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[PATCH] MIPS: microMIPS: Refactor mips16 get_frame_info support

To: ralf@linux-mips.org, Steven.Hill@imgtec.com, linux-mips@linux-mips.org
Subject: [PATCH] MIPS: microMIPS: Refactor mips16 get_frame_info support
From: Tony Wu <tung7970@gmail.com>
Date: Fri, 24 May 2013 22:55:35 +0800
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Current get_frame_info implementation works on word boundary, this
can lead to alignment and endian issues in microMIPS/MIPS16 mode,
due to:

1. MIPS16 instructions can be 16bit or 32bit
2. MIPS16 32bit instructions may not be on the word boundary
3. MIPS16 instructions are placed in 32-bit memory element, in
   endian-dependent order.

Example:
    insn1 = 16bit => word1, hword[0]
    insn2 = 32bit => word1, hword[1], word2, hword[0]
    insn3 = 16bit => word2, hword[1]

       Big Endian
            hword[0]     hword[1]      hword[0]     hword[1]
       +-------------+-------------+-------------+-------------+
       |    insn1    |    insn2    |    insn2'   |    insn3    |
       +-------------+-------------+-------------+-------------+
       31          word1          0 31         word2           0

       Little Endian
            hword[1]     hword[0]      hword[1]     hword[0]
       +-------------+-------------+-------------+-------------+
       |    insn2    |    insn1    |    insn3    |    insn2'   |
       +-------------+-------------+-------------+-------------+
       31          word1          0 31         word2           0

This patch refactors microMIPS get_frame_info by implementing
fetch_instruction() to fetch instructions on word boundary, and
MIPS16_fetch_halfword() to assemble halfwords into 16bit/32bit MIPS16
instructions for further processing.

This patch also fixes sibling call handling and schedule_mfi
initialization for microMIPS.

Signed-off-by: Tony Wu <tung7970@gmail.com>
Cc: Steven J. Hill <Steven.Hill@imgtec.com>
---
 arch/mips/kernel/process.c |  214 +++++++++++++++++++++++++++++---------------
 1 file changed, 141 insertions(+), 73 deletions(-)

diff --git a/arch/mips/kernel/process.c b/arch/mips/kernel/process.c
index c6a041d..c335a7f 100644
--- a/arch/mips/kernel/process.c
+++ b/arch/mips/kernel/process.c
@@ -211,14 +211,17 @@ struct mips_frame_info {
        int             pc_offset;
 };
 
+#ifdef CONFIG_CPU_MICROMIPS
+#define J_TARGET(pc,target)    \
+               (((unsigned long)(pc) & 0xf8000000) | ((target) << 1))
+#else
 #define J_TARGET(pc,target)    \
                (((unsigned long)(pc) & 0xf0000000) | ((target) << 2))
+#endif
 
 static inline int is_ra_save_ins(union mips_instruction *ip)
 {
 #ifdef CONFIG_CPU_MICROMIPS
-       union mips_instruction mmi;
-
        /*
         * swsp ra,offset
         * swm16 reglist,offset(sp)
@@ -228,24 +231,17 @@ static inline int is_ra_save_ins(union mips_instruction 
*ip)
         *
         * microMIPS is way more fun...
         */
-       if (mm_insn_16bit(ip->halfword[0])) {
-               mmi.word = (ip->halfword[0] << 16);
-               return ((mmi.mm16_r5_format.opcode == mm_swsp16_op &&
-                        mmi.mm16_r5_format.rt == 31) ||
-                       (mmi.mm16_m_format.opcode == mm_pool16c_op &&
-                        mmi.mm16_m_format.func == mm_swm16_op));
-       }
-       else {
-               mmi.halfword[0] = ip->halfword[1];
-               mmi.halfword[1] = ip->halfword[0];
-               return ((mmi.mm_m_format.opcode == mm_pool32b_op &&
-                        mmi.mm_m_format.rd > 9 &&
-                        mmi.mm_m_format.base == 29 &&
-                        mmi.mm_m_format.func == mm_swm32_func) ||
-                       (mmi.i_format.opcode == mm_sw32_op &&
-                        mmi.i_format.rs == 29 &&
-                        mmi.i_format.rt == 31));
-       }
+       return ((ip->mm16_r5_format.opcode == mm_swsp16_op &&
+                ip->mm16_r5_format.rt == 31) ||
+               (ip->mm16_m_format.opcode == mm_pool16c_op &&
+                ip->mm16_m_format.func == mm_swm16_op) ||
+               /* 32bit instruction */
+               (ip->mm_m_format.opcode == mm_pool32b_op &&
+                ip->mm_m_format.rd > 9 &&
+                ip->mm_m_format.base == 29 &&
+                ip->mm_m_format.func == mm_swm32_func) ||
+               (ip->i_format.opcode == mm_sw32_op &&
+                ip->i_format.rs == 29 && ip->i_format.rt == 31));
 #else
        /* sw / sd $ra, offset($sp) */
        return (ip->i_format.opcode == sw_op || ip->i_format.opcode == sd_op) &&
@@ -265,16 +261,16 @@ static inline int is_jump_ins(union mips_instruction *ip)
         *
         * microMIPS is kind of more fun...
         */
-       union mips_instruction mmi;
-
-       mmi.word = (ip->halfword[0] << 16);
+       if ((ip->mm16_r5_format.opcode == mm_pool16c_op &&
+           (ip->mm16_r5_format.rt & mm_jr16_op) == mm_jr16_op))
+               return 1;
 
-       if ((mmi.mm16_r5_format.opcode == mm_pool16c_op &&
-           (mmi.mm16_r5_format.rt & mm_jr16_op) == mm_jr16_op) ||
-           ip->j_format.opcode == mm_jal32_op)
+       if (ip->j_format.opcode == mm_jal32_op ||
+           ip->j_format.opcode == mm_j32_op)
                return 1;
+
        if (ip->r_format.opcode != mm_pool32a_op ||
-                       ip->r_format.func != mm_pool32axf_op)
+           ip->r_format.func != mm_pool32axf_op)
                return 0;
        return (((ip->u_format.uimmediate >> 6) & mm_jalr_op) == mm_jalr_op);
 #else
@@ -299,17 +295,13 @@ static inline int is_sp_move_ins(union mips_instruction 
*ip)
         *
         * microMIPS is not more fun...
         */
-       if (mm_insn_16bit(ip->halfword[0])) {
-               union mips_instruction mmi;
-
-               mmi.word = (ip->halfword[0] << 16);
-               return ((mmi.mm16_r3_format.opcode == mm_pool16d_op &&
-                        mmi.mm16_r3_format.simmediate && mm_addiusp_func) ||
-                       (mmi.mm16_r5_format.opcode == mm_pool16d_op &&
-                        mmi.mm16_r5_format.rt == 29));
-       }
-       return (ip->mm_i_format.opcode == mm_addiu32_op &&
-                ip->mm_i_format.rt == 29 && ip->mm_i_format.rs == 29);
+       return ((ip->mm16_r3_format.opcode == mm_pool16d_op &&
+                ip->mm16_r3_format.simmediate && mm_addiusp_func) ||
+               (ip->mm16_r5_format.opcode == mm_pool16d_op &&
+                ip->mm16_r5_format.rt == 29) ||
+               /* 32bit instruction */
+               (ip->mm_i_format.opcode == mm_addiu32_op &&
+                ip->mm_i_format.rt == 29 && ip->mm_i_format.rs == 29));
 #else
        /* addiu/daddiu sp,sp,-imm */
        if (ip->i_format.rs != 29 || ip->i_format.rt != 29)
@@ -320,15 +312,76 @@ static inline int is_sp_move_ins(union mips_instruction 
*ip)
        return 0;
 }
 
-static int get_frame_info(struct mips_frame_info *info)
-{
 #ifdef CONFIG_CPU_MICROMIPS
-       union mips_instruction *ip = (void *) (((char *) info->func) - 1);
+/*
+ * A few fun facts on MIPS16
+ *
+ * 1. MIPS16 instructions are either 16-bit or 32-bit in length
+ * 2. MIPS16 32-bit instruction may not be on word boundary
+ * 3. MIPS16 instructions are placed in 32-bit memory element,
+ *    in endian-dependent order.
+ *
+ *    Big Endian
+ *    +---------------+---------------+
+ *    |      ip1      |      ip2      |
+ *    +---------------+---------------+
+ *
+ *    Little Endian
+ *    +---------------+---------------+
+ *    |      ip2      |      ip1      |
+ *    +---------------+---------------+
+ *
+ * fetch_instruction and MIPS16_fetch_halfword do the followings:
+ *
+ * 1. fetch word from word-aligned address
+ * 2. access the fetched word using halfword (defeat endian issue)
+ * 3. assemble 16/32 bit MIPS16 instruction from halfword(s)
+ */
+static inline void MIPS16_fetch_halfword(union mips_instruction **ip,
+                                        unsigned short *this_halfword,
+                                        unsigned short *prev_halfword)
+{
+       if (*prev_halfword) {
+               *this_halfword = *prev_halfword;
+               *prev_halfword = 0;
+       } else {
+               /* advance pointer to next word */
+               *this_halfword = (*ip)->halfword[0];
+               *prev_halfword = (*ip)->halfword[1];
+               *ip += 1;
+       }
+}
+
+static inline void fetch_instruction(union mips_instruction **ip,
+                                    union mips_instruction *mi,
+                                    unsigned short *prev_halfword)
+{
+       /* fetch the first MIPS16 instruction */
+       MIPS16_fetch_halfword(ip, &mi->halfword[0], prev_halfword);
+
+       /* fetch the second half if it is a 32bit one */
+       if (mm_insn_16bit(mi->halfword[0]))
+               mi->halfword[1] = 0;
+       else
+               MIPS16_fetch_halfword(ip, &mi->halfword[1], prev_halfword);
+}
 #else
-       union mips_instruction *ip = info->func;
+static inline void fetch_instruction(union mips_instruction **ip,
+                                    union mips_instruction *mi,
+                                    unsigned short *halfword)
+{
+       /* do simple assignment for mips32 mode */
+       *mi = **ip;
+       *ip += 1;
+}
 #endif
+
+static int get_frame_info(struct mips_frame_info *info)
+{
+       union mips_instruction *ip = info->func;
+       union mips_instruction inst, *max_ip;
        unsigned max_insns = info->func_size / sizeof(union mips_instruction);
-       unsigned i;
+       unsigned short halfword = 0;
 
        info->pc_offset = -1;
        info->frame_size = 0;
@@ -340,37 +393,38 @@ static int get_frame_info(struct mips_frame_info *info)
                max_insns = 128U;       /* unknown function size */
        max_insns = min(128U, max_insns);
 
-       for (i = 0; i < max_insns; i++, ip++) {
+#ifdef CONFIG_CPU_MICROMIPS
+       /* align start address to word boundary, lose mode bit. */
+       ip = (union mips_instruction *)((unsigned long)ip & ~0x3);
+#endif
+       max_ip = ip + max_insns * sizeof(union mips_instruction);
+
+       while (ip < max_ip) {
+               fetch_instruction(&ip, &inst, &halfword);
 
-               if (is_jump_ins(ip))
+               if (is_jump_ins(&inst))
                        break;
                if (!info->frame_size) {
-                       if (is_sp_move_ins(ip))
-                       {
+                       if (!is_sp_move_ins(&inst))
+                               continue;
 #ifdef CONFIG_CPU_MICROMIPS
-                               if (mm_insn_16bit(ip->halfword[0]))
-                               {
-                                       unsigned short tmp;
-
-                                       if (ip->halfword[0] & mm_addiusp_func)
-                                       {
-                                               tmp = (((ip->halfword[0] >> 1) 
& 0x1ff) << 2);
-                                               info->frame_size = -(signed 
short)(tmp | ((tmp & 0x100) ? 0xfe00 : 0));
-                                       } else {
-                                               tmp = (ip->halfword[0] >> 1);
-                                               info->frame_size = -(signed 
short)(tmp & 0xf);
-                                       }
-                                       ip = (void *) &ip->halfword[1];
-                                       ip--;
-                               } else
+                       if (mm_insn_16bit(inst.halfword[0])) {
+                               unsigned short tmp;
+
+                               if (inst.halfword[0] & mm_addiusp_func) {
+                                       tmp = (((inst.halfword[0] >> 1) & 
0x1ff) << 2);
+                                       info->frame_size = -(signed short)(tmp 
| ((tmp & 0x100) ? 0xfe00 : 0));
+                               } else {
+                                       tmp = (inst.halfword[0] >> 1);
+                                       info->frame_size = -(signed short)(tmp 
& 0xf);
+                               }
+                       } else
 #endif
-                               info->frame_size = - ip->i_format.simmediate;
-                       }
-                       continue;
+                               info->frame_size = - inst.i_format.simmediate;
                }
-               if (info->pc_offset == -1 && is_ra_save_ins(ip)) {
+               if (info->pc_offset == -1 && is_ra_save_ins(&inst)) {
                        info->pc_offset =
-                               ip->i_format.simmediate / sizeof(long);
+                               inst.i_format.simmediate / sizeof(long);
                        break;
                }
        }
@@ -390,20 +444,34 @@ static unsigned long get___schedule_addr(void)
 {
        return kallsyms_lookup_name("__schedule");
 }
-#else
+#else /* CONFIG_KALLSYMS */
 static unsigned long get___schedule_addr(void)
 {
        union mips_instruction *ip = (void *)schedule;
+       union mips_instruction inst;
+       union mips_instruction *max_ip;
        int max_insns = 8;
-       int i;
+       unsigned short halfword;
+
+#ifdef CONFIG_CPU_MICROMIPS
+       /* align start address to word boundary, lose mode bit */
+       ip = (union mips_instruction *)((unsigned long)ip & ~0x3);
+#endif
+       max_ip = ip + max_insns * sizeof(union mips_instruction);
 
-       for (i = 0; i < max_insns; i++, ip++) {
-               if (ip->j_format.opcode == j_op)
-                       return J_TARGET(ip, ip->j_format.target);
+       while (ip < max_ip) {
+               fetch_instruction(&ip, &inst, &halfword);
+#ifdef CONFIG_CPU_MICROMIPS
+               if (inst.j_format.opcode == mm_j32_op)
+                       return J_TARGET(ip+1, inst.j_format.target);
+#else
+               if (inst.j_format.opcode == j_op)
+                       return J_TARGET(ip, inst.j_format.target);
+#endif
        }
        return 0;
 }
-#endif
+#endif /* !CONFIG_KALLSYMS */
 
 static int __init frame_info_init(void)
 {
-- 
1.7.10.2 (Apple Git-33)


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