| Message ID | 53ebcc66e4a7ccf1c22cd1703afb0e4738f981ea.1492606062.git.naveen.n.rao@linux.vnet.ibm.com (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 24bd909e94776ecce95291bff910f14c78ac4a43 |
| Headers | show |
On Wed, 2017-04-19 at 12:52:28 UTC, "Naveen N. Rao" 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. > > 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> Applied to powerpc next, thanks. https://git.kernel.org/powerpc/c/24bd909e94776ecce95291bff910f1 cheers
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:
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(-)