diff options
| author | Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com> | 2017-04-19 18:22:28 +0530 |
|---|---|---|
| committer | Michael Ellerman <mpe@ellerman.id.au> | 2017-04-24 19:07:59 +1000 |
| commit | 24bd909e94776ecce95291bff910f14c78ac4a43 (patch) | |
| tree | 8b491fb94a15ec8b9b5c727e02e8acfced7a3106 | |
| parent | 1b32cd1715378c9a3856df4a80920f8e241f914c (diff) | |
powerpc/kprobes: Prefer ftrace when probing function entry
KPROBES_ON_FTRACE avoids much of the overhead of 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>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
| -rw-r--r-- | arch/powerpc/kernel/kprobes.c | 17 |
1 files changed, 15 insertions, 2 deletions
diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c index 50aabf819787..ca040e1be892 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: |