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

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Message-ID: <15f0b3a2e72326423cfb4ce4e89afff540042245.1702045299.git.naveen@kernel.org>
Date:   Fri,  8 Dec 2023 22:00:44 +0530
From:   Naveen N Rao <naveen@...nel.org>
To:     <linuxppc-dev@...ts.ozlabs.org>, <linux-kernel@...r.kernel.org>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Nicholas Piggin <npiggin@...il.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        "Aneesh Kumar K.V" <aneesh.kumar@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Mark Rutland <mark.rutland@....com>,
        Florent Revest <revest@...omium.org>,
        Masami Hiramatsu <mhiramat@...nel.org>
Subject: [RFC PATCH 5/9] powerpc/kprobes: Use ftrace to determine if a probe is at function entry

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 <naveen@...nel.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