kernel+libc: Implement fcntl() for F_DUPFD and F_DUPFD_CLOEXEC

kernel/CMakeLists.txt

@@ -74,8 +74,6 @@ target_link_libraries(moon luna-freestanding)
 
 target_compile_definitions(moon PRIVATE IN_MOON)
 
-target_compile_options(moon PRIVATE -Os)
-
 target_compile_options(moon PRIVATE -Wall -Wextra -Werror -Wvla -Wsign-conversion)
 target_compile_options(moon PRIVATE -Wdisabled-optimization -Wformat=2 -Winit-self)
 target_compile_options(moon PRIVATE -Wmissing-include-dirs -Wswitch-default -Wcast-qual -Wundef) 
@@ -94,6 +92,8 @@ if(MOON_DEBUG_SYMBOLS)
     message(STATUS "Building Moon with debug symbols")
     target_compile_options(moon PRIVATE -ggdb)
     include(debug.cmake)
+else()
+    target_compile_options(moon PRIVATE -Os)
 endif()
 
 target_link_options(moon PRIVATE -lgcc -Wl,--build-id=none -z max-page-size=0x1000 -mcmodel=kernel)

kernel/src/sys/exec.cpp

@@ -6,6 +6,7 @@
 #include "thread/Scheduler.h"
 #include "thread/ThreadImage.h"
 #include <bits/modes.h>
+#include <bits/open-flags.h>
 #include <luna/CString.h>
 #include <luna/ScopeGuard.h>
 #include <luna/Vector.h>
@@ -76,12 +77,16 @@ Result<u64> sys_exec(Registers* regs, SyscallArgs args)
 
     guard.deactivate();
 
-    // FIXME: Close O_CLOEXEC file descriptors.
-    // for (int i = 0; i < FD_MAX; i++) { current->fd_table[i] = {}; }
+    for (int i = 0; i < FD_MAX; i++)
+    {
+        auto& descriptor = current->fd_table[i];
+        if (!descriptor.has_value()) continue;
+        if (descriptor->flags & O_CLOEXEC) descriptor = {};
+    }
 
     MMU::delete_userspace_page_directory(current->directory);
 
-    current->name = argv[0].chars();
+    current->name = path.chars();
 
     image->apply(current);
 

kernel/src/sys/file.cpp

@@ -3,6 +3,8 @@
 #include "memory/MemoryManager.h"
 #include "sys/Syscall.h"
 #include "thread/Scheduler.h"
+#include <bits/fcntl.h>
+#include <bits/open-flags.h>
 #include <bits/seek.h>
 #include <luna/SafeArithmetic.h>
 #include <sys/types.h>
@@ -84,3 +86,33 @@ Result<u64> sys_lseek(Registers*, SyscallArgs args)
 
     return (u64)new_offset;
 }
+
+Result<u64> sys_fcntl(Registers*, SyscallArgs args)
+{
+    int fd = (int)args[0];
+    int cmd = (int)args[1];
+
+    Thread* current = Scheduler::current();
+
+    auto& descriptor = *TRY(current->resolve_fd(fd));
+
+    bool is_cloexec = true;
+
+    switch (cmd)
+    {
+    case F_DUPFD: is_cloexec = false; [[fallthrough]];
+    case F_DUPFD_CLOEXEC: {
+        int arg = (int)args[2];
+        int new_fd = TRY(current->allocate_fd(arg));
+
+        current->fd_table[new_fd] = descriptor;
+
+        if (is_cloexec) current->fd_table[new_fd]->flags |= O_CLOEXEC;
+        else
+            current->fd_table[new_fd]->flags &= ~O_CLOEXEC;
+
+        return (u64)new_fd;
+    }
+    default: return err(EINVAL);
+    }
+}

kernel/src/sys/open.cpp

@@ -7,7 +7,7 @@
 #include <bits/open-flags.h>
 
 // These flags are needed after open(), the rest only affect open().
-constexpr int FLAGS_TO_KEEP = O_RDWR | O_APPEND | O_NONBLOCK;
+constexpr int FLAGS_TO_KEEP = O_RDWR | O_APPEND | O_NONBLOCK | O_CLOEXEC;
 
 Result<u64> sys_open(Registers*, SyscallArgs args)
 {

libc/include/bits/fcntl.h

@@ -0,0 +1,9 @@
+/* bits/fcntl.h: File control flags. */
+
+#ifndef _BITS_FCNTL_H
+#define _BITS_FCNTL_H
+
+#define F_DUPFD 0
+#define F_DUPFD_CLOEXEC 1
+
+#endif

libc/include/bits/open-flags.h

@@ -11,5 +11,6 @@
 #define O_EXCL 16
 #define O_TRUNC 32
 #define O_NONBLOCK 64
+#define O_CLOEXEC 128
 
 #endif

libc/include/fcntl.h

@@ -3,6 +3,7 @@
 #ifndef _FCNTL_H
 #define _FCNTL_H
 
+#include <bits/fcntl.h>
 #include <bits/open-flags.h>
 #include <sys/types.h>
 
@@ -17,6 +18,9 @@ extern "C"
     /* Create a file and return a file descriptor to it. */
     int creat(const char* path, mode_t mode);
 
+    /* Perform a file control operation. */
+    int fcntl(int fd, int cmd, ...);
+
 #ifdef __cplusplus
 }
 #endif

libc/include/unistd.h

@@ -55,6 +55,9 @@ extern "C"
     /* Modify a file descriptor's offset. */
     off_t lseek(int fd, off_t offset, int whence);
 
+    /* Duplicate a file descriptor. */
+    int dup(int fd);
+
 #ifdef __cplusplus
 }
 #endif

libc/src/fcntl.cpp

@@ -23,4 +23,17 @@ extern "C"
     {
         return open(path, O_WRONLY | O_CREAT | O_TRUNC, mode);
     }
+
+    int fcntl(int fd, int cmd, ...)
+    {
+        va_list ap;
+        va_start(ap, cmd);
+
+        uintptr_t arg = (uintptr_t)va_arg(ap, uintptr_t);
+
+        long rc = syscall(SYS_fcntl, fd, cmd, arg);
+
+        va_end(ap);
+        __errno_return(rc, int);
+    }
 }

libc/src/unistd.cpp

@@ -1,4 +1,5 @@
 #include <bits/errno-return.h>
+#include <fcntl.h>
 #include <stdarg.h>
 #include <stdint.h>
 #include <sys/syscall.h>
@@ -83,4 +84,9 @@ extern "C"
         long rc = syscall(SYS_lseek, fd, offset, whence);
         __errno_return(rc, off_t);
     }
+
+    int dup(int fd)
+    {
+        return fcntl(fd, F_DUPFD, 0);
+    }
 }

libluna/include/luna/Syscall.h

@@ -2,7 +2,7 @@
 
 #define enumerate_syscalls(_e)                                                                                         \
     _e(exit) _e(clock_gettime) _e(mmap) _e(munmap) _e(usleep) _e(open) _e(close) _e(read) _e(getpid) _e(write)         \
-        _e(lseek) _e(mkdir) _e(exec) _e(mknod) _e(fork) _e(waitpid) _e(getppid)
+        _e(lseek) _e(mkdir) _e(exec) _e(mknod) _e(fork) _e(waitpid) _e(getppid) _e(fcntl)
 
 enum Syscalls
 {