Re: [patch/RFA] multiarch INSTRUCTION_NULLIFIED

Randolph Chung
2004-12-01T16:25:43Z

In-Reply-To: <BDD32F47.81A3%schlie@comcast.net>

> A point that may be worth considering is that on architectures which support
> jump/branch delay slots, the branch and delay slot is actually logically
> executed as single compound instruction, treated by the machine as a unified
> whole.

i don't think this is true for hppa. for instance you can do a hardware
singlestep into the delay slot of a branch insn by setting the recovery
counter appropriately. this will cause an hardware interruption which
the kernel can translate to a SIGTRAP.

nullification is also a more general concept on hppa which doesn't only
apply to branch instructions. A lot of ALU instructions can also
conditioanlly nullify the next insn, which potentially could belong to a
different line of source code. gcc uses this to implement if-conversion,
for example.

randolph
--
Randolph Chung
Debian GNU/Linux Developer, hppa/ia64 ports