() and _exit()

exit() now calls registered handlers before calling _exit().

And initialize_libc() can now register a handler to close stdout and stderr on program termination!! :)
---
 libs/libc/include/stdlib.h |  6 +++---
 libs/libc/include/unistd.h |  4 ++++
 libs/libc/src/atexit.cpp   | 25 +++++++++++++++++++++++++
 libs/libc/src/init.cpp     |  7 +++++++
 libs/libc/src/stdlib.cpp   | 13 +------------
 libs/libc/src/unistd.cpp   |  6 ++++++
 6 files changed, 46 insertions(+), 15 deletions(-)
 create mode 100644 libs/libc/src/atexit.cpp

diff --git a/libs/libc/include/stdlib.h b/libs/libc/include/stdlib.h
index f8380026..cde4fa34 100644
--- a/libs/libc/include/stdlib.h
+++ b/libs/libc/include/stdlib.h
@@ -12,11 +12,11 @@ extern "C"
     /* Aborts the program. */
     noreturn void abort();
 
-    /* Exits the program with the specified status code. */
+    /* Normally exits the program with the specified status code. */
     noreturn void exit(int status);
 
-    /* Not implemented. */
-    int atexit(void (*)(void));
+    /* Registers a handler function to be run at normal program termination. */
+    int atexit(void (*handler)(void));
 
     /* Not implemented.*/
     int atoi(const char*);
diff --git a/libs/libc/include/unistd.h b/libs/libc/include/unistd.h
index 871b3646..f86abe77 100644
--- a/libs/libc/include/unistd.h
+++ b/libs/libc/include/unistd.h
@@ -1,6 +1,7 @@
 #ifndef _UNISTD_H
 #define _UNISTD_H
 
+#include <bits/macros.h>
 #include <bits/seek.h>
 #include <sys/types.h>
 
@@ -20,6 +21,9 @@ extern "C"
     /* Not implemented. */
     pid_t fork(void);
 
+    /* Terminates the program with the status code status. */
+    noreturn void _exit(int status);
+
     /* Calls the kernel for a specific service, determined by number. */
     long syscall(long number, ...);
 
diff --git a/libs/libc/src/atexit.cpp b/libs/libc/src/atexit.cpp
new file mode 100644
index 00000000..8df2a117
--- /dev/null
+++ b/libs/libc/src/atexit.cpp
@@ -0,0 +1,25 @@
+#include <stdlib.h>
+#include <unistd.h>
+
+#define ATEXIT_MAX_FUNCS 32
+
+typedef void (*atexit_func_t)(void);
+
+atexit_func_t atexit_functions[ATEXIT_MAX_FUNCS];
+int atexit_function_count = 0;
+
+extern "C"
+{
+    int atexit(atexit_func_t handler)
+    {
+        if (atexit_function_count >= ATEXIT_MAX_FUNCS) return -1;
+        atexit_functions[atexit_function_count++] = handler;
+        return 0;
+    }
+
+    noreturn void exit(int status)
+    {
+        for (int i = 0; i < atexit_function_count; i++) { atexit_functions[i](); }
+        _exit(status);
+    }
+}
\ No newline at end of file
diff --git a/libs/libc/src/init.cpp b/libs/libc/src/init.cpp
index c77def4e..24df6f78 100644
--- a/libs/libc/src/init.cpp
+++ b/libs/libc/src/init.cpp
@@ -4,6 +4,12 @@
 #include <stdlib.h>
 #include <unistd.h>
 
+static void terminate_libc()
+{
+    fclose(stdout);
+    fclose(stderr);
+}
+
 extern "C" void initialize_libc()
 {
     if (lseek(0, 0, SEEK_CUR) < 0)
@@ -24,4 +30,5 @@ extern "C" void initialize_libc()
         errno = 0;
     }
     else { stderr = fdopen(1, "rw"); }
+    atexit(terminate_libc);
 }
\ No newline at end of file
diff --git a/libs/libc/src/stdlib.cpp b/libs/libc/src/stdlib.cpp
index 9841f6de..f05cf891 100644
--- a/libs/libc/src/stdlib.cpp
+++ b/libs/libc/src/stdlib.cpp
@@ -7,18 +7,7 @@ extern "C"
 {
     noreturn void abort()
     {
-        exit(-1);
-    }
-
-    noreturn void exit(int status)
-    {
-        syscall(SYS_exit, status);
-        __builtin_unreachable();
-    }
-
-    int atexit(void (*)(void))
-    {
-        NOT_IMPLEMENTED("atexit");
+        _exit(-1);
     }
 
     int atoi(const char*)
diff --git a/libs/libc/src/unistd.cpp b/libs/libc/src/unistd.cpp
index 8b1da12e..21efc6ea 100644
--- a/libs/libc/src/unistd.cpp
+++ b/libs/libc/src/unistd.cpp
@@ -95,4 +95,10 @@ extern "C"
     {
         return syscall(SYS_seek, fd, offset, whence);
     }
+
+    noreturn void _exit(int status)
+    {
+        syscall(SYS_exit, status);
+        __builtin_unreachable();
+    }
 }
\ No newline at end of file