Thread (14 messages) 14 messages, 5 authors, 2021-10-25

Re: [PATCH 4/4] MIPS: Add is_jr_ra_ins() to end the loop early

From: "Maciej W. Rozycki" <macro@orcam.me.uk>
Date: 2021-10-23 18:32:33
Also in: lkml

On Tue, 12 Jan 2021, Jinyang He wrote:
quoted hunk ↗ jump to hunk
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
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