Message ID | 20171116174537.duz4x6vfzhp44lfh@treble (mailing list archive) |
---|---|
State | Accepted |
Commit | b9eab08d012fa093947b230f9a87257c27fb829b |
Headers | show |
Series | [v4.2] powerpc/modules: Don't try to restore r2 after a sibling call | expand |
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 ;-) > >> 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? > > ----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> > --- > arch/powerpc/include/asm/code-patching.h | 1 + > arch/powerpc/kernel/module_64.c | 12 +++++++++++- > arch/powerpc/lib/code-patching.c | 5 +++++ > 3 files changed, 17 insertions(+), 1 deletion(-) > > diff --git a/arch/powerpc/include/asm/code-patching.h b/arch/powerpc/include/asm/code-patching.h > index abef812de7f8..2c895e8d07f7 100644 > --- a/arch/powerpc/include/asm/code-patching.h > +++ b/arch/powerpc/include/asm/code-patching.h > @@ -33,6 +33,7 @@ int patch_branch(unsigned int *addr, unsigned long target, int flags); > int patch_instruction(unsigned int *addr, unsigned int instr); > > int instr_is_relative_branch(unsigned int instr); > +int instr_is_relative_link_branch(unsigned int instr); > int instr_is_branch_to_addr(const unsigned int *instr, unsigned long addr); > unsigned long branch_target(const unsigned int *instr); > unsigned int translate_branch(const unsigned int *dest, > diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c > index 759104b99f9f..180c16f04063 100644 > --- a/arch/powerpc/kernel/module_64.c > +++ b/arch/powerpc/kernel/module_64.c > @@ -487,7 +487,17 @@ static bool is_early_mcount_callsite(u32 *instruction) > restore r2. */ > static int restore_r2(u32 *instruction, struct module *me) > { > - if (is_early_mcount_callsite(instruction - 1)) > + u32 *prev_insn = instruction - 1; > + > + if (is_early_mcount_callsite(prev_insn)) > + return 1; > + > + /* > + * Make sure the branch isn't a sibling call. Sibling calls aren't > + * "link" branches and they don't return, so they don't need the r2 > + * restore afterwards. > + */ > + if (!instr_is_relative_link_branch(*prev_insn)) > return 1; > > if (*instruction != PPC_INST_NOP) { > diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c > index c9de03e0c1f1..d81aab7441f7 100644 > --- a/arch/powerpc/lib/code-patching.c > +++ b/arch/powerpc/lib/code-patching.c > @@ -304,6 +304,11 @@ int instr_is_relative_branch(unsigned int instr) > return instr_is_branch_iform(instr) || instr_is_branch_bform(instr); > } > > +int instr_is_relative_link_branch(unsigned int instr) > +{ > + return instr_is_relative_branch(instr) && (instr & BRANCH_SET_LINK); > +} > + > static unsigned long branch_iform_target(const unsigned int *instr) > { > signed long imm; >
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
On Thu, 2017-11-16 at 17:45:37 UTC, Josh Poimboeuf wrote: > > 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> > Acked-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com> Applied to powerpc next, thanks. https://git.kernel.org/powerpc/c/b9eab08d012fa093947b230f9a8725 cheers
diff --git a/arch/powerpc/include/asm/code-patching.h b/arch/powerpc/include/asm/code-patching.h index abef812de7f8..2c895e8d07f7 100644 --- a/arch/powerpc/include/asm/code-patching.h +++ b/arch/powerpc/include/asm/code-patching.h @@ -33,6 +33,7 @@ int patch_branch(unsigned int *addr, unsigned long target, int flags); int patch_instruction(unsigned int *addr, unsigned int instr); int instr_is_relative_branch(unsigned int instr); +int instr_is_relative_link_branch(unsigned int instr); int instr_is_branch_to_addr(const unsigned int *instr, unsigned long addr); unsigned long branch_target(const unsigned int *instr); unsigned int translate_branch(const unsigned int *dest, diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c index 759104b99f9f..180c16f04063 100644 --- a/arch/powerpc/kernel/module_64.c +++ b/arch/powerpc/kernel/module_64.c @@ -487,7 +487,17 @@ static bool is_early_mcount_callsite(u32 *instruction) restore r2. */ static int restore_r2(u32 *instruction, struct module *me) { - if (is_early_mcount_callsite(instruction - 1)) + u32 *prev_insn = instruction - 1; + + if (is_early_mcount_callsite(prev_insn)) + return 1; + + /* + * Make sure the branch isn't a sibling call. Sibling calls aren't + * "link" branches and they don't return, so they don't need the r2 + * restore afterwards. + */ + if (!instr_is_relative_link_branch(*prev_insn)) return 1; if (*instruction != PPC_INST_NOP) { diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c index c9de03e0c1f1..d81aab7441f7 100644 --- a/arch/powerpc/lib/code-patching.c +++ b/arch/powerpc/lib/code-patching.c @@ -304,6 +304,11 @@ int instr_is_relative_branch(unsigned int instr) return instr_is_branch_iform(instr) || instr_is_branch_bform(instr); } +int instr_is_relative_link_branch(unsigned int instr) +{ + return instr_is_relative_branch(instr) && (instr & BRANCH_SET_LINK); +} + static unsigned long branch_iform_target(const unsigned int *instr) { signed long imm;