breakpoint extension for remote protocol, take II

J.T. Conklin
Mon Jun 14 17:43:00 GMT 1999

>>>>> "Toshiyasu" == Toshiyasu Morita <> writes:
>> I was unaware processors with multiple software breakpoints
>> existed.  I assume that the 2 byte breakpoint instructions have to
>> be inserted in "high-density" code segments and 4 byte breakpoints
>> insns have to be inserted in "low-density" segments.

Toshiyasu> Is there a four-byte sequence which is an illegal
Toshiyasu> instruction in both MIPS16 and MIPS32 modes?

Even if there were, I don't think it would work.

If you installed this four byte sequence in a 16 bit code segment at
0x1000, it would also overwrite the instruction at 0x1002.  If that
instruction is a branch target, bad things are likely to happen.  A
bit of compiler support to insert a nop before branch targets could
possibly make this work, but that would diminish any benefit high
density instructions are supposed to offer.


J.T. Conklin
RedBack Networks

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