Exception Handling Support

EH_RETURN_DATA_REGNO (N)

A C expression whose value is the Nth register number used for data by exception handlers, or INVALID_REGNUM if fewer than N registers are usable.

The exception handling library routines communicate with the exception handlers via a set of agreed upon registers. Ideally these registers should be call-clobbered; it is possible to use call-saved registers, but may negatively impact code size. The target must support at least 2 data registers, but should define 4 if there are enough free registers.

You must define this macro if you want to support call frame exception handling like that provided by DWARF 2.

EH_RETURN_STACKADJ_RTX

A C expression whose value is RTL representing a location in which to store a stack adjustment to be applied before function return. This is used to unwind the stack to an exception handler's call frame. It will be assigned zero on code paths that return normally.

Typically this is a call-clobbered hard register that is otherwise untouched by the epilogue, but could also be a stack slot.

You must define this macro if you want to support call frame exception handling like that provided by DWARF 2.

EH_RETURN_HANDLER_RTX

A C expression whose value is RTL representing a location in which to store the address of an exception handler to which we should return. It will not be assigned on code paths that return normally.

Typically this is the location in the call frame at which the normal return address is stored. For targets that return by popping an address off the stack, this might be a memory address just below the target call frame rather than inside the current call frame. EH_RETURN_STACKADJ_RTX will have already been assigned, so it may be used to calculate the location of the target call frame.

Some targets have more complex requirements than storing to an address calculable during initial code generation. In that case the eh_return instruction pattern should be used instead.

If you want to support call frame exception handling, you must define either this macro or the eh_return instruction pattern.

ASM_PREFERRED_EH_DATA_FORMAT(code, global)

This macro chooses the encoding of pointers embedded in the exception handling sections. If at all possible, this should be defined such that the exception handling section will not require dynamic relocations, and so may be read-only.

code is 0 for data, 1 for code labels, 2 for function pointers. global is true if the symbol may be affected by dynamic relocations. The macro should return a combination of the DW_EH_PE_* defines as found in dwarf2.h.

If this macro is not defined, pointers will not be encoded but represented directly.

ASM_MAYBE_OUTPUT_ENCODED_ADDR_RTX(file, encoding, size, addr, done)

This macro allows the target to emit whatever special magic is required to represent the encoding chosen by ASM_PREFERRED_EH_DATA_FORMAT. Generic code takes care of pc-relative and indirect encodings; this must be defined if the target uses text-relative or data-relative encodings.

This is a C statement that branches to done if the format was handled. encoding is the format chosen, size is the number of bytes that the format occupies, addr is the SYMBOL_REF to be emitted.

MD_FALLBACK_FRAME_STATE_FOR(context, fs, success)

This macro allows the target to add cpu and operating system specific code to the call-frame unwinder for use when there is no unwind data available. The most common reason to implement this macro is to unwind through signal frames.

This macro is called from uw_frame_state_for in unwind-dw2.c and unwind-ia64.c. context is an _Unwind_Context; fs is an _Unwind_FrameState. Examine context->ra for the address of the code being executed and context->cfa for the stack pointer value. If the frame can be decoded, the register save addresses should be updated in fs and the macro should branch to success. If the frame cannot be decoded, the macro should do nothing.