linux-kernel - [PATCH 4/4] MIPS: Add is_jr_ra

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Date:   Tue, 12 Jan 2021 20:29:17 +0800
From:   Jinyang He <hejinyang@...ngson.cn>
To:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>
Cc:     linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org,
        Paul Burton <paulburton@...nel.org>,
        Jun-Ru Chang <jrjang@...ltek.com>
Subject: [PATCH 4/4] MIPS: Add is_jr_ra_ins() to end the loop early

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 <hejinyang@...ngson.cn>
---
 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
+	if (ip->r_format.opcode == spec_op &&
+	    ip->r_format.func == jr_op &&
+	    ip->r_format.rs == 31)
+		return 1;
+	return 0;
+#endif
+}
+
 static inline int is_ra_save_ins(union mips_instruction *ip, int *poff)
 {
 #ifdef CONFIG_CPU_MICROMIPS
@@ -417,7 +447,9 @@ static int get_frame_info(struct mips_frame_info *info)
 			last_insn_size = 4;
 		}
 
-		if (!info->frame_size) {
+		if (is_jr_ra_ins(ip)) {
+			break;
+		} else if (!info->frame_size) {
 			is_sp_move_ins(&insn, &info->frame_size);
 			continue;
 		} else if (!saw_jump && is_jump_ins(ip)) {
-- 
2.1.0