From 540ad5ad05a5945575b154caedfcdc08ed75b810 Mon Sep 17 00:00:00 2001 From: Xiaofeng Yuan Date: Fri, 7 Aug 2026 19:24:29 -0600 Subject: [PATCH] riscv: probes: simulate c.jal instruction 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. Although c.jal is RV32-only, the function compiles unconditionally. On RV64, riscv_insn_is_c_jal() always returns 0, so the simulation code is never invoked and the small overhead in kernel size is acceptable. Signed-off-by: Xiaofeng Yuan Reviewed-by: Charlie Jenkins Tested-by: Charlie Jenkins Reviewed-by: Nam Cao Tested-by: Nam Cao Link: https://patch.msgid.link/20260701081033.49871-2-xiaofengmian@163.com Signed-off-by: Paul Walmsley --- arch/riscv/kernel/probes/decode-insn.c | 2 +- arch/riscv/kernel/probes/simulate-insn.c | 7 +++++++ arch/riscv/kernel/probes/simulate-insn.h | 1 + 3 files changed, 9 insertions(+), 1 deletion(-) diff --git a/arch/riscv/kernel/probes/decode-insn.c b/arch/riscv/kernel/probes/decode-insn.c index 65d9590bfb9f..433d9035b888 100644 --- a/arch/riscv/kernel/probes/decode-insn.c +++ b/arch/riscv/kernel/probes/decode-insn.c @@ -29,12 +29,12 @@ 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); + RISCV_INSN_SET_SIMULATE(c_jal, insn); 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 fa581590c1f8..f8a2f6857877 100644 --- a/arch/riscv/kernel/probes/simulate-insn.c +++ b/arch/riscv/kernel/probes/simulate-insn.c @@ -163,6 +163,13 @@ bool __kprobes simulate_c_j(u32 opcode, unsigned long addr, struct pt_regs *regs return true; } +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); +} + 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 44ebbc444db9..b89e1bb01842 100644 --- a/arch/riscv/kernel/probes/simulate-insn.h +++ b/arch/riscv/kernel/probes/simulate-insn.h @@ -25,6 +25,7 @@ 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); +bool simulate_c_jal(u32 opcode, unsigned long addr, struct pt_regs *regs); 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);