MIPS: Fix sibling call handling in get_frame_info

Given a function, get_frame_info() analyzes its instructions
to figure out frame size and return address. get_frame_info()
works as follows:

1. analyze up to 128 instructions if the function size is unknown
2. search for 'addiu/daddiu sp,sp,-immed' for frame size
3. search for 'sw ra,offset(sp)' for return address
4. end search when it sees jr/jal/jalr

This leads to an issue when the given function is a sibling
call, example shown as follows.

801ca110 <schedule>:
801ca110:       8f820000        lw      v0,0(gp)
801ca114:       8c420000        lw      v0,0(v0)
801ca118:       080726f0        j       801c9bc0 <__schedule>
801ca11c:       00000000        nop

801ca120 <io_schedule>:
801ca120:       27bdffe8        addiu   sp,sp,-24
801ca124:       3c028022        lui     v0,0x8022
801ca128:       afbf0014        sw      ra,20(sp)

In this case, get_frame_info() cannot properly detect schedule's
frame info, and eventually returns io_schedule's instead.

This patch adds 'j' to the end search condition to workaround
sibling call cases.
Signed-off-by: Tony Wu <tung7970@gmail.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/5236/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/kernel/process.c

@@ -264,7 +264,7 @@ static inline int is_ra_save_ins(union mips_instruction *ip)
 #endif
 }
 
-static inline int is_jal_jalr_jr_ins(union mips_instruction *ip)
+static inline int is_jump_ins(union mips_instruction *ip)
 {
 #ifdef CONFIG_CPU_MICROMIPS
 	/*
@@ -288,6 +288,8 @@ static inline int is_jal_jalr_jr_ins(union mips_instruction *ip)
 		return 0;
 	return (((ip->u_format.uimmediate >> 6) & mm_jalr_op) == mm_jalr_op);
 #else
+	if (ip->j_format.opcode == j_op)
+		return 1;
 	if (ip->j_format.opcode == jal_op)
 		return 1;
 	if (ip->r_format.opcode != spec_op)
@@ -350,7 +352,7 @@ static int get_frame_info(struct mips_frame_info *info)
 
 	for (i = 0; i < max_insns; i++, ip++) {
 
-		if (is_jal_jalr_jr_ins(ip))
+		if (is_jump_ins(ip))
 			break;
 		if (!info->frame_size) {
 			if (is_sp_move_ins(ip))