Messages in this thread | | | Date | Sat, 18 Nov 2017 14:03:36 +0530 | From | "Naveen N. Rao" <> | Subject | Re: [PATCH v4.2] powerpc/modules: Don't try to restore r2 after a sibling call |
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Kamalesh Babulal wrote: > On Thursday 16 November 2017 11:15 PM, Josh Poimboeuf wrote: >> On Thu, Nov 16, 2017 at 06:39:03PM +0530, Naveen N. Rao wrote: >>> Josh Poimboeuf wrote: >>>> On Wed, Nov 15, 2017 at 02:58:33PM +0530, Naveen N. Rao wrote: >>>>>> +int instr_is_link_branch(unsigned int instr) >>>>>> +{ >>>>>> + return (instr_is_branch_iform(instr) || instr_is_branch_bform(instr)) && >>>>>> + (instr & BRANCH_SET_LINK); >>>>>> +} >>>>>> + >>>>> >>>>> Nitpicking here, but since we're not considering the other branch forms, >>>>> perhaps this can be renamed to instr_is_link_relative_branch() (or maybe >>>>> instr_is_relative_branch_link()), just so we're clear :) >>>> >>>> My understanding is that the absolute/relative bit isn't a "form", but >>>> rather a bit that can be set for either the b-form (conditional) or the >>>> i-form (unconditional). And the above function isn't checking the >>>> absolute bit, so it isn't necessarily a relative branch. Or did I miss >>>> something? >>> >>> Ah, good point. I was coming from the fact that we are only considering the >>> i-form and b-form branches and not the lr/ctr/tar based branches, which are >>> always absolute branches, but can also set the link register. >> >> Hm, RISC is more complicated than I realized ;-)
As long as 'RISC' gets people to take a look ;D
>> >>> Thinking about this more, aren't we only interested in relative branches >>> here (for relocations), so can we actually filter out the absolute branches? >>> Something like this? >>> >>> int instr_is_relative_branch_link(unsigned int instr) >>> { >>> return ((instr_is_branch_iform(instr) || instr_is_branch_bform(instr)) && >>> !(instr & BRANCH_ABSOLUTE) && (instr & BRANCH_SET_LINK)); >> >> Yeah, makes sense to me. Here's another try (also untested). If this >> looks ok, Kamalesh would you mind testing again?
Thanks. That looks good to me. Acked-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
>> >> ----8<---- >> >> From: Josh Poimboeuf <jpoimboe@redhat.com> >> Subject: [PATCH v4.2] powerpc/modules: Don't try to restore r2 after a sibling call >> >> When attempting to load a livepatch module, I got the following error: >> >> module_64: patch_module: Expect noop after relocate, got 3c820000 >> >> The error was triggered by the following code in >> unregister_netdevice_queue(): >> >> 14c: 00 00 00 48 b 14c <unregister_netdevice_queue+0x14c> >> 14c: R_PPC64_REL24 net_set_todo >> 150: 00 00 82 3c addis r4,r2,0 >> >> GCC didn't insert a nop after the branch to net_set_todo() because it's >> a sibling call, so it never returns. The nop isn't needed after the >> branch in that case. >> >> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> > > Reviewed-and-tested-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Thanks, Kamalesh!
- Naveen
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