Messages in this thread | | | Date | Tue, 12 Jun 2012 10:22:22 +0530 | From | Ananth N Mavinakayanahalli <> | Subject | Re: [PATCH 2/2] [POWERPC] uprobes: powerpc port |
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On Tue, Jun 12, 2012 at 02:01:46PM +1000, Michael Ellerman wrote: > On Fri, 2012-06-08 at 14:51 +0530, Ananth N Mavinakayanahalli wrote: > > On Fri, Jun 08, 2012 at 04:38:17PM +1000, Michael Ellerman wrote: > > > On Fri, 2012-06-08 at 11:49 +0530, Ananth N Mavinakayanahalli wrote: > > > > On Fri, Jun 08, 2012 at 04:17:44PM +1000, Michael Ellerman wrote: > > > > > On Fri, 2012-06-08 at 11:31 +0530, Ananth N Mavinakayanahalli wrote: > > > > > > On Fri, Jun 08, 2012 at 03:51:54PM +1000, Michael Ellerman wrote: > > > > > > > On Fri, 2012-06-08 at 10:06 +0530, Ananth N Mavinakayanahalli wrote: > > > > > > > > > > > > But MSR_PR=1 and hence emulate_step() will return -1 and hence we will > > > > > > end up single-stepping using user_enable_single_step(). Same with rfid. > > > > > > > > > > Right. But that was exactly Jim's point, you may be asked to emulate > > > > > those instructions even though you wouldn't expect to see them in > > > > > userspace code, so you need to handle it. > > > > > > > > > > Luckily it looks like emulate_step() will do the right thing for you. > > > > > It'd be good to test it to make 100% sure. > > > > > > > > Sure. Will add that check and send v2. > > > > > > Sorry I didn't mean add a test in the code, I meant construct a test > > > case to confirm that it works as expected. > > > > Michael, > > > > I just hand-coded the instr to emulate_step() and here are the results: > > > > MSR_PR is set > > insn = 7c600124, ret = 0 /* mtmsr */ > > insn = 7c600164, ret = 0 /* mtmsrd */ > > insn = 4c000024, ret = -1 /* rfid */ > > insn = 4c000064, ret = 0 /* rfi */ > > > > Also verified that standalone programs with those instructions in inline > > asm will die with a SIGILL. > > > > So, for mtmsr, mtmsrd and rfi, we have to single-step them which will > > result in a SIGILL in turn. > > What happens in the rfid case? You don't handle -1 from emulate_step() > any differently AFAICS, so don't we try to single step that too?
-1 is just emulate_step() flagging cases where instructions must not be single-stepped (rfi[d], mtmsr that clears MSR_RI). But as with the other OEA instructions in user space, we fail with a SIGILL.
As the application is hozed in any case if we encounter an OEA instruction, I'd think there is no point in handling a -1 from emulate_step() any differently.
Ananth
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