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dev:crosscompiler:backend_arm:exceptions

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dev:crosscompiler:backend_arm:exceptions [2019/08/15 18:42]
ursgraf [Java Exceptions]
dev:crosscompiler:backend_arm:exceptions [2019/11/17 18:24] (current)
ursgraf [Floats in Exceptions]
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 ===== ARM Exceptions ===== ===== ARM Exceptions =====
 Each ARM exception is caused by a synchronous or asynchronous event and generally causes the processor to switch its state and jump to its proper exception vector. ​ Each ARM exception is caused by a synchronous or asynchronous event and generally causes the processor to switch its state and jump to its proper exception vector. ​
-[{{ .:ppcexception.png?​550&​direct |//PPC Exceptions and Interrupts//​ }}]+[{{ .:armexception.png?​550&​direct |//ARM Exceptions and Interrupts//​ }}]
 Exception classes and their corresponding exception methods have to be specified in the configuration. Instances of these classes are never created and therefore the object constructors are defined as //​synthetic//​ and will not be translated into code.\\ Exception classes and their corresponding exception methods have to be specified in the configuration. Instances of these classes are never created and therefore the object constructors are defined as //​synthetic//​ and will not be translated into code.\\
 The code generator has to create a special exception stack frame.\\ The code generator has to create a special exception stack frame.\\
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 ===== Floats in Exceptions ===== ===== Floats in Exceptions =====
 +In order to save processing time, floating point registers are not saved when entering exception handling. If an exception method calls a another method which uses EXTRs, however, all volatile EXTR's will be saved by a call to //​US.ENABLE_FLOATS()//​. Nonvolatile EXTR'​s,​ which are used in a method, will be saved on the stack by the prolog of a method in any case. //​US.ENABLE_FLOATS()//​ has to be called in a exception method or in a method which is called by an exception method.\\
 +**Important:​** A decrementer exception calls an action method. The decrementer class could be extended and its action method could be overridden. If this method of the subclass uses floats, you have to insert //​US.ENABLE_FLOATS()//​ as well. 
 +**Important:​** If an exception method or a method called by an exception method uses a method from //​java/​lang/​Math//,​ you have to make sure that //​US.FLOAT_ENABLE()//​ is called.
  
  
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 ==== Supervisor Call Exception ==== ==== Supervisor Call Exception ====
 Each Java exception causes a ARM supervisor call exception. The supervisor call handler receives the thrown exception as a parameter in the first parameter register R0. The code generator has to make sure that this parameter is copied into R0 during the prolog of the program exception handler. The handler does the following: Each Java exception causes a ARM supervisor call exception. The supervisor call handler receives the thrown exception as a parameter in the first parameter register R0. The code generator has to make sure that this parameter is copied into R0 during the prolog of the program exception handler. The handler does the following:
 +  * Get address of causing instruction into variable //addr// from LR. Must happen first, as the next step uses LR as scratch register.
   * increment counter   * increment counter
-  * Get address of causing instruction into variable //addr// from LR. 
   * Read instruction at this address minus 4, because LR points to next instruction   * Read instruction at this address minus 4, because LR points to next instruction
   * Determine from immediate value of instruction which kind of exception was thrown   * Determine from immediate value of instruction which kind of exception was thrown
   * If unchecked instruction:​ create exception such as //​ClassCastException//,​ //​ArrayIndexOutOfBoundsException//,​ etc.   * If unchecked instruction:​ create exception such as //​ClassCastException//,​ //​ArrayIndexOutOfBoundsException//,​ etc.
-  * copy parameter //​exception//​ into register ​R2 +  * copy parameter //​exception//​ into register ​R0 
-  * copy parameter //addr// into register ​R3+  * copy parameter //addr// into register ​R1
   * branch to compiler specific subroutine //​handleException//​.   * branch to compiler specific subroutine //​handleException//​.
  
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   * Search end of method from addr (end at pattern 0x000000yy)   * Search end of method from addr (end at pattern 0x000000yy)
   * Search exception in exception table at end of method → start < addr < end && exception instanceof type.   * Search exception in exception table at end of method → start < addr < end && exception instanceof type.
-  * If exception is found → put handler address into SRR0, //rfi//.+  * If exception is found → put handler address into PC.
   * If not found →    * If not found → 
-     - get address of call to this method (LR) from stack frame, copy into variable //addr// (in R3).+     - get address of call to this method (LR) from stack frame, copy into variable //addr// (in R1).
      - replace LR in the stack frame with address of //​handleException//​ subroutine.      - replace LR in the stack frame with address of //​handleException//​ subroutine.
      - get address of epilog from exception table and branch to this address, this causes the unwinding of this method.      - get address of epilog from exception table and branch to this address, this causes the unwinding of this method.
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 The figure below gives an example for the handling of exceptions. The figure below gives an example for the handling of exceptions.
-[{{ .:exceptionoverview.png?700 | //Example for handling of exceptions//​}}] ​+[{{ .:exceptionoverviewarm.png?700 | //Example for handling of exceptions//​}}] ​
dev/crosscompiler/backend_arm/exceptions.1565887366.txt.gz · Last modified: 2019/08/15 18:42 by ursgraf