kernel: Various changes

+ elf: Prevent dynamically linked programs from running on Soaplin.
+ sched: Support creating a process from a program_t structure.
+ syscall: Fix a bug where using syscall number 1024 would crash the OS.
+ syscall: Added a write syscall. It can only be used for writing to the standard output (FD: 1)

kernel/src/exec/elf.c

@@ -47,6 +47,12 @@ program_t *elf_load(char *data, int user) {
 
   for (uint16_t i = 0; i < ehdr->e_phnum; i++) {
     log("elf - ELF segment type: %d\n", phdr[i].p_type);
+
+    if (phdr[i].p_type == PT_INTERP) {
+      log("elf - A PT_INTERP program header was found. This was meant to be a dynamically-linked program, which Soaplin doesn't supports.\n");
+      return NULL;
+    }
+
     if (phdr[i].p_type != PT_LOAD)
       continue;
 
@@ -58,7 +64,9 @@ program_t *elf_load(char *data, int user) {
     uint64_t flags = VMM_PRESENT;
     if (phdr[i].p_flags & PF_W)
       flags |= VMM_WRITABLE;
-    if (!(phdr[i].p_flags & PF_X))
+    if (phdr[i].p_flags & PF_X)
+      flags &= ~VMM_NX;
+    else
       flags |= VMM_NX;
 
     if (user)

kernel/src/main.c

@@ -131,7 +131,7 @@ void __kmain(void) {
 
 
   sched_process *proc =
-      sched_create("Test", p->entry, p->pm, SCHED_USER_PROCESS);
+      sched_from_program(p);
 
   log("kernel - Soaplin initialized sucessfully.\n");
 

kernel/src/sched/sched.c

@@ -119,6 +119,10 @@ sched_process *sched_create(char *name, uint64_t entry_point, pagemap_t *pm,
   return proc;
 }
 
+sched_process *sched_from_program(program_t *prog) {
+  // D̶̡͖̼̪̩̽̃̿͐͐̀̑͐̑ǫ̴͚̘̩̗̠̣̗͇̳̀̅̈͌͆͆ ̸̢̢̯͎̳̟̑͋́N̷̹͛̋͗ö̴͇̼̖̝̼́̀̾̿̾̓̔̌t̵̯̘͇̙̬̤̫͚͓̠͔̭̚ͅ ̵͔̲͈̭͛̆̈Ú̷̱̈́͑́̇̀̈́̔͝͠s̴̢͇̳̯̬͔̦̗̯̜̀̓̎̆̅̈́̈́̑̾͆͌̆͝ê̴̛͎̪̩̙͕̖͖͍͓͐̊̈͋̆̂̌̍̂͘͘̚ ̵̢̢͖̦̬͔̻͇̠̺̂͒͌͌̈́̇̏͑͋̓̔̅̓͂͝S̴̡͇͎̠̯͙̖̲̮͓͋͊̐̋̑́͂͆̿C̵̤̲͉̫̜͓͇̙͇̪̥̈̂́̈́͋̃̿̕H̶̡͓̠̝͉͋͋̎̃E̶͉̬̞̖̮͚̙͗̔̋͆Ḑ̴̛͎̙̥̱̱͎͊͊͋̈́̆̎̓͑̚̚_̷͚̯̻̖͈̳̺̖̈͗́̽͠Ḱ̴̮͓̲̠̫͈̆̿͂͂̀̂͆̀́̔͝ͅḘ̷̡͔̘̒̒̐͆̍̀R̵̭̰̐́̾̈́̈́̋͗̎̉͐͝N̴̰͆̂͛̂̈́̄̊͌̓͆̕͘͠͠Ě̴̥͙̼̳̩̠͓͕̫͔̘̠̻̀͌̓͑́̓̂̋̌͘͜L̴̙͓̣̭̙͙͈̺̩̄̈͆͆͒͗͛̈́̎̉̈́͘͘͜͠_̵̭̱͇͍̩̬͌̿͂͊̐͘̕ͅP̵̡̪̹̀͂̀̋̇̓͘͜Ŕ̸̭͍̮̼̙͓͕̳̫̇̏͌͌̋͜͝Ǫ̵̛͎̭̱͈̫̮̘͉͔̪̟̺̥̉̈̈́̊́̕̕͠ͅC̵̡̡͕̱̠̝̭͓̗̜͇̼̳̲͓̑̽̔̑͠Ę̷̛̦̑̈̒̃̊̈́̓̚̚͜͠͝Ş̴̥͇̬̱̠̟͙̳̖̿͗̀͌͊̽̐͒̃͜S̴͉͖͉͎͎̱̝͔̙̜̭̍͑͊̒͆̃͗̂͌̽͑̓ͅ ̶̼̥̜͙͈̦̲̰̞̈́̑͆̂͝H̸̩̭̹̘̩̊͗̔̉̓̈́ȩ̷̩͍͚̮̰̭̘͍͇͈̺͇̻̓̀̅̊́̓̈́͗̇̔̓͛͜͝ṙ̶̡̩̜̜̭̝̪͔͙̟̣͉̆͗̉͜͠͝ͅę̷̡̦̘̰͖̲͉̤̼͈̺̺̦̯̿͌́͐̃̃͂̾́̊́.̶̡̧͈͍͈̟̠͙̘̤̝̪̽̊̈͐̕͜
+  return sched_create("unknown program", prog->entry, prog->pm, SCHED_USER_PROCESS);
+}
 void sched_exit(int exit_code) {
   log("sched - Process %d exited with code %d!", curr_proc->pid, exit_code);
   curr_proc->type = SCHED_DIED;

kernel/src/sched/sched.h

@@ -1,6 +1,7 @@
 #pragma once
 
 #include "arch/x86_64/idt.h"
+#include "exec/exec.h"
 #include "mm/vmm.h"
 
 #define SCHED_KERNEL_PROCESS 0 // A process that runs in kernel mode.
@@ -38,5 +39,8 @@ extern sched_process *proc_list;
 void sched_init();
 sched_process *sched_create(char *name, uint64_t entry_point, pagemap_t *pm,
                             uint32_t flags);
+
+sched_process *sched_from_program(program_t *prog);
+
 void sched_exit(int exit_code);
 void schedule(registers_t *regs);

kernel/src/sys/syscall.c

@@ -14,7 +14,7 @@ extern void __x86_64_syscall_init();
 static uint64_t __syscall_undefined() { return 0; }
 
 void syscall_handle(registers_t *regs) {
-  if (regs->rax > 1024) {
+  if (regs->rax >= 1024) {
     log("syscall - syscall_handle was called with rax better than what Soaplin "
         "supports (1024). did you forget to set rax?\n");
     return;
@@ -50,13 +50,15 @@ void syscall_register(int id, syscall handler) {
   log("syscall - System call %d has been set to %p\n", id, handler);
 }
 
+extern void syscall_write(int fd, const char *buf, size_t count);
 extern void syscall_exit(int exit_code);
 
 void syscall_init() {
   for (int i = 0; i < 1024; i++)
     syscall_table[i] = (syscall)__syscall_undefined;
 
-  syscall_register(0, (syscall)syscall_exit);
+  syscall_register(1, (syscall)syscall_write);
+  syscall_register(60, (syscall)syscall_exit);
 
   __x86_64_syscall_init();
 }

kernel/src/sys/syscalls/syscalls_fs.c

@@ -0,0 +1,11 @@
+#include <stddef.h>
+#include <sys/printf.h>
+
+int syscall_write(int fd, const char *buf, size_t count) {
+  if (fd == 1) {
+    printf("%s", buf); // Prevent the buffer from being formatted.
+    return count;
+  }
+
+  return 0;
+}

testing/test.asm

@@ -1,9 +1,18 @@
 bits 64
+
 section .text
     global _start
 
 _start:
-    mov rax, 1025
+    mov rax, 1      ; write syscall number
+    mov rdi, 1      ; stdout file descriptor
+    mov rsi, msg    ; pointer to message
+    mov rdx, msg_len ; message length
     syscall
+
 .loop:
-    jmp .loop
+    jmp .loop
+
+section .data
+    msg db "Hello, World. Technically, this should work on both Soaplin & Linux.", 10    ; 10 is newline
+    msg_len equ $ - msg