src/HOL/MicroJava/JVM/JVMExceptions.thy

canonical start state

(*  Title:      HOL/MicroJava/JVM/JVMExceptions.thy
    ID:         $Id$
    Author:     Gerwin Klein, Martin Strecker
    Copyright   2001 Technische Universitaet Muenchen
*)

header {* \isaheader{Exception handling in the JVM} *}

theory JVMExceptions = JVMInstructions:

constdefs
  match_exception_entry :: "jvm_prog \<Rightarrow> cname \<Rightarrow> p_count \<Rightarrow> exception_entry \<Rightarrow> bool"
  "match_exception_entry G cn pc ee == 
                 let (start_pc, end_pc, handler_pc, catch_type) = ee in
                 start_pc <= pc \<and> pc < end_pc \<and> G\<turnstile> cn \<preceq>C catch_type"


consts
  match_exception_table :: "jvm_prog \<Rightarrow> cname \<Rightarrow> p_count \<Rightarrow> exception_table
                          \<Rightarrow> p_count option"
primrec
  "match_exception_table G cn pc []     = None"
  "match_exception_table G cn pc (e#es) = (if match_exception_entry G cn pc e
                                           then Some (fst (snd (snd e))) 
                                           else match_exception_table G cn pc es)"


consts
  cname_of :: "aheap \<Rightarrow> val \<Rightarrow> cname"
  ex_table_of :: "jvm_method \<Rightarrow> exception_table"

translations
  "cname_of hp v" == "fst (the (hp (the_Addr v)))"
  "ex_table_of m" == "snd (snd (snd m))"


consts
  find_handler :: "jvm_prog \<Rightarrow> val option \<Rightarrow> aheap \<Rightarrow> frame list \<Rightarrow> jvm_state"
primrec
  "find_handler G xcpt hp [] = (xcpt, hp, [])"
  "find_handler G xcpt hp (fr#frs) = 
      (case xcpt of
         None \<Rightarrow> (None, hp, fr#frs)
       | Some xc \<Rightarrow> 
       let (stk,loc,C,sig,pc) = fr in
       (case match_exception_table G (cname_of hp xc) pc 
              (ex_table_of (snd(snd(the(method (G,C) sig))))) of
          None \<Rightarrow> find_handler G (Some xc) hp frs
        | Some handler_pc \<Rightarrow> (None, hp, ([xc], loc, C, sig, handler_pc)#frs)))"


text {*
  System exceptions are allocated in all heaps:
*}
constdefs
  preallocated :: "aheap \<Rightarrow> bool"
  "preallocated hp \<equiv> \<forall>x. \<exists>fs. hp (XcptRef x) = Some (Xcpt x, fs)"

lemma preallocatedD:
  "preallocated hp \<Longrightarrow> \<exists>fs. hp (XcptRef x) = Some (Xcpt x, fs)"
  by (unfold preallocated_def) fast

lemma preallocatedE [elim?]:
  "preallocated hp \<Longrightarrow> (\<And>fs. hp (XcptRef x) = Some (Xcpt x, fs) \<Longrightarrow> P hp) \<Longrightarrow> P hp"
  by (fast dest: preallocatedD)

lemma cname_of_xcp:
  "raise_system_xcpt b x = Some xcp \<Longrightarrow> preallocated hp 
  \<Longrightarrow> cname_of (hp::aheap) xcp = Xcpt x"
proof -
  assume "raise_system_xcpt b x = Some xcp"
  hence "xcp = Addr (XcptRef x)"
    by (simp add: raise_system_xcpt_def split: split_if_asm)
  moreover
  assume "preallocated hp" 
  then obtain fs where "hp (XcptRef x) = Some (Xcpt x, fs)" ..
  ultimately
  show ?thesis by simp
qed

lemma preallocated_start:
  "preallocated (start_heap G)"
  apply (unfold preallocated_def)
  apply (unfold start_heap_def)
  apply (rule allI)
  apply (case_tac x)
  apply (auto simp add: blank_def)
  done

end