linux-kernel - [RFC PATCH v4 02/17] powerpc/kprobes: Use ftrace to determine if a probe is at function entry

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Message-ID: <dc9bea437809e4c0dbb6dba2e23325eb83a770d0.1720942106.git.naveen@kernel.org>
Date: Sun, 14 Jul 2024 13:57:38 +0530
From: Naveen N Rao <naveen@...nel.org>
To: <linuxppc-dev@...ts.ozlabs.org>,
	<linux-trace-kernel@...r.kernel.org>,
	<bpf@...r.kernel.org>,
	linux-kbuild@...r.kernel.org,
	<linux-kernel@...r.kernel.org>
Cc: Michael Ellerman <mpe@...erman.id.au>,
	Nicholas Piggin <npiggin@...il.com>,
	Christophe Leroy <christophe.leroy@...roup.eu>,
	Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Andrii Nakryiko <andrii@...nel.org>,
	Masahiro Yamada <masahiroy@...nel.org>,
	Hari Bathini <hbathini@...ux.ibm.com>,
	Mahesh Salgaonkar <mahesh@...ux.ibm.com>,
	Vishal Chourasia <vishalc@...ux.ibm.com>
Subject: [RFC PATCH v4 02/17] 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, unless we are using pcrel.

Acked-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
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 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;
 	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);
 }
 
-- 
2.45.2