linux-kernel - [PATCH 2/7] arm64: probes: Break ret out from bl/blr

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Message-ID: <20250318204841.373116-3-jeremy.linton@arm.com>
Date: Tue, 18 Mar 2025 15:48:36 -0500
From: Jeremy Linton <jeremy.linton@....com>
To: linux-trace-kernel@...r.kernel.org
Cc: linux-perf-users@...r.kernel.org,
	mhiramat@...nel.org,
	oleg@...hat.com,
	peterz@...radead.org,
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	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	Jeremy Linton <jeremy.linton@....com>
Subject: [PATCH 2/7] arm64: probes: Break ret out from bl/blr

Prepare for GCS by breaking RET out into its own function, where
it makes more sense to encapsulate the new behavior independent
from the branch instructions.

Signed-off-by: Jeremy Linton <jeremy.linton@....com>
---
 arch/arm64/kernel/probes/decode-insn.c   |  7 ++++---
 arch/arm64/kernel/probes/simulate-insn.c | 10 +++++++++-
 arch/arm64/kernel/probes/simulate-insn.h |  3 ++-
 3 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/kernel/probes/decode-insn.c b/arch/arm64/kernel/probes/decode-insn.c
index 6438bf62e753..4137cc5ef031 100644
--- a/arch/arm64/kernel/probes/decode-insn.c
+++ b/arch/arm64/kernel/probes/decode-insn.c
@@ -108,9 +108,10 @@ arm_probe_decode_insn(u32 insn, struct arch_probe_insn *api)
 	    aarch64_insn_is_bl(insn)) {
 		api->handler = simulate_b_bl;
 	} else if (aarch64_insn_is_br(insn) ||
-	    aarch64_insn_is_blr(insn) ||
-	    aarch64_insn_is_ret(insn)) {
-		api->handler = simulate_br_blr_ret;
+		aarch64_insn_is_blr(insn)) {
+		api->handler = simulate_br_blr;
+	} else if (aarch64_insn_is_ret(insn)) {
+		api->handler = simulate_ret;
 	} else {
 		/*
 		 * Instruction cannot be stepped out-of-line and we don't
diff --git a/arch/arm64/kernel/probes/simulate-insn.c b/arch/arm64/kernel/probes/simulate-insn.c
index 4c6d2d712fbd..09a0b36122d0 100644
--- a/arch/arm64/kernel/probes/simulate-insn.c
+++ b/arch/arm64/kernel/probes/simulate-insn.c
@@ -126,7 +126,7 @@ simulate_b_cond(u32 opcode, long addr, struct pt_regs *regs)
 }
 
 void __kprobes
-simulate_br_blr_ret(u32 opcode, long addr, struct pt_regs *regs)
+simulate_br_blr(u32 opcode, long addr, struct pt_regs *regs)
 {
 	int xn = (opcode >> 5) & 0x1f;
 
@@ -138,6 +138,14 @@ simulate_br_blr_ret(u32 opcode, long addr, struct pt_regs *regs)
 		set_x_reg(regs, 30, addr + 4);
 }
 
+void __kprobes
+simulate_ret(u32 opcode, long addr, struct pt_regs *regs)
+{
+	int xn = (opcode >> 5) & 0x1f;
+
+	instruction_pointer_set(regs, get_x_reg(regs, xn));
+}
+
 void __kprobes
 simulate_cbz_cbnz(u32 opcode, long addr, struct pt_regs *regs)
 {
diff --git a/arch/arm64/kernel/probes/simulate-insn.h b/arch/arm64/kernel/probes/simulate-insn.h
index efb2803ec943..9e772a292d56 100644
--- a/arch/arm64/kernel/probes/simulate-insn.h
+++ b/arch/arm64/kernel/probes/simulate-insn.h
@@ -11,7 +11,8 @@
 void simulate_adr_adrp(u32 opcode, long addr, struct pt_regs *regs);
 void simulate_b_bl(u32 opcode, long addr, struct pt_regs *regs);
 void simulate_b_cond(u32 opcode, long addr, struct pt_regs *regs);
-void simulate_br_blr_ret(u32 opcode, long addr, struct pt_regs *regs);
+void simulate_br_blr(u32 opcode, long addr, struct pt_regs *regs);
+void simulate_ret(u32 opcode, long addr, struct pt_regs *regs);
 void simulate_cbz_cbnz(u32 opcode, long addr, struct pt_regs *regs);
 void simulate_tbz_tbnz(u32 opcode, long addr, struct pt_regs *regs);
 void simulate_ldr_literal(u32 opcode, long addr, struct pt_regs *regs);
-- 
2.48.1