Messages in this thread Patch in this message | | | From | "Naveen N. Rao" <> | Subject | [PATCH v4 6/6] powerpc: kprobes: prefer ftrace when probing function entry | Date | Wed, 19 Apr 2017 18:22:28 +0530 |
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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.
Though OPTPROBES provides us with similar performance, we have limited optprobes trampoline slots. As such, when asked to probe at a function entry, default to using the ftrace infrastructure.
With: # cd /sys/kernel/debug/tracing # echo 'p _do_fork' > kprobe_events
before patch: # cat ../kprobes/list c0000000000daf08 k _do_fork+0x8 [DISABLED] c000000000044fc0 k kretprobe_trampoline+0x0 [OPTIMIZED]
and after patch: # cat ../kprobes/list c0000000000d074c k _do_fork+0xc [DISABLED][FTRACE] c0000000000412b0 k kretprobe_trampoline+0x0 [OPTIMIZED]
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com> --- arch/powerpc/kernel/kprobes.c | 17 +++++++++++++++-- 1 file changed, 15 insertions(+), 2 deletions(-)
diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c index df963c6e47b1..d5d6fbd1d788 100644 --- a/arch/powerpc/kernel/kprobes.c +++ b/arch/powerpc/kernel/kprobes.c @@ -49,8 +49,21 @@ kprobe_opcode_t *kprobe_lookup_name(const char *name, unsigned int offset) #ifdef PPC64_ELF_ABI_v2 /* PPC64 ABIv2 needs local entry point */ addr = (kprobe_opcode_t *)kallsyms_lookup_name(name); - if (addr && !offset) - addr = (kprobe_opcode_t *)ppc_function_entry(addr); + if (addr && !offset) { +#ifdef CONFIG_KPROBES_ON_FTRACE + unsigned long faddr; + /* + * Per livepatch.h, ftrace location is always within the first + * 16 bytes of a function on powerpc with -mprofile-kernel. + */ + faddr = ftrace_location_range((unsigned long)addr, + (unsigned long)addr + 16); + if (faddr) + addr = (kprobe_opcode_t *)faddr; + else +#endif + addr = (kprobe_opcode_t *)ppc_function_entry(addr); + } #elif defined(PPC64_ELF_ABI_v1) /* * 64bit powerpc ABIv1 uses function descriptors: -- 2.12.1
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