Re: [PATCH RFC 2/7] powerpc: Change analyse_instr so it doesn't modify *regs

[Michael Neuling <mikey@neuling.org>]

On Wed, 2017-08-23 at 09:47 +1000, Paul Mackerras wrote:
> The analyse_instr function currently doesn't just work out what an
> instruction does, it also executes those instructions whose effect
> is only to update CPU registers that are stored in struct pt_regs.
> This is undesirable because optprobes uses analyse_instr to work out
> if an instruction could be successfully emulated in future.
>=20
> This changes analyse_instr so it doesn't modify *regs; instead it
> stores information in the instruction_op structure to indicate what
> registers (GPRs, CR, XER, LR) would be set and what value they would
> be set to.=C2=A0=C2=A0A companion function called emulate_update_regs() c=
an
> then use that information to update a pt_regs struct appropriately.
>=20
> As a minor cleanup, this replaces inline asm using the cntlzw and
> cntlzd instructions with calls to __builtin_clz() and __builtin_clzl().

+1 ! This is super useful!

As mentioned offline, this clashes with the recent changes to sstep.c in po=
werpc
next.  In fact, the new instructions added there need to have these changes
applied.

Mikey