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[PATCH 1/2] MIPS: detect sibling call in get_frame_info

To: ralf@linux-mips.org, linux-mips@linux-mips.org
Subject: [PATCH 1/2] MIPS: detect sibling call in get_frame_info
From: Tony Wu <tung7970@gmail.com>
Date: Thu, 9 May 2013 22:47:53 +0800
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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 given 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 info instead.

This patch adds sibling call check by detecting out of range jump.

Signed-off-by: Tony Wu <tung7970@gmail.com>
---
 arch/mips/kernel/process.c |   22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/arch/mips/kernel/process.c b/arch/mips/kernel/process.c
index cfc742d..a794eb5 100644
--- a/arch/mips/kernel/process.c
+++ b/arch/mips/kernel/process.c
@@ -223,6 +223,9 @@ struct mips_frame_info {
        int             pc_offset;
 };
 
+#define J_TARGET(pc,target)    \
+               (((unsigned long)(pc) & 0xf0000000) | ((target) << 2))
+
 static inline int is_ra_save_ins(union mips_instruction *ip)
 {
        /* sw / sd $ra, offset($sp) */
@@ -250,11 +253,25 @@ static inline int is_sp_move_ins(union mips_instruction 
*ip)
        return 0;
 }
 
+static inline int is_sibling_j_ins(union mips_instruction *ip,
+                                  unsigned long func_begin, unsigned long 
func_end)
+{
+       if (ip->j_format.opcode == j_op) {
+               unsigned long addr;
+
+               addr = J_TARGET(ip, ip->j_format.target);
+               if (addr < func_begin || addr > func_end)
+                       return 1;
+       }
+       return 0;
+}
+
 static int get_frame_info(struct mips_frame_info *info)
 {
        union mips_instruction *ip = info->func;
        unsigned max_insns = info->func_size / sizeof(union mips_instruction);
        unsigned i;
+       unsigned long func_begin, func_end;
 
        info->pc_offset = -1;
        info->frame_size = 0;
@@ -266,10 +283,15 @@ static int get_frame_info(struct mips_frame_info *info)
                max_insns = 128U;       /* unknown function size */
        max_insns = min(128U, max_insns);
 
+       func_begin = (unsigned long) info->func;
+       func_end = func_begin + max_insns * sizeof(union mips_instruction);
+
        for (i = 0; i < max_insns; i++, ip++) {
 
                if (is_jal_jalr_jr_ins(ip))
                        break;
+               if (is_sibling_j_ins(ip, func_begin, func_end))
+                       break;
                if (!info->frame_size) {
                        if (is_sp_move_ins(ip))
                                info->frame_size = - ip->i_format.simmediate;
-- 
1.7.10.2 (Apple Git-33)

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