Übung 5

Assets/Betriebssysteme_uebung/u6-a1-anlage/syscall.c

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+/* syscall.c
+ *
+ * Call OS functions without using libc. The example `my_print` could be done in
+ * different flavors:
+ *
+ * **my_print_64:**
+ *   Using the SYSCALL instruction (successor to SYSENTER). Should work for both
+ *   IA-64 and AMD64 CPUs, can be ported to `my_print_trap` (see there).
+ *   Register usage:
+ *
+ *     - RAX: pass syscall number, hold return value from syscall execution
+ *     - RDI: syscall argument 1
+ *     - RSI: syscall argument 2
+ *     - RDX: syscall argument 3
+ *
+ * **my_print_trap:**
+ *   Using the trap interrupt to switch to kernel mode. Slower, but
+ *   architecturally neutral. Register usage:
+ *
+ *     - EAX: pass syscall number, hold return value from syscall execution
+ *     - EBX: syscall argument 1
+ *     - ECX: syscall argument 2
+ *     - EDX: syscall argument 3
+ */
+
+#include <asm/unistd.h> /* compile with -m32 for 32-bit syscall numbers,
+                           without for 64-bit syscall numbers. */
+/* simple inline assembler (asm) requires global symbols */
+#define __NR_exit 60
+// text buffer pointer
+char *my_print_text;
+// text buffer length, print return value
+int my_print_len, my_print_ret;
+// write() syscall number
+int call_write;
+int exitnum; 
+
+int my_print_64(char *text) {
+    my_print_text = text;
+
+    /* strlen(my_print_text) manually */
+    for (my_print_len = 0; my_print_text[my_print_len]; ++my_print_len);
+
+    /* system call signature:
+     * ssize_t write(int fd, const void *buf, size_t count);
+     *
+     * write() system call number is defined by __NR_write
+     */
+    call_write = __NR_write;
+    /* stdout is file descriptor no. 1 */
+    asm("mov call_write, %rax");    /* arg 0 (rax): syscall number  */
+    asm("mov $1, %rdi");            /* arg 1 (rdi): file descriptor */
+    asm("mov my_print_text, %rsi"); /* arg 2 (rsi): buffer          */
+    asm("mov my_print_len, %rdx");  /* arg 3 (rdx): length          */
+    asm("syscall");                 /* SYSCALL instruction          */
+    asm("mov %rax, my_print_ret");  /* save return code (rax)       */
+
+    return my_print_ret;
+}
+
+int my_print_trap(char *text) {
+    /* system call signature: see my_print_64 */
+
+    /* TODO */
+
+    return 7;
+}
+
+/* simple inline assembler (asm) requires global symbols */
+
+// exit return value
+int my_exit_status;
+
+void my_exit_64(int status) {
+    my_exit_status = status;
+
+    /* system call signature:
+     * void exit(int status);
+     *
+     * exit() system call number is defined by __NR_exit
+     */
+
+    /* TODO */
+    // Syscall
+   //exitnum = __NR_exit;
+   //asm("mov $60, %rax"); // verwende den exitnum / 60 Syscall
+   //asm("mov my_exit_status, %rdi"); //status = myexitstatus oder 0 
+   //asm("syscall");
+   //TRAP 
+   asm("mov $1, %eax");
+   asm("mov my_exit_status, %ebx");
+   asm("int $0x80"); 
+   
+
+  
+}
+
+int main(void) {
+    my_print_64("Hello World!\n");
+
+    my_exit_64(42);
+
+    /* never come here, if my_exit_64 works */
+    return 6;
+}