Theory JVMExceptions

theory JVMExceptions
imports JVMInstructions
(*  Title:      HOL/MicroJava/JVM/JVMExceptions.thy
Author: Gerwin Klein, Martin Strecker
Copyright 2001 Technische Universitaet Muenchen

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

theory JVMExceptions imports JVMInstructions begin

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

primrec match_exception_table :: "jvm_prog => cname => p_count => exception_table
=> p_count option"

"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)"

ex_table_of :: "jvm_method => exception_table"
where "ex_table_of m == snd (snd (snd m))"

primrec find_handler :: "jvm_prog => val option => aheap => frame list
=> jvm_state"

"find_handler G xcpt hp [] = (xcpt, hp, [])"
| "find_handler G xcpt hp (fr#frs) =
(case xcpt of
None => (None, hp, fr#frs)
| Some xc =>
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 => find_handler G (Some xc) hp frs
| Some handler_pc => (None, hp, ([xc], loc, C, sig, handler_pc)#frs)))"

text {*
System exceptions are allocated in all heaps:

text {*
Only program counters that are mentioned in the exception table
can be returned by @{term match_exception_table}:

lemma match_exception_table_in_et:
"match_exception_table G C pc et = Some pc' ==> ∃e ∈ set et. pc' = fst (snd (snd e))"
by (induct et) (auto split: split_if_asm)