Re: [PATCH v4.2] powerpc/modules: Don't try to restore r2 after a sibling call
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@linux.vnet.ibm.com> 8< From: Josh Poimboeuf <jpoim...@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 3c82 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 <jpoim...@redhat.com> Reviewed-and-tested-by: Kamalesh Babulal <kamal...@linux.vnet.ibm.com> Thanks, Kamalesh! - Naveen
Re: [PATCH v4.2] powerpc/modules: Don't try to restore r2 after a sibling call
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 ----8<---- From: Josh Poimboeuf 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 3c82 The error was triggered by the following code in unregister_netdevice_queue(): 14c: 00 00 00 48 b 14c 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 Reviewed-and-tested-by: Kamalesh Babulal Thanks, Kamalesh! - Naveen
Re: [PATCH v4.2] powerpc/modules: Don't try to restore r2 after a sibling call
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 <jpoim...@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 3c82 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 <jpoim...@redhat.com> Reviewed-and-tested-by: Kamalesh Babulal <kamal...@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;
Re: [PATCH v4.2] powerpc/modules: Don't try to restore r2 after a sibling call
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 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 3c82 The error was triggered by the following code in unregister_netdevice_queue(): 14c: 00 00 00 48 b 14c 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 Reviewed-and-tested-by: Kamalesh Babulal --- 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;
[PATCH v4.2] powerpc/modules: Don't try to restore r2 after a sibling call
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 <jpoim...@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 3c82 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 <jpoim...@redhat.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; -- 2.13.6
[PATCH v4.2] powerpc/modules: Don't try to restore r2 after a sibling call
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 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 3c82 The error was triggered by the following code in unregister_netdevice_queue(): 14c: 00 00 00 48 b 14c 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 --- 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; -- 2.13.6