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Subject[PATCH -next 1/2] riscv: implemented auipc simulate instruction
Date
To test the kprobe-based event tracing, we prepare
a kernel module 'kprobe_test.ko' to add the probes.
The assembly codes (partially) of the module are as follows:
...
0000000000000000 <kprobe_test_branch>:
...
0000000000000038 <.LVL1>:
38: 00000597 auipc a1,0x0
3c: 00058593 mv a1,a1
...

Test the kprobe-based event tracing in qemu-system-riscv64:
First, install the kprobe test module:
insmod /root/kprobe_test.ko

Then, add a probe as a new event at an 'auipc' instruction,
the following error occurs due to the instruction not allowed to probe yet:
echo "p:auipc kprobe_test:kprobe_test_branch+0x38 epc=%epc opcode=+0(%epc):x32" >> /sys/kernel/debug/tracing/kprobe_events
sh: write error: Invalid argument

This patch implemented the 'auipc' simulate instruction and allowed to probe it.
Merge this patch and perform the test again, the test results are as follows:
First, add a probe at the 'auipc' instruction:
echo "p:auipc kprobe_test:kprobe_test_branch+0x38 epc=%epc opcode=+0(%epc):x32" >> /sys/kernel/debug/tracing/kprobe_events
echo 1 > /sys/kernel/debug/tracing/events/kprobes/auipc/enable

Then, do something to run to the probe.
After that, see the traced information:
cat /sys/kernel/debug/tracing/trace
sysctl-58 [001] d... 179.126350: auipc: (kprobe_test_branch+0x38/0x10e [kprobe_test]) epc=0xffffffff016122aa opcode=0x100073

Now we can see the traced information.
The actual address of the symbol 'kprobe_test_branch' is as follows:
cat /proc/kallsyms | grep kprobe_test_branch
ffffffff01612272 t kprobe_test_branch [kprobe_test]

Based on the traced information and the actual address of the symbol
'kprobe_test_branch', we can also see that the 'auipc' instruction
has been replaced by 'ebreak(0x100073)' instruction.

--------

Signed-off-by: Chen Lifu <chenlifu@huawei.com>
---
arch/riscv/kernel/probes/decode-insn.c | 2 +-
arch/riscv/kernel/probes/simulate-insn.c | 34 ++++++++++++++++++++++++
2 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/kernel/probes/decode-insn.c b/arch/riscv/kernel/probes/decode-insn.c
index 0ed043acc882..5eb03fb61450 100644
--- a/arch/riscv/kernel/probes/decode-insn.c
+++ b/arch/riscv/kernel/probes/decode-insn.c
@@ -38,11 +38,11 @@ riscv_probe_decode_insn(probe_opcode_t *addr, struct arch_probe_insn *api)
RISCV_INSN_REJECTED(c_ebreak, insn);
#endif

- RISCV_INSN_REJECTED(auipc, insn);
RISCV_INSN_REJECTED(branch, insn);

RISCV_INSN_SET_SIMULATE(jal, insn);
RISCV_INSN_SET_SIMULATE(jalr, insn);
+ RISCV_INSN_SET_SIMULATE(auipc, insn);

return INSN_GOOD;
}
diff --git a/arch/riscv/kernel/probes/simulate-insn.c b/arch/riscv/kernel/probes/simulate-insn.c
index 2519ce26377d..b81719522d5c 100644
--- a/arch/riscv/kernel/probes/simulate-insn.c
+++ b/arch/riscv/kernel/probes/simulate-insn.c
@@ -83,3 +83,37 @@ bool __kprobes simulate_jalr(u32 opcode, unsigned long addr, struct pt_regs *reg

return ret;
}
+
+#define auipc_rd_idx(opcode) \
+ ((opcode >> 7) & 0x1f)
+
+#define auipc_imm(opcode) \
+ ((((opcode) >> 12) & 0xfffff) << 12)
+
+#if __riscv_xlen == 64
+#define auipc_offset(opcode) sign_extend64(auipc_imm(opcode), 31)
+#elif __riscv_xlen == 32
+#define auipc_offset(opcode) auipc_imm(opcode)
+#else
+#error "Unexpected __riscv_xlen"
+#endif
+
+bool __kprobes simulate_auipc(u32 opcode, unsigned long addr, struct pt_regs *regs)
+{
+ /*
+ * auipc instruction:
+ * 31 12 11 7 6 0
+ * | imm[31:12] | rd | opcode |
+ * 20 5 7
+ */
+
+ u32 rd_idx = auipc_rd_idx(opcode);
+ unsigned long rd_val = addr + auipc_offset(opcode);
+
+ if (!rv_insn_reg_set_val(regs, rd_idx, rd_val))
+ return false;
+
+ instruction_pointer_set(regs, addr + 4);
+
+ return true;
+}
--
2.32.0
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