src/arch/x86/syscall.c

@@ -4,21 +4,57 @@
  * @license GPL-3.0-only
  */
 
+#include "sched/scheduler.h"
 #include <arch/x86.h>
 #include <kernel.h>
+#include <stddef.h>
+#include <io/term/term.h>
 
+void sys_write(unsigned int fd, const char* buf, size_t count)
+{
+    switch (fd) {
+        case 1: //stdout
+            for (size_t i=0; i<count; i++) {
+                internal_putc(buf[i], NULL);
+            }
+            break;
+
+        case 2: //stderr
+            break;
+    }
+}
+
+/*
+ * syscall_handler - System call dispatcher
+ * @regs: CPU state
+ *
+ * This function is called from the interrupt dispatcher,
+ * when an interrupt 0x80 is emitted from userland.
+ *
+ * It switches control to the syscall number provided
+ * in %rax. 
+ *
+ * We try to follow the System V convention here:
+ * - syscall number in %rax
+ * - args in %rdi, %rsi, %rdx, %r10, %r8, %r9
+ * - return value (if any) in %rax
+ *
+ * Return:
+ * <regs> - CPU state after system call
+ */
 struct cpu_status* syscall_handler(struct cpu_status* regs)
 {
-    DEBUG("Syscall %lx with argument %lx", regs->rdi, regs->rsi);
+    DEBUG("Syscall %lx with (arg0=%lx arg1=%lx)", regs->rax, regs->rdi, regs->rsi);
 
-    switch (regs->rdi)
+    switch (regs->rax)
     {
-        case 0:
+        case 0: //sys_read
             break;
-        case 1:
+        case 1: //sys_write
+            sys_write(regs->rdi, (char*)regs->rsi, regs->rdx);
             break;
         default:
-            regs->rsi = 0xdeadbeef;
+            regs->rax = 0xbad515ca11;
             break;
     }
 

user/hello.S

@@ -1,4 +1,16 @@
 bits 64
 
+section .data
+    hi db "hi from userland :) we did it man", 0
+
+section .text
+
 hello:
-    mov rax, 0xcafebabe
+    mov rax, 0x1        ;sys_write
+    mov rdi, 0x1        ;stdout
+    lea rsi, [rel hi]   ;char* buf
+    mov rdx, 33         ;count
+    int 0x80
+
+.loop:
+    jmp .loop