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....@linux.vnet.ibm.com>
---
arch/powerpc/include/asm/kprobes.h | 20 ++++++++++++++++++++
1 file changed, 20 insertions(+)
diff --git a/arch/powerpc/include/asm/kprobes.h
b/arch/powerpc/include/asm/kprobes.h
index 3305a12286fa..09e74edee625 100644
--- a/arch/powerpc/include/asm/kprobes.h
+++ b/arch/powerpc/include/asm/kprobes.h
@@ -60,12 +60,32 @@ extern kprobe_opcode_t optprobe_template_end[];
#ifdef PPC64_ELF_ABI_v2
/* PPC64 ABIv2 needs local entry point */
+#ifdef CONFIG_KPROBES_ON_FTRACE
+/*
+ * Per livepatch.h, ftrace location is always within the first 16 bytes
+ * of a function on powerpc with -mprofile-kernel.
+ */
+#define kprobe_lookup_name(name, addr, offset) \
+{ \
+ addr = (kprobe_opcode_t *)kallsyms_lookup_name(name); \
+ if (addr && !(offset)) { \
+ unsigned long faddr; \
+ faddr = ftrace_location_range((unsigned long)addr, \
+ (unsigned long)addr + 16);\
+ if (faddr) \
+ addr = (kprobe_opcode_t *)faddr; \
+ else \
+ addr = (kprobe_opcode_t *)ppc_function_entry(addr);
\
+ } \
+}
+#else
#define kprobe_lookup_name(name, addr, offset) \
{ \
addr = (kprobe_opcode_t *)kallsyms_lookup_name(name); \
if (addr && !(offset)) \
addr = (kprobe_opcode_t *)ppc_function_entry(addr); \
}
+#endif
#elif defined(PPC64_ELF_ABI_v1)
/*
* 64bit powerpc ABIv1 uses function descriptors:
--
2.11.0
