jit: implement call instruction

The generated code is suboptimal right now, since it does an indirect call and
has to save registers 6 and 7 on the stack. These issues will be fixed.

test_framework/test_jit.py

@@ -35,8 +35,13 @@ def check_datafile(filename):
         memfile.write(data['mem'])
         memfile.flush()
 
+    num_register_offsets = 20
+    if 'no register offset' in data:
+        # The JIT relies on a fixed register mapping for the call instruction
+        num_register_offsets = 1
+
     try:
-        for register_offset in xrange(0, 20):
+        for register_offset in xrange(0, num_register_offsets):
             cmd = [VM]
             if memfile:
                 cmd.extend(['-m', memfile.name])

tests/call-memfrob.data

@@ -10,5 +10,5 @@ exit
 01 02 03 04 05 06 07 08
 -- result
 0x102292e2f2c0708
--- no jit
-CALL not yet implemented
+-- no register offset
+call instruction

tests/call-save.data

@@ -0,0 +1,16 @@
+-- asm
+mov r6, 0x0001
+mov r7, 0x0020
+mov r8, 0x0300
+mov r9, 0x4000
+call 2
+mov r0, 0
+or r0, r6
+or r0, r7
+or r0, r8
+or r0, r9
+exit
+-- result
+0x4321
+-- no register offset
+call instruction

tests/call.data

@@ -8,5 +8,5 @@ call 0
 exit
 -- result
 0x0102030405
--- no jit
-CALL not yet implemented
+-- no register offset
+call instruction

vm/test.c

@@ -182,9 +182,27 @@ gather_bytes(uint8_t a, uint8_t b, uint8_t c, uint8_t d, uint8_t e)
         e;
 }
 
+static void
+trash_registers(void)
+{
+    /* Overwrite all caller-save registers */
+    asm(
+        "mov $0xf0, %rax;"
+        "mov $0xf1, %rcx;"
+        "mov $0xf2, %rdx;"
+        "mov $0xf3, %rsi;"
+        "mov $0xf4, %rdi;"
+        "mov $0xf5, %r8;"
+        "mov $0xf6, %r9;"
+        "mov $0xf7, %r10;"
+        "mov $0xf8, %r11;"
+    );
+}
+
 static void
 register_functions(struct ubpf_vm *vm)
 {
     ubpf_register(vm, 0, "gather_bytes", gather_bytes);
     ubpf_register(vm, 1, "memfrob", memfrob);
+    ubpf_register(vm, 2, "trash_registers", trash_registers);
 }

vm/ubpf_jit.dasm

@@ -422,6 +422,20 @@ ubpf_compile(struct ubpf_vm *vm, char **errmsg)
             | cmp Rq(dst), Rq(src)
             | jge =>jmp_target
             break;
+        case EBPF_OP_CALL:
+            /* TODO use callee save registers for these */
+            | push r10
+            | push r11
+            /* TODO fix register assignment */
+            | mov rcx, r8
+            | mov r8, r9
+            /* TODO direct call */
+            | mov rax, vm->ext_funcs[inst.imm]
+            | call rax
+            /* TODO use callee save registers for these */
+            | pop r11
+            | pop r10
+            break;
         case EBPF_OP_EXIT:
             if (i != vm->num_insts - 1) {
                 | jmp ->exit