On Thu, 26 Dec 2019 03:18:07 +0000 Jisheng Zhang wrote: > > > Hi > > On Thu, 26 Dec 2019 11:57:07 +0900 Masami Hiramatsu wrote: > > > > > Hi Jisheng, > > > > On Wed, 25 Dec 2019 09:44:21 +0000 > > Jisheng Zhang <Jisheng.Zhang@xxxxxxxxxxxxx> wrote: > > > > > KPROBES_ON_FTRACE avoids much of the overhead with regular kprobes as it > > > eliminates the need for a trap, as well as the need to emulate or > > > single-step instructions. > > > > > > Tested on berlin arm64 platform. > > > > > > ~ # mount -t debugfs debugfs /sys/kernel/debug/ > > > ~ # cd /sys/kernel/debug/ > > > /sys/kernel/debug # echo 'p _do_fork' > tracing/kprobe_events > > > > > > before the patch: > > > > > > /sys/kernel/debug # cat kprobes/list > > > ffffff801009fe28 k _do_fork+0x0 [DISABLED] > > > > > > after the patch: > > > > > > /sys/kernel/debug # cat kprobes/list > > > ffffff801009ff54 k _do_fork+0x0 [DISABLED][FTRACE] > > > > What happens if user puts a probe on _do_fork+4? > > Is that return -EILSEQ correctly? > > _do_fork+4 can be probed successfully. > > > > > > > > > Signed-off-by: Jisheng Zhang <Jisheng.Zhang@xxxxxxxxxxxxx> > > > --- > > > .../debug/kprobes-on-ftrace/arch-support.txt | 2 +- > > > arch/arm64/Kconfig | 1 + > > > arch/arm64/include/asm/ftrace.h | 1 + > > > arch/arm64/kernel/probes/Makefile | 1 + > > > arch/arm64/kernel/probes/ftrace.c | 78 +++++++++++++++++++ > > > 5 files changed, 82 insertions(+), 1 deletion(-) > > > create mode 100644 arch/arm64/kernel/probes/ftrace.c > > > > > > diff --git a/Documentation/features/debug/kprobes-on-ftrace/arch-support.txt b/Documentation/features/debug/kprobes-on-ftrace/arch-support.txt > > > index 4fae0464ddff..f9dd9dd91e0c 100644 > > > --- a/Documentation/features/debug/kprobes-on-ftrace/arch-support.txt > > > +++ b/Documentation/features/debug/kprobes-on-ftrace/arch-support.txt > > > @@ -9,7 +9,7 @@ > > > | alpha: | TODO | > > > | arc: | TODO | > > > | arm: | TODO | > > > - | arm64: | TODO | > > > + | arm64: | ok | > > > | c6x: | TODO | > > > | csky: | TODO | > > > | h8300: | TODO | > > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > > > index b1b4476ddb83..92b9882889ac 100644 > > > --- a/arch/arm64/Kconfig > > > +++ b/arch/arm64/Kconfig > > > @@ -166,6 +166,7 @@ config ARM64 > > > select HAVE_STACKPROTECTOR > > > select HAVE_SYSCALL_TRACEPOINTS > > > select HAVE_KPROBES > > > + select HAVE_KPROBES_ON_FTRACE > > > select HAVE_KRETPROBES > > > select HAVE_GENERIC_VDSO > > > select IOMMU_DMA if IOMMU_SUPPORT > > > diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h > > > index 91fa4baa1a93..875aeb839654 100644 > > > --- a/arch/arm64/include/asm/ftrace.h > > > +++ b/arch/arm64/include/asm/ftrace.h > > > @@ -20,6 +20,7 @@ > > > > > > /* The BL at the callsite's adjusted rec->ip */ > > > #define MCOUNT_INSN_SIZE AARCH64_INSN_SIZE > > > +#define FTRACE_IP_EXTENSION MCOUNT_INSN_SIZE > > > > > > #define FTRACE_PLT_IDX 0 > > > #define FTRACE_REGS_PLT_IDX 1 > > > diff --git a/arch/arm64/kernel/probes/Makefile b/arch/arm64/kernel/probes/Makefile > > > index 8e4be92e25b1..4020cfc66564 100644 > > > --- a/arch/arm64/kernel/probes/Makefile > > > +++ b/arch/arm64/kernel/probes/Makefile > > > @@ -4,3 +4,4 @@ obj-$(CONFIG_KPROBES) += kprobes.o decode-insn.o \ > > > simulate-insn.o > > > obj-$(CONFIG_UPROBES) += uprobes.o decode-insn.o \ > > > simulate-insn.o > > > +obj-$(CONFIG_KPROBES_ON_FTRACE) += ftrace.o > > > diff --git a/arch/arm64/kernel/probes/ftrace.c b/arch/arm64/kernel/probes/ftrace.c > > > new file mode 100644 > > > index 000000000000..0643aa2dacdb > > > --- /dev/null > > > +++ b/arch/arm64/kernel/probes/ftrace.c > > > @@ -0,0 +1,78 @@ > > > +// SPDX-License-Identifier: GPL-2.0-or-later > > > +/* > > > + * Dynamic Ftrace based Kprobes Optimization > > > + * > > > + * Copyright (C) Hitachi Ltd., 2012 > > > + * Copyright (C) 2019 Jisheng Zhang <jszhang@xxxxxxxxxx> > > > + * Synaptics Incorporated > > > + */ > > > + > > > +#include <linux/kprobes.h> > > > + > > > +/* > > > + * In arm64 FTRACE_WITH_REGS implementation, we patch two nop instructions: > > > + * the lr saver and bl ftrace-entry. Both these instructions are claimed > > > + * by ftrace and we should allow probing on either instruction. > > > > No, the 2nd bl ftrace-entry must not be probed. > > The pair of lr-saver and bl ftrace-entry is tightly coupled. You can not > > decouple it. > > This is the key. different viewing of this results in different implementation. > I'm just wondering why are the two instructions considered as coupled. I think > here we met similar situation as powerpc: https://lkml.org/lkml/2019/6/18/646 > the "mflr r0" equals to lr-saver here, branch to _mcount equals to bl ftrace-entry > could you please kindly comment more? > > Thanks in advance > hmm, I think I may get some part of your opinion. In v7 implementation: if probe on func+4, that's bl ftrace-entry, similar as mcount call on other architectures, we allow this probe as normal. if probe on func+0, the first param ip in kprobe_ftrace_handler() points to func+4(this is adjusted by ftrace), regs->ip points to func+8, so in kprobe_ftrace_handler() we modify regs->ip to func+0 to call kprobe pre handler, then modify regs->ip to func+8 to call kprobe post handler. As can be seen, the first two instructions are considered as a virtual mcount call. From this point of view, lr saver and the bl <ftrace-entry> is coupled. If we split patch3 into two: one to support kprobes func+4 the second to support kprobe on func+0 it would be much clearer. Then the key here is whether we could allow both kprobes on func+0 and func+4 Thanks
