Hi Nick,
Thanks for the reviews!

On Mon, Jul 01, 2024 at 06:40:50PM GMT, Nicholas Piggin wrote:

On Fri Jun 21, 2024 at 4:54 AM AEST, Naveen N Rao wrote:

quoted

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, unless we are using pcrel.

Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Naveen N Rao <naveen@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 14c5ddec3056..ca204f4f21c1 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) && !IS_ENABLED(CONFIG_PPC_KERNEL_PCREL))
+		return offset <= 8;

If it is PCREL, why not offset == 0 as well?

That's handled by the fallback code that is after the above line:
	return !offset;

That addresses both pcrel, as well as 32-bit powerpc.

Thanks,
Naveen