Theory JVMDefensive

theory JVMDefensive
imports JVMExec
(*  Title:      HOL/MicroJava/JVM/JVMDefensive.thy
    Author:     Gerwin Klein
*)

header {* \isaheader{A Defensive JVM} *}

theory JVMDefensive
imports JVMExec
begin

text {*
  Extend the state space by one element indicating a type error (or
  other abnormal termination) *}
datatype 'a type_error = TypeError | Normal 'a


abbreviation
  fifth :: "'a × 'b × 'c × 'd × 'e × 'f => 'e"
  where "fifth x == fst(snd(snd(snd(snd x))))"

fun isAddr :: "val => bool" where
  "isAddr (Addr loc) = True"
| "isAddr v          = False"

fun isIntg :: "val => bool" where
  "isIntg (Intg i) = True"
| "isIntg v        = False"

definition isRef :: "val => bool" where
  "isRef v ≡ v = Null ∨ isAddr v"

primrec check_instr :: "[instr, jvm_prog, aheap, opstack, locvars, 
                  cname, sig, p_count, nat, frame list] => bool" where
  "check_instr (Load idx) G hp stk vars C sig pc mxs frs = 
  (idx < length vars ∧ size stk < mxs)"

| "check_instr (Store idx) G hp stk vars Cl sig pc mxs frs = 
  (0 < length stk ∧ idx < length vars)"

| "check_instr (LitPush v) G hp stk vars Cl sig pc mxs frs = 
  (¬isAddr v ∧ size stk < mxs)"

| "check_instr (New C) G hp stk vars Cl sig pc mxs frs = 
  (is_class G C ∧ size stk < mxs)"

| "check_instr (Getfield F C) G hp stk vars Cl sig pc mxs frs = 
  (0 < length stk ∧ is_class G C ∧ field (G,C) F ≠ None ∧ 
  (let (C', T) = the (field (G,C) F); ref = hd stk in 
    C' = C ∧ isRef ref ∧ (ref ≠ Null --> 
      hp (the_Addr ref) ≠ None ∧ 
      (let (D,vs) = the (hp (the_Addr ref)) in 
        G \<turnstile> D \<preceq>C C ∧ vs (F,C) ≠ None ∧ G,hp \<turnstile> the (vs (F,C)) ::\<preceq> T))))" 

| "check_instr (Putfield F C) G hp stk vars Cl sig pc mxs frs = 
  (1 < length stk ∧ is_class G C ∧ field (G,C) F ≠ None ∧ 
  (let (C', T) = the (field (G,C) F); v = hd stk; ref = hd (tl stk) in 
    C' = C ∧ isRef ref ∧ (ref ≠ Null --> 
      hp (the_Addr ref) ≠ None ∧ 
      (let (D,vs) = the (hp (the_Addr ref)) in 
        G \<turnstile> D \<preceq>C C ∧ G,hp \<turnstile> v ::\<preceq> T))))" 

| "check_instr (Checkcast C) G hp stk vars Cl sig pc mxs frs =
  (0 < length stk ∧ is_class G C ∧ isRef (hd stk))"

| "check_instr (Invoke C mn ps) G hp stk vars Cl sig pc mxs frs =
  (length ps < length stk ∧ 
  (let n = length ps; v = stk!n in
  isRef v ∧ (v ≠ Null --> 
    hp (the_Addr v) ≠ None ∧
    method (G,cname_of hp v) (mn,ps) ≠ None ∧
    list_all2 (λv T. G,hp \<turnstile> v ::\<preceq> T) (rev (take n stk)) ps)))"
  
| "check_instr Return G hp stk0 vars Cl sig0 pc mxs frs =
  (0 < length stk0 ∧ (0 < length frs --> 
    method (G,Cl) sig0 ≠ None ∧    
    (let v = hd stk0;  (C, rT, body) = the (method (G,Cl) sig0) in
    Cl = C ∧ G,hp \<turnstile> v ::\<preceq> rT)))"
 
| "check_instr Pop G hp stk vars Cl sig pc mxs frs = 
  (0 < length stk)"

| "check_instr Dup G hp stk vars Cl sig pc mxs frs = 
  (0 < length stk ∧ size stk < mxs)"

| "check_instr Dup_x1 G hp stk vars Cl sig pc mxs frs = 
  (1 < length stk ∧ size stk < mxs)"

| "check_instr Dup_x2 G hp stk vars Cl sig pc mxs frs = 
  (2 < length stk ∧ size stk < mxs)"

| "check_instr Swap G hp stk vars Cl sig pc mxs frs =
  (1 < length stk)"

| "check_instr IAdd G hp stk vars Cl sig pc mxs frs =
  (1 < length stk ∧ isIntg (hd stk) ∧ isIntg (hd (tl stk)))"

| "check_instr (Ifcmpeq b) G hp stk vars Cl sig pc mxs frs =
  (1 < length stk ∧ 0 ≤ int pc+b)"

| "check_instr (Goto b) G hp stk vars Cl sig pc mxs frs =
  (0 ≤ int pc+b)"

| "check_instr Throw G hp stk vars Cl sig pc mxs frs =
  (0 < length stk ∧ isRef (hd stk))"

definition check :: "jvm_prog => jvm_state => bool" where
  "check G s ≡ let (xcpt, hp, frs) = s in
               (case frs of [] => True | (stk,loc,C,sig,pc)#frs' => 
                (let  (C',rt,mxs,mxl,ins,et) = the (method (G,C) sig); i = ins!pc in
                 pc < size ins ∧ 
                 check_instr i G hp stk loc C sig pc mxs frs'))"


definition exec_d :: "jvm_prog => jvm_state type_error => jvm_state option type_error" where
  "exec_d G s ≡ case s of 
      TypeError => TypeError 
    | Normal s' => if check G s' then Normal (exec (G, s')) else TypeError"


definition
  exec_all_d :: "jvm_prog => jvm_state type_error => jvm_state type_error => bool" 
                   ("_ \<turnstile> _ \<midarrow>jvmd-> _" [61,61,61]60) where
  "G \<turnstile> s \<midarrow>jvmd-> t <->
         (s,t) ∈ ({(s,t). exec_d G s = TypeError ∧ t = TypeError} ∪
                  {(s,t). ∃t'. exec_d G s = Normal (Some t') ∧ t = Normal t'})*"


declare split_paired_All [simp del]
declare split_paired_Ex [simp del]

lemma [dest!]:
  "(if P then A else B) ≠ B ==> P"
  by (cases P, auto)

lemma exec_d_no_errorI [intro]:
  "check G s ==> exec_d G (Normal s) ≠ TypeError"
  by (unfold exec_d_def) simp

theorem no_type_error_commutes:
  "exec_d G (Normal s) ≠ TypeError ==> 
  exec_d G (Normal s) = Normal (exec (G, s))"
  by (unfold exec_d_def, auto)


lemma defensive_imp_aggressive:
  "G \<turnstile> (Normal s) \<midarrow>jvmd-> (Normal t) ==> G \<turnstile> s \<midarrow>jvm-> t"
proof -
  have "!!x y. G \<turnstile> x \<midarrow>jvmd-> y ==> ∀s t. x = Normal s --> y = Normal t -->  G \<turnstile> s \<midarrow>jvm-> t"
    apply (unfold exec_all_d_def)
    apply (erule rtrancl_induct)
     apply (simp add: exec_all_def)
    apply (fold exec_all_d_def)
    apply simp
    apply (intro allI impI)
    apply (erule disjE, simp)
    apply (elim exE conjE)
    apply (erule allE, erule impE, assumption)
    apply (simp add: exec_all_def exec_d_def split: type_error.splits split_if_asm)
    apply (rule rtrancl_trans, assumption)
    apply blast
    done
  moreover
  assume "G \<turnstile> (Normal s) \<midarrow>jvmd-> (Normal t)" 
  ultimately
  show "G \<turnstile> s \<midarrow>jvm-> t" by blast
qed

end