[RFC PATCH 5/9] powerpc/kprobes: Use ftrace to determine if a probe is at function entry

[Naveen N Rao]

Rather than hard-coding the offset into a function to be used to
determine if a kprobe is at function entry, use ftrace_location() to
determine the ftrace location within the function and categorize all
instructions till that offset to be function entry.

For functions that cannot be traced, we fall back to using a fixed
offset of 8 (two instructions) to categorize a probe as being at
function entry for 64-bit elfv2.

Signed-off-by: Naveen N Rao <nav...@kernel.org>
---
 arch/powerpc/kernel/kprobes.c | 18 ++++++++----------
 1 file changed, 8 insertions(+), 10 deletions(-)

diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
index b20ee72e873a..42665dfab59e 100644
--- a/arch/powerpc/kernel/kprobes.c
+++ b/arch/powerpc/kernel/kprobes.c
@@ -105,24 +105,22 @@ kprobe_opcode_t *kprobe_lookup_name(const char *name, 
unsigned int offset)
        return addr;
 }
 
-static bool arch_kprobe_on_func_entry(unsigned long offset)
+static bool arch_kprobe_on_func_entry(unsigned long addr, unsigned long offset)
 {
-#ifdef CONFIG_PPC64_ELF_ABI_V2
-#ifdef CONFIG_KPROBES_ON_FTRACE
-       return offset <= 16;
-#else
-       return offset <= 8;
-#endif
-#else
+       unsigned long ip = ftrace_location(addr);
+
+       if (ip)
+               return offset <= (ip - addr);
+       if (IS_ENABLED(CONFIG_PPC64_ELF_ABI_V2))
+               return offset <= 8;
        return !offset;
-#endif
 }
 
 /* XXX try and fold the magic of kprobe_lookup_name() in this */
 kprobe_opcode_t *arch_adjust_kprobe_addr(unsigned long addr, unsigned long 
offset,
                                         bool *on_func_entry)
 {
-       *on_func_entry = arch_kprobe_on_func_entry(offset);
+       *on_func_entry = arch_kprobe_on_func_entry(addr, offset);
        return (kprobe_opcode_t *)(addr + offset);
 }
 
-- 
2.43.0