On 10/24/2021 02:32 AM, Maciej W. Rozycki wrote:

On Tue, 12 Jan 2021, Jinyang He wrote:

quoted

For those leaf functions, they are likely to have no stack operations.
Add is_jr_ra_ins() to determine whether jr ra has been touched before
the frame_size is found. Without this patch, the get frame_size operation
may be out of range and get the frame_size from the next nested function.

Signed-off-by: Jinyang He <redacted>
---
  arch/mips/kernel/process.c | 34 +++++++++++++++++++++++++++++++++-
  1 file changed, 33 insertions(+), 1 deletion(-)

diff --git a/arch/mips/kernel/process.c b/arch/mips/kernel/process.c
index bef8f8d..9e6f194 100644
--- a/arch/mips/kernel/process.c
+++ b/arch/mips/kernel/process.c

@@ -205,6 +205,36 @@ struct mips_frame_info {
  #define J_TARGET(pc,target)	\
  		(((unsigned long)(pc) & 0xf0000000) | ((target) << 2))
  
+static inline int is_jr_ra_ins(union mips_instruction *ip)
+{
+#ifdef CONFIG_CPU_MICROMIPS
+	/*
+	 * jr16 ra
+	 * jr ra
+	 */
+	if (mm_insn_16bit(ip->word >> 16)) {
+		if (ip->mm16_r5_format.opcode == mm_pool16c_op &&
+		    ip->mm16_r5_format.rt == mm_jr16_op &&
+		    ip->mm16_r5_format.imm == 31)
+			return 1;
+		return 0;
+	}
+
+	if (ip->r_format.opcode == mm_pool32a_op &&
+	    ip->r_format.func == mm_pool32axf_op &&
+	    ((ip->u_format.uimmediate >> 6) & GENMASK(9,0)) == mm_jalr_op &&
+            ip->r_format.rs == 31)
+		return 1;
+	return 0;
+#else

  Without looking into it much, this is likely missing the point, because
while technically inteed JR and JR16 can be used with $ra in microMIPS
machine code (there's JRS too), in reality either JRC or JRADDIUSP will.

  [Wading through e-mail recovered from mid-Jan linux-mips.org crash.]

   Maciej

You are right, I missed the point. I have refered to microMIPS64
Instruction Set. JRC and JRADDIUSP also can be used with $ra in
microMIPS. I am not sure what compiler do at epilogue. But when
we call $ra without saving $ra, it means return, I think.
I will fix it later.

Thanks,
Jinyang.