dev:crosscompiler:backend_arm:exceptions
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| Both sides previous revisionPrevious revisionNext revision | Previous revisionNext revisionBoth sides next revision | ||
| dev:crosscompiler:backend_arm:exceptions [2019/08/05 17:49] – [Java Exceptions] ursgraf | dev:crosscompiler:backend_arm:exceptions [2019/08/23 16:58] – [Java Exceptions] ursgraf | ||
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| ===== Java Exceptions ===== | ===== Java Exceptions ===== | ||
| - | ==== Program | + | ==== Supervisor Call Exception ==== |
| - | Each Java exception causes a ARM program | + | 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 SRR0. | + | * Get address of causing instruction into variable //addr// from LR. Must happen first, as the next step uses LR as scratch register. |
| - | * Read instruction at this address | + | * increment counter |
| - | * Determine from type of instruction which kind of exception was thrown | + | * Read instruction at this address |
| + | * Determine from immediate value of instruction which kind of exception was thrown | ||
| * If unchecked instruction: | * If unchecked instruction: | ||
| - | * copy parameter // | + | * copy parameter // |
| - | * copy parameter //addr// into register | + | * copy parameter //addr// into register |
| * branch to compiler specific subroutine // | * branch to compiler specific subroutine // | ||
| + | |||
| + | The supervisor call handler can use volatile registers freely. It further uses a few nonvolatile registers. However, these must be saved onto the stack at the start of the method and must be restored at the end. | ||
| ==== Subroutine handleException ==== | ==== Subroutine handleException ==== | ||
| Line 34: | Line 37: | ||
| * 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 // | - replace LR in the stack frame with address of // | ||
| - 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. | ||
dev/crosscompiler/backend_arm/exceptions.txt · Last modified: 2019/11/17 18:24 by ursgraf
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