Kernel/LibC/Networking: Be able to send UDP messages

Now it can send UDP messages to a specific IP address and libc has
enough to create a basic UDP ECHO server, that is kinda cool.

19 files changed, 269 insertions, 45 deletions

diff --git a/Makefile b/Makefile
index ed7c933..0218376 100644
--- a/Makefile
+++ b/Makefile
@@ -1,6 +1,6 @@
 CC="./sysroot/bin/i686-sb-gcc"
 AS="./sysroot/bin/i686-sb-as"
-OBJ = arch/i386/boot.o init/kernel.o cpu/gdt.o cpu/reload_gdt.o cpu/idt.o cpu/io.o libc/stdio/print.o drivers/keyboard.o log.o drivers/pit.o libc/string/memcpy.o libc/string/strlen.o libc/string/memcmp.o drivers/ata.o libc/string/memset.o cpu/syscall.o  read_eip.o libc/exit/assert.o process.o cpu/int_syscall.o libc/string/strcpy.o arch/i386/mmu.o kmalloc.o fs/ext2.o fs/vfs.o fs/devfs.o cpu/spinlock.o random.o libc/string/strcmp.o crypto/ChaCha20/chacha20.o crypto/SHA1/sha1.o fs/tmpfs.o libc/string/isequal.o drivers/pst.o halts.o scalls/ppoll.o scalls/ftruncate.o kubsan.o scalls/mmap.o drivers/serial.o scalls/accept.o scalls/bind.o scalls/socket.o socket.o poll.o fs/fifo.o hashmap/hashmap.o fs/shm.o scalls/shm.o elf.o ksbrk.o sched/scheduler.o scalls/stat.o libc/string/copy.o libc/string/strncpy.o drivers/mouse.o libc/string/strlcpy.o libc/string/strcat.o drivers/vbe.o scalls/msleep.o scalls/uptime.o scalls/mkdir.o drivers/pci.o drivers/rtl8139.o network/ethernet.o network/arp.o network/bytes.o network/ipv4.o network/udp.o scalls/recvfrom.o math.o
+OBJ = arch/i386/boot.o init/kernel.o cpu/gdt.o cpu/reload_gdt.o cpu/idt.o cpu/io.o libc/stdio/print.o drivers/keyboard.o log.o drivers/pit.o libc/string/memcpy.o libc/string/strlen.o libc/string/memcmp.o drivers/ata.o libc/string/memset.o cpu/syscall.o  read_eip.o libc/exit/assert.o process.o cpu/int_syscall.o libc/string/strcpy.o arch/i386/mmu.o kmalloc.o fs/ext2.o fs/vfs.o fs/devfs.o cpu/spinlock.o random.o libc/string/strcmp.o crypto/ChaCha20/chacha20.o crypto/SHA1/sha1.o fs/tmpfs.o libc/string/isequal.o drivers/pst.o halts.o scalls/ppoll.o scalls/ftruncate.o kubsan.o scalls/mmap.o drivers/serial.o scalls/accept.o scalls/bind.o scalls/socket.o socket.o poll.o fs/fifo.o hashmap/hashmap.o fs/shm.o scalls/shm.o elf.o ksbrk.o sched/scheduler.o scalls/stat.o libc/string/copy.o libc/string/strncpy.o drivers/mouse.o libc/string/strlcpy.o libc/string/strcat.o drivers/vbe.o scalls/msleep.o scalls/uptime.o scalls/mkdir.o drivers/pci.o drivers/rtl8139.o network/ethernet.o network/arp.o network/bytes.o network/ipv4.o network/udp.o scalls/recvfrom.o math.o scalls/sendto.o
 CFLAGS = -O2 -fsanitize=vla-bound,shift-exponent,pointer-overflow,shift,signed-integer-overflow,bounds -ggdb -ffreestanding -Wall -Werror -mgeneral-regs-only -Wimplicit-fallthrough -I./libc/include/ -I.
 INCLUDE=-I./includes/ -I./libc/include/
 
@@ -23,7 +23,7 @@ nk:
 	qemu-system-i386 -d int -netdev user,id=n0,hostfwd=udp:127.0.0.1:6001-:6000 -device rtl8139,netdev=n0 -no-reboot -no-shutdown -serial file:./serial.log -hda ext2.img -m 1G -cdrom myos.iso -s
 
 run:
-	qemu-system-i386 -enable-kvm -netdev user,id=n0,hostfwd=udp:127.0.0.1:6001-:6000 -device rtl8139,netdev=n0 -d int -no-reboot -no-shutdown -chardev stdio,id=char0,logfile=serial.log,signal=off -serial chardev:char0 -hda ext2.img -m 1G -cdrom myos.iso -s
+	qemu-system-i386 -enable-kvm -netdev user,id=n0,hostfwd=udp:127.0.0.1:6001-:6000 -device rtl8139,netdev=n0 -object filter-dump,id=id,netdev=n0,file=netout -d int -no-reboot -no-shutdown -chardev stdio,id=char0,logfile=serial.log,signal=off -serial chardev:char0 -hda ext2.img -m 1G -cdrom myos.iso -s
 
 myos.iso: myos.bin
 	cp myos.bin isodir/boot
diff --git a/cpu/syscall.c b/cpu/syscall.c
index 6ad5514..9bf5075 100644
--- a/cpu/syscall.c
+++ b/cpu/syscall.c
@@ -15,6 +15,7 @@
 #include <scalls/msleep.h>
 #include <scalls/ppoll.h>
 #include <scalls/recvfrom.h>
+#include <scalls/sendto.h>
 #include <scalls/shm.h>
 #include <scalls/socket.h>
 #include <scalls/stat.h>
@@ -162,8 +163,8 @@ void (*syscall_functions[])() = {
     (void(*))syscall_socket,    (void(*))syscall_shm_open,
     (void(*))syscall_ftruncate, (void(*))syscall_stat,
     (void(*))syscall_msleep,    (void(*))syscall_uptime,
-    (void(*))syscall_mkdir,
-    (void(*))syscall_recvfrom,
+    (void(*))syscall_mkdir,     (void(*))syscall_recvfrom,
+    (void(*))syscall_sendto,
 };
 
 void syscall_function_handler(uint32_t eax, uint32_t arg1, uint32_t arg2,
diff --git a/drivers/rtl8139.c b/drivers/rtl8139.c
index 02a5159..3853eab 100644
--- a/drivers/rtl8139.c
+++ b/drivers/rtl8139.c
@@ -4,6 +4,7 @@
 #include <drivers/pci.h>
 #include <drivers/rtl8139.h>
 #include <mmu.h>
+#include <network/arp.h>
 #include <network/ethernet.h>
 
 #define RBSTART 0x30
diff --git a/network/arp.c b/network/arp.c
index f86c732..de6d898 100644
--- a/network/arp.c
+++ b/network/arp.c
@@ -20,9 +20,28 @@ struct ARP_DATA {
                     // above). If IPv4 can just be a "u32" type.
 };
 
+struct ARP_TABLE_ENTRY {
+  uint8_t is_used;
+  uint8_t mac[6];
+  uint8_t ip[4];
+};
+
+struct ARP_TABLE_ENTRY arp_table[10] = {0};
+
 // FIXME: This is hardcoded, don't do this.
 uint8_t ip_address[4] = {10, 0, 2, 15};
 
+struct ARP_TABLE_ENTRY *find_arp_entry_to_use(void) {
+  // This does not need to find a "free" entry as a ARP table is
+  // just a cache, it just has to pick a entry efficently.
+  for (int i = 0; i < 10; i++) {
+    if (!arp_table[i].is_used) {
+      return &arp_table[i];
+    }
+  }
+  return &arp_table[0];
+}
+
 void print_mac(const char *str, uint8_t *mac) {
   kprintf("%s: ", str);
   for (int i = 0; i < 6; i++) {
@@ -33,7 +52,7 @@ void print_mac(const char *str, uint8_t *mac) {
   kprintf("\n");
 }
 
-void print_ip(const char *str, uint8_t *ip) {
+void print_ip(const char *str, const uint8_t *ip) {
   kprintf("%s: ", str);
   for (int i = 0; i < 4; i++) {
     kprintf("%d", ip[i]);
@@ -43,42 +62,92 @@ void print_ip(const char *str, uint8_t *ip) {
   kprintf("\n");
 }
 
+void send_arp_request(const uint8_t ip[4]) {
+  struct ARP_DATA data;
+  data.htype = htons(1);
+  data.ptype = htons(0x0800);
+
+  data.hlen = 6;
+  data.plen = 4;
+
+  data.opcode = htons(0x0001);
+  get_mac_address(data.srchw);
+  memcpy(data.srcpr, ip_address, sizeof(uint8_t[4]));
+
+  memset(data.dsthw, 0, sizeof(uint8_t[6]));
+  memcpy(data.dstpr, ip, sizeof(uint8_t[4]));
+
+  uint8_t broadcast[6];
+  memset(broadcast, 0xFF, sizeof(broadcast));
+  send_ethernet_packet(broadcast, 0x0806, (uint8_t *)&data, sizeof(data));
+}
+
+int get_mac_from_ip(const uint8_t ip[4], uint8_t mac[6]) {
+  print_ip("ARP GETTING MAC FROM IP: ", ip);
+  for (int i = 0; i < 10; i++) {
+    if (0 != memcmp(arp_table[i].ip, ip, sizeof(uint8_t[4])))
+      continue;
+    memcpy(mac, arp_table[i].mac, sizeof(uint8_t[6]));
+    return 1;
+  }
+  klog("ARP cache miss", LOG_NOTE);
+  asm("sti");
+  send_arp_request(ip);
+  // TODO: Maybe wait a bit?
+  for (int i = 0; i < 10; i++) {
+    if (0 != memcmp(arp_table[i].ip, ip, sizeof(uint8_t[4])))
+      continue;
+    memcpy(mac, arp_table[i].mac, sizeof(uint8_t[6]));
+    return 1;
+  }
+  assert(0);
+  return 0;
+}
+
 void handle_arp(const uint8_t *payload) {
   struct ARP_DATA *data = (struct ARP_DATA *)payload;
 
   // Assert that communication is over ethernet
   assert(1 == ntohs(data->htype));
-  // Assert it is a request
-  assert(0x0001 == ntohs(data->opcode));
   // Assert that request uses IP
   assert(0x0800 == ntohs(data->ptype));
 
   assert(6 == data->hlen);
   assert(4 == data->plen);
-  print_mac("srchw: ", data->srchw);
-  print_ip("srcpr: ", data->srcpr);
+  // Assert it is a request
+  if (0x0001 /*arp_request*/ == ntohs(data->opcode)) {
+    print_mac("srchw: ", data->srchw);
+    print_ip("srcpr: ", data->srcpr);
 
-  print_mac("dsthw: ", data->dsthw);
-  print_ip("dstpr: ", data->dstpr);
+    print_mac("dsthw: ", data->dsthw);
+    print_ip("dstpr: ", data->dstpr);
 
-  uint8_t mac[6];
-  get_mac_address(mac);
-  print_mac("THIS DEVICE MAC: ", mac);
-  assert(0 == memcmp(data->dstpr, ip_address, sizeof(uint8_t[4])));
-
-  // Now we have to construct a ARP response
-  struct ARP_DATA response;
-  response.htype = htons(1);
-  response.ptype = htons(0x0800);
-  response.opcode = htons(0x00002);
-  response.hlen = 6;
-  response.plen = 4;
-  get_mac_address(response.srchw);
-  memcpy(response.srcpr, ip_address, sizeof(uint8_t[4]));
-
-  memcpy(response.dsthw, data->srchw, sizeof(uint8_t[6]));
-  memcpy(response.dstpr, data->srcpr, sizeof(uint8_t[4]));
-
-  send_ethernet_packet(data->srchw, 0x0806, (uint8_t *)&response,
-                       sizeof(response));
+    assert(0 == memcmp(data->dstpr, ip_address, sizeof(uint8_t[4])));
+
+    // Now we have to construct a ARP response
+    struct ARP_DATA response;
+    response.htype = htons(1);
+    response.ptype = htons(0x0800);
+    response.opcode = htons(0x00002);
+    response.hlen = 6;
+    response.plen = 4;
+    get_mac_address(response.srchw);
+    memcpy(response.srcpr, ip_address, sizeof(uint8_t[4]));
+
+    memcpy(response.dsthw, data->srchw, sizeof(uint8_t[6]));
+    memcpy(response.dstpr, data->srcpr, sizeof(uint8_t[4]));
+
+    send_ethernet_packet(data->srchw, 0x0806, (uint8_t *)&response,
+                         sizeof(response));
+  } else if (0x0002 /*arp_response*/ == ntohs(data->opcode)) {
+    // Find a entry to fill
+    struct ARP_TABLE_ENTRY *entry = find_arp_entry_to_use();
+    entry->is_used = 1;
+    memcpy(entry->mac, data->srchw, sizeof(uint8_t[6]));
+    memcpy(entry->ip, data->srcpr, sizeof(uint8_t[4]));
+    print_ip("Added ip: ", entry->ip);
+  } else {
+    kprintf("GOT A ARP REQEUST WITH TYPE: %x\n", ntohs(data->opcode));
+    assert(0);
+  }
 }
diff --git a/network/arp.h b/network/arp.h
index 8efda97..c2beb94 100644
--- a/network/arp.h
+++ b/network/arp.h
@@ -1,3 +1,4 @@
 #include <stdint.h>
 
+int get_mac_from_ip(const uint8_t ip[4], uint8_t mac[6]);
 void handle_arp(const uint8_t *payload);
diff --git a/network/ethernet.c b/network/ethernet.c
index 11a3876..e97ccbd 100644
--- a/network/ethernet.c
+++ b/network/ethernet.c
@@ -55,17 +55,7 @@ void handle_ethernet(const uint8_t *packet, uint64_t packet_length) {
   kprintf("OUR OWN CALCULATED crc: %x\n",
           crc32((const char *)eth_header, (packet_length - 4)));
 
-  kprintf("mac dst: ");
-  for (int i = 0; i < 6; i++)
-    kprintf("%x", eth_header->mac_dst[i]);
-  kprintf("\n");
-  kprintf("mac src: ");
-  for (int i = 0; i < 6; i++)
-    kprintf("%x", eth_header->mac_src[i]);
-  kprintf("\n");
-
   uint16_t type = ntohs(eth_header->type);
-  kprintf("Etheretype: %x\n", type);
   switch (type) {
   case 0x0806:
     handle_arp(payload);
diff --git a/network/ipv4.c b/network/ipv4.c
index e7ef2c2..099aa0d 100644
--- a/network/ipv4.c
+++ b/network/ipv4.c
@@ -1,11 +1,78 @@
 #include <assert.h>
+#include <kmalloc.h>
+#include <network/arp.h>
 #include <network/bytes.h>
+#include <network/ethernet.h>
 #include <network/ipv4.h>
 #include <network/udp.h>
 #include <string.h>
 
+uint16_t ip_checksum(void *vdata, size_t length) {
+  // Cast the data pointer to one that can be indexed.
+  char *data = (char *)vdata;
+
+  // Initialise the accumulator.
+  uint32_t acc = 0xffff;
+
+  // Handle complete 16-bit blocks.
+  for (size_t i = 0; i + 1 < length; i += 2) {
+    uint16_t word;
+    memcpy(&word, data + i, 2);
+    acc += ntohs(word);
+    if (acc > 0xffff) {
+      acc -= 0xffff;
+    }
+  }
+
+  // Handle any partial block at the end of the data.
+  if (length & 1) {
+    uint16_t word = 0;
+    memcpy(&word, data + length - 1, 1);
+    acc += ntohs(word);
+    if (acc > 0xffff) {
+      acc -= 0xffff;
+    }
+  }
+
+  // Return the checksum in network byte order.
+  return htons(~acc);
+}
+
+extern uint8_t ip_address[4];
+void send_ipv4_packet(uint32_t ip, uint8_t protocol, const uint8_t *payload,
+                      uint16_t length) {
+  uint8_t header[20] = {0};
+  header[0] = (4 /*version*/ << 4) | (5 /*IHL*/);
+  *((uint16_t *)(header + 2)) = htons(length + 20);
+  header[8 /*TTL*/] = 0xF8;
+  header[9] = protocol;
+
+  memcpy(header + 12 /*src_ip*/, ip_address, sizeof(uint8_t[4]));
+  memcpy(header + 16, &ip, sizeof(uint8_t[4]));
+
+  *((uint16_t *)(header + 10 /*checksum*/)) = ip_checksum(header, 20);
+  uint16_t packet_length = length + 20;
+  uint8_t *packet = kmalloc(packet_length);
+  memcpy(packet, header, 20);
+  memcpy(packet + 20, payload, length);
+
+  uint8_t mac[6];
+  uint8_t ip_copy[4]; // TODO: Do I need to do this?
+  memcpy(ip_copy, &ip, sizeof(uint8_t[4]));
+  get_mac_from_ip(ip_copy, mac);
+  send_ethernet_packet(mac, 0x0800, packet, packet_length);
+  kfree(packet);
+}
+
 void handle_ipv4(const uint8_t *payload, uint32_t packet_length) {
   assert(packet_length > 4);
+
+  uint16_t saved_checksum = *(uint16_t *)(payload + 10);
+  *(uint16_t *)(payload + 10) = 0;
+  uint16_t calc_checksum = ip_checksum((uint8_t *)payload, 20);
+  *(uint16_t *)(payload + 10) = saved_checksum;
+  assert(calc_checksum == saved_checksum);
+
   uint8_t version = (*payload & 0xF0) >> 4;
   uint8_t IHL = (*payload & 0xF);
   kprintf("version: %x\n", version);
diff --git a/network/ipv4.h b/network/ipv4.h
index 294a0ef..f578202 100644
--- a/network/ipv4.h
+++ b/network/ipv4.h
@@ -1,3 +1,5 @@
 #include <stdint.h>
 
 void handle_ipv4(const uint8_t *payload, uint32_t packet_length);
+void send_ipv4_packet(uint32_t ip, uint8_t protocol, const uint8_t *payload,
+                      uint16_t length);
diff --git a/network/udp.c b/network/udp.c
index 29f17e1..23411da 100644
--- a/network/udp.c
+++ b/network/udp.c
@@ -1,8 +1,24 @@
 #include <assert.h>
 #include <network/bytes.h>
+#include <network/ipv4.h>
 #include <network/udp.h>
 #include <socket.h>
 
+void send_udp_packet(struct sockaddr_in *src, const struct sockaddr_in *dst,
+                     const uint8_t *payload, uint16_t payload_length) {
+  uint16_t header[4] = {0};
+  header[0] = src->sin_port;
+  header[1] = dst->sin_port;
+  header[2] = htons(payload_length + 8);
+
+  uint16_t packet_length = sizeof(header) + payload_length;
+  uint8_t *packet = kmalloc(packet_length);
+  memcpy(packet, header, sizeof(header));
+  memcpy(packet + sizeof(header), payload, payload_length);
+  send_ipv4_packet(dst->sin_addr.s_addr, 0x11, packet, packet_length);
+  kfree(packet);
+}
+
 void handle_udp(uint8_t src_ip[4], const uint8_t *payload,
                 uint32_t packet_length) {
   assert(packet_length >= 8);
@@ -10,11 +26,10 @@ void handle_udp(uint8_t src_ip[4], const uint8_t *payload,
   // h_.* means host format((probably) little endian)
   uint16_t n_source_port = *(uint16_t *)payload;
   uint16_t h_source_port = ntohs(n_source_port);
+  (void)h_source_port;
   uint16_t h_dst_port = ntohs(*(uint16_t *)(payload + 2));
   uint16_t h_length = ntohs(*(uint16_t *)(payload + 4));
   assert(h_length == packet_length);
-  kprintf("source_port: %d\n", h_source_port);
-  kprintf("dst_port: %d\n", h_dst_port);
   uint16_t data_length = h_length - 8;
   const uint8_t *data = payload + 8;
 
diff --git a/network/udp.h b/network/udp.h
index 8278b87..c30b8c8 100644
--- a/network/udp.h
+++ b/network/udp.h
@@ -1,3 +1,7 @@
+#include <socket.h>
 #include <stdint.h>
 
-void handle_udp(uint8_t src_ip[4], const uint8_t *payload, uint32_t packet_length);
+void handle_udp(uint8_t src_ip[4], const uint8_t *payload,
+                uint32_t packet_length);
+void send_udp_packet(struct sockaddr_in *src, const struct sockaddr_in *dst,
+                     const uint8_t *payload, uint16_t payload_length);
diff --git a/scalls/sendto.c b/scalls/sendto.c
new file mode 100644
index 0000000..48c4020
--- /dev/null
+++ b/scalls/sendto.c
@@ -0,0 +1,23 @@
+#include <assert.h>
+#include <network/bytes.h>
+#include <network/udp.h>
+#include <scalls/sendto.h>
+
+size_t syscall_sendto(int socket, const void *message, size_t length,
+           int flags, struct t_two_args *extra_args /*
+	   const struct sockaddr *dest_addr,
+           socklen_t dest_len*/) {
+  const struct sockaddr *dest_addr = (const struct sockaddr *)extra_args->a;
+  socklen_t dest_len = (socklen_t)extra_args->b;
+  (void)dest_len;
+  vfs_fd_t *fd = get_vfs_fd(socket);
+  assert(fd);
+  SOCKET *s = (SOCKET *)fd->inode->internal_object;
+  OPEN_INET_SOCKET *inet = s->child;
+  assert(inet);
+  struct sockaddr_in in;
+  in.sin_addr.s_addr = inet->address;
+  in.sin_port = inet->port;
+  send_udp_packet(&in, (const struct sockaddr_in *)dest_addr, message, length);
+  return length; // FIXME: This is probably not true.
+}
diff --git a/scalls/sendto.h b/scalls/sendto.h
new file mode 100644
index 0000000..0f852de
--- /dev/null
+++ b/scalls/sendto.h
@@ -0,0 +1,11 @@
+#include <socket.h>
+#include <stdint.h>
+
+struct t_two_args {
+  uint32_t a;
+  uint32_t b;
+};
+size_t syscall_sendto(int socket, const void *message, size_t length,
+           int flags, struct t_two_args *extra_args /*
+	   const struct sockaddr *dest_addr,
+           socklen_t dest_len*/);
diff --git a/socket.c b/socket.c
index 4ef4b3a..0519c65 100644
--- a/socket.c
+++ b/socket.c
@@ -111,6 +111,7 @@ int bind(int sockfd, const struct sockaddr *addr, socklen_t addrlen) {
 
     us->path = s->path;
     us->s = s;
+    s->child = us;
     devfs_add_file(us->path, NULL, NULL, NULL, 1, 1, FS_TYPE_UNIX_SOCKET);
     return 0;
   }
@@ -127,6 +128,7 @@ int bind(int sockfd, const struct sockaddr *addr, socklen_t addrlen) {
     inet->address = in->sin_addr.s_addr;
     inet->port = in->sin_port;
     inet->s = s;
+    s->child = inet;
     return 0;
   }
   return 0;
diff --git a/socket.h b/socket.h
index 168386e..bb278c1 100644
--- a/socket.h
+++ b/socket.h
@@ -22,6 +22,7 @@ typedef struct {
   int domain;
   int type;
   int protocol;
+  void *child;
 
   // UNIX socket
   char *path;
@@ -53,6 +54,7 @@ struct sockaddr_in {
   sa_family_t sin_family;
   union {
     uint32_t s_addr;
+    uint8_t a[4];
   } sin_addr;
   uint16_t sin_port;
 };
diff --git a/userland/libc/Makefile b/userland/libc/Makefile
index 02f5584..bcb82f8 100644
--- a/userland/libc/Makefile
+++ b/userland/libc/Makefile
@@ -2,7 +2,7 @@ CC="i686-sb-gcc"
 AR="i686-sb-ar"
 AS="i686-sb-as"
 CFLAGS = -ggdb -ffreestanding -O2 -Wall -pedantic -Wimplicit-fallthrough -I./include/ -static
-OBJ=crt0.o libc.o malloc/malloc.o pty.o sys/mman/mmap.o memset.o assert.o stdio/snprintf.o stdio/vfprintf.o string/memcpy.o string/memcmp.o string/strcmp.o ubsan.o string/strcpy.o isspace.o stdio/puts.o stdio/putchar.o dirent/opendir.o dirent/readdir.o dirent/closedir.o unistd/getopt.o dirent/scandir.o dirent/alphasort.o stdio/printf.o stdio/vdprintf.o stdio/vprintf.o stdio/dprintf.o stdio/vprintf.o string/strlen.o string/strnlen.o stdio/stdin.o stdio/getchar.o stdio/fgetc.o arpa/inet/htons.o arpa/inet/htonl.o stdio/fread.o stdio/fwrite.o stdio/fopen.o stdio/fclose.o stdio/fseek.o ctype/isascii.o stdio/fprintf.o stdlib/atoi.o stdlib/strtol.o ctype/toupper.o ctype/tolower.o string/strcat.o string/strchr.o string/sscanf.o sys/stat/stat.o stdlib/getenv.o string/strrchr.o stdio/ftell.o stdio/tmpfile.o stdio/fgets.o stdio/feof.o stdio/fscanf.o stdio/ungetc.o string/strncmp.o stdio/fputc.o string/strncpy.o stdio/remove.o stdio/ferror.o stdio/fputs.o stdlib/rand.o stdlib/srand.o unistd/getpid.o stdlib/strtoul.o stdio/fflush.o stdlib/abort.o string/strcspn.o time/localtime.o time/time.o time/clock_gettime.o time/gmtime.o time/strftime.o string/strpbrk.o ctype/isdigit.o ctype/isalpha.o ctype/isxdigit.o ctype/ispunct.o stdio/setvbuf.o stdio/fileno.o stdio/putc.o stdio/sprintf.o stdlib/abs.o string/strspn.o stdlib/qsort.o string/memmove.o setjmp/longjmp.o setjmp/setjmp.o libgen/basename.o string/strdup.o string/strndup.o string/strlcpy.o stdlib/atexit.o stdio/open_memstream.o libgen/dirname.o unistd/unlink.o string/strstr.o string/strcasecmp.o string/strncasecmp.o stdlib/mkstemp.o string/strtok.o unistd/execvp.o unistd/_exit.o ctype/isalnum.o time/ctime_r.o stdlib/strtold.o sys/time/gettimeofday.o stdio/fgetpos.o stdio/fsetpos.o ctype/isprint.o stdlib/system.o stdio/tmpnam.o unistd/msleep.o stdlib/atof.o stdlib/strtod.o stdio/rename.o sys/stat/mkdir.o unistd/uptime.o unistd/ftruncate.o sys/socket/recvfrom.o
+OBJ=crt0.o libc.o malloc/malloc.o pty.o sys/mman/mmap.o memset.o assert.o stdio/snprintf.o stdio/vfprintf.o string/memcpy.o string/memcmp.o string/strcmp.o ubsan.o string/strcpy.o isspace.o stdio/puts.o stdio/putchar.o dirent/opendir.o dirent/readdir.o dirent/closedir.o unistd/getopt.o dirent/scandir.o dirent/alphasort.o stdio/printf.o stdio/vdprintf.o stdio/vprintf.o stdio/dprintf.o stdio/vprintf.o string/strlen.o string/strnlen.o stdio/stdin.o stdio/getchar.o stdio/fgetc.o arpa/inet/htons.o arpa/inet/htonl.o stdio/fread.o stdio/fwrite.o stdio/fopen.o stdio/fclose.o stdio/fseek.o ctype/isascii.o stdio/fprintf.o stdlib/atoi.o stdlib/strtol.o ctype/toupper.o ctype/tolower.o string/strcat.o string/strchr.o string/sscanf.o sys/stat/stat.o stdlib/getenv.o string/strrchr.o stdio/ftell.o stdio/tmpfile.o stdio/fgets.o stdio/feof.o stdio/fscanf.o stdio/ungetc.o string/strncmp.o stdio/fputc.o string/strncpy.o stdio/remove.o stdio/ferror.o stdio/fputs.o stdlib/rand.o stdlib/srand.o unistd/getpid.o stdlib/strtoul.o stdio/fflush.o stdlib/abort.o string/strcspn.o time/localtime.o time/time.o time/clock_gettime.o time/gmtime.o time/strftime.o string/strpbrk.o ctype/isdigit.o ctype/isalpha.o ctype/isxdigit.o ctype/ispunct.o stdio/setvbuf.o stdio/fileno.o stdio/putc.o stdio/sprintf.o stdlib/abs.o string/strspn.o stdlib/qsort.o string/memmove.o setjmp/longjmp.o setjmp/setjmp.o libgen/basename.o string/strdup.o string/strndup.o string/strlcpy.o stdlib/atexit.o stdio/open_memstream.o libgen/dirname.o unistd/unlink.o string/strstr.o string/strcasecmp.o string/strncasecmp.o stdlib/mkstemp.o string/strtok.o unistd/execvp.o unistd/_exit.o ctype/isalnum.o time/ctime_r.o stdlib/strtold.o sys/time/gettimeofday.o stdio/fgetpos.o stdio/fsetpos.o ctype/isprint.o stdlib/system.o stdio/tmpnam.o unistd/msleep.o stdlib/atof.o stdlib/strtod.o stdio/rename.o sys/stat/mkdir.o unistd/uptime.o unistd/ftruncate.o sys/socket/recvfrom.o sys/socket/sendto.o
 all: libc.a
 
 %.o: %.c
diff --git a/userland/libc/include/sys/socket.h b/userland/libc/include/sys/socket.h
index 18402d0..c4f10e2 100644
--- a/userland/libc/include/sys/socket.h
+++ b/userland/libc/include/sys/socket.h
@@ -5,3 +5,5 @@
 
 size_t recvfrom(int socket, void *buffer, size_t length, int flags,
                 struct sockaddr *address, socklen_t *address_len);
+size_t sendto(int socket, const void *message, size_t length, int flags,
+               const struct sockaddr *dest_addr, socklen_t dest_len);
diff --git a/userland/libc/include/syscall.h b/userland/libc/include/syscall.h
index 7d84b8f..3af425d 100644
--- a/userland/libc/include/syscall.h
+++ b/userland/libc/include/syscall.h
@@ -33,6 +33,7 @@
 #define SYS_UPTIME 25
 #define SYS_MKDIR 26
 #define SYS_RECVFROM 27
+#define SYS_SENDTO 28
 
 int syscall(uint32_t eax, uint32_t ebx, uint32_t ecx, uint32_t edx,
             uint32_t esi, uint32_t edi);
diff --git a/userland/libc/sys/socket/recvfrom.c b/userland/libc/sys/socket/recvfrom.c
new file mode 100644
index 0000000..5bbfeea
--- /dev/null
+++ b/userland/libc/sys/socket/recvfrom.c
@@ -0,0 +1,17 @@
+#include <assert.h>
+#include <sys/socket.h>
+#include <syscall.h>
+
+struct two_args {
+  uint32_t a;
+  uint32_t b;
+};
+
+size_t recvfrom(int socket, void *buffer, size_t length, int flags,
+                struct sockaddr *address, socklen_t *address_len) {
+  struct two_args extra_args;
+  extra_args.a = address;
+  extra_args.b = address_len;
+
+  return syscall(SYS_RECVFROM, socket, buffer, length, flags, &extra_args);
+}
diff --git a/userland/libc/sys/socket/sendto.c b/userland/libc/sys/socket/sendto.c
new file mode 100644
index 0000000..73437ab
--- /dev/null
+++ b/userland/libc/sys/socket/sendto.c
@@ -0,0 +1,16 @@
+#include <sys/socket.h>
+#include <syscall.h>
+
+struct two_args {
+  uint32_t a;
+  uint32_t b;
+};
+
+size_t sendto(int socket, const void *message, size_t length, int flags,
+               const struct sockaddr *dest_addr, socklen_t dest_len) {
+  struct two_args extra = {
+      .a = dest_addr,
+      .b = dest_len,
+  };
+  return syscall(SYS_SENDTO, socket, message, length, flags, &extra);
+}