dev:crosscompiler:backend_arm:exceptions
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| dev:crosscompiler:backend_arm:exceptions [2019/08/05 09:32] – [ARM Exceptions] ursgraf | dev:crosscompiler:backend_arm:exceptions [2019/08/15 18:42] – [Java Exceptions] ursgraf | ||
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| ===== Java Exceptions ===== | ===== Java Exceptions ===== | ||
| - | ==== Program | + | ==== 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: | ||
| + | * 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 | ||
| + | * Determine from immediate value of instruction which kind of exception was thrown | ||
| + | * If unchecked instruction: | ||
| + | * copy parameter // | ||
| + | * copy parameter //addr// into register R3 | ||
| + | * 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 ==== | ||
| + | The following steps have to be taken: | ||
| + | * 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. | ||
| + | * If exception is found → put handler address into SRR0, //rfi//. | ||
| + | * If not found → | ||
| + | - get address of call to this method (LR) from stack frame, copy into variable //addr// (in R3). | ||
| + | - 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. | ||
| + | |||
| + | When the unwinding of a method is done, the flow of control automatically returns to // | ||
| + | |||
| + | The figure below gives an example for the handling of exceptions. | ||
| + | [{{ .: | ||
dev/crosscompiler/backend_arm/exceptions.txt · Last modified: 2019/11/17 18:24 by ursgraf
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