[PATCH v5] riscv: probes: simulate c.jal instruction

[Xiaofeng Yuan]

The c.jal instruction is currently marked REJECTED in kprobes
instruction decoding, but it should be SIMULATED like other
compressed jump instructions.

Add simulate_c_jal() which saves the return address to RA and
sets the program counter to the target offset, reusing
simulate_c_j for the common jump logic.

Since c.jal is RV32-only, guard the implementation with

Signed-off-by: Xiaofeng Yuan <xiaofengmian@xxxxxxx>
#if __riscv_xlen == 32.
---
v4: use regs->ra directly; reorder SET_SIMULATE (per Nam Cao's review)
v5: add #if __riscv_xlen == 32 guard (per Charlie Li's review); removed test case (already provided by Nam Cao)

 arch/riscv/kernel/probes/decode-insn.c   | 4 +++-
 arch/riscv/kernel/probes/simulate-insn.c | 9 +++++++++
 arch/riscv/kernel/probes/simulate-insn.h | 3 +++
 3 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/kernel/probes/decode-insn.c b/arch/riscv/kernel/probes/decode-insn.c
index 65d9590bf..9eb7ead60 100644
--- a/arch/riscv/kernel/probes/decode-insn.c
+++ b/arch/riscv/kernel/probes/decode-insn.c
@@ -29,12 +29,14 @@ riscv_probe_decode_insn(probe_opcode_t *addr, struct arch_probe_insn *api)
 	 * TODO: the REJECTED ones below need to be implemented
 	 */
 #ifdef CONFIG_RISCV_ISA_C
-	RISCV_INSN_REJECTED(c_jal,		insn);
 	RISCV_INSN_REJECTED(c_ebreak,		insn);
 
 	RISCV_INSN_SET_SIMULATE(c_j,		insn);
 	RISCV_INSN_SET_SIMULATE(c_jr,		insn);
 	RISCV_INSN_SET_SIMULATE(c_jalr,		insn);
+#if __riscv_xlen == 32
+	RISCV_INSN_SET_SIMULATE(c_jal,		insn);
+#endif
 	RISCV_INSN_SET_SIMULATE(c_beqz,		insn);
 	RISCV_INSN_SET_SIMULATE(c_bnez,		insn);
 #endif
diff --git a/arch/riscv/kernel/probes/simulate-insn.c b/arch/riscv/kernel/probes/simulate-insn.c
index fa581590c..907598b61 100644
--- a/arch/riscv/kernel/probes/simulate-insn.c
+++ b/arch/riscv/kernel/probes/simulate-insn.c
@@ -163,6 +163,15 @@ bool __kprobes simulate_c_j(u32 opcode, unsigned long addr, struct pt_regs *regs
 	return true;
 }
 
+#if __riscv_xlen == 32
+bool __kprobes simulate_c_jal(u32 opcode, unsigned long addr, struct pt_regs *regs)
+{
+	regs->ra = addr + 2;
+
+	return simulate_c_j(opcode, addr, regs);
+}
+#endif
+
 static bool __kprobes simulate_c_jr_jalr(u32 opcode, unsigned long addr, struct pt_regs *regs,
 					 bool is_jalr)
 {
diff --git a/arch/riscv/kernel/probes/simulate-insn.h b/arch/riscv/kernel/probes/simulate-insn.h
index 44ebbc444..6b3b510b5 100644
--- a/arch/riscv/kernel/probes/simulate-insn.h
+++ b/arch/riscv/kernel/probes/simulate-insn.h
@@ -25,6 +25,9 @@ bool simulate_branch(u32 opcode, unsigned long addr, struct pt_regs *regs);
 bool simulate_jal(u32 opcode, unsigned long addr, struct pt_regs *regs);
 bool simulate_jalr(u32 opcode, unsigned long addr, struct pt_regs *regs);
 bool simulate_c_j(u32 opcode, unsigned long addr, struct pt_regs *regs);
+#if __riscv_xlen == 32
+bool simulate_c_jal(u32 opcode, unsigned long addr, struct pt_regs *regs);
+#endif
 bool simulate_c_jr(u32 opcode, unsigned long addr, struct pt_regs *regs);
 bool simulate_c_jalr(u32 opcode, unsigned long addr, struct pt_regs *regs);
 bool simulate_c_bnez(u32 opcode, unsigned long addr, struct pt_regs *regs);
-- 
2.43.0