releases/4.10.2/mips-calculate-micromips-ra-properly-when-unwinding-the-stack.patch

   1 From bb9bc4689b9c635714fbcd5d335bad9934a7ebfc Mon Sep 17 00:00:00 2001
   2 From: Paul Burton <paul.burton@imgtec.com>
   3 Date: Mon, 7 Nov 2016 15:07:06 +0000
   4 Subject: MIPS: Calculate microMIPS ra properly when unwinding the stack
   5
   6 From: Paul Burton <paul.burton@imgtec.com>
   7
   8 commit bb9bc4689b9c635714fbcd5d335bad9934a7ebfc upstream.
   9
  10 get_frame_info() calculates the offset of the return address within a
  11 stack frame simply by dividing a the bottom 16 bits of the instruction,
  12 treated as a signed integer, by the size of a long. Whilst this works
  13 for MIPS32 & MIPS64 ISAs where the sw or sd instructions are used, it's
  14 incorrect for microMIPS where encodings differ. The result is that we
  15 typically completely fail to unwind the stack on microMIPS.
  16
  17 Fix this by adjusting is_ra_save_ins() to calculate the return address
  18 offset, and take into account the various different encodings there in
  19 the same place as we consider whether an instruction is storing the
  20 ra/$31 register.
  21
  22 With this we are now able to unwind the stack for kernels targetting the
  23 microMIPS ISA, for example we can produce:
  24
  25     Call Trace:
  26     [<80109e1f>] show_stack+0x63/0x7c
  27     [<8011ea17>] __warn+0x9b/0xac
  28     [<8011ea45>] warn_slowpath_fmt+0x1d/0x20
  29     [<8013fe53>] register_console+0x43/0x314
  30     [<8067c58d>] of_setup_earlycon+0x1dd/0x1ec
  31     [<8067f63f>] early_init_dt_scan_chosen_stdout+0xe7/0xf8
  32     [<8066c115>] do_early_param+0x75/0xac
  33     [<801302f9>] parse_args+0x1dd/0x308
  34     [<8066c459>] parse_early_options+0x25/0x28
  35     [<8066c48b>] parse_early_param+0x2f/0x38
  36     [<8066e8cf>] setup_arch+0x113/0x488
  37     [<8066c4f3>] start_kernel+0x57/0x328
  38     ---[ end trace 0000000000000000 ]---
  39
  40 Whereas previously we only produced:
  41
  42     Call Trace:
  43     [<80109e1f>] show_stack+0x63/0x7c
  44     ---[ end trace 0000000000000000 ]---
  45
  46 Signed-off-by: Paul Burton <paul.burton@imgtec.com>
  47 Fixes: 34c2f668d0f6 ("MIPS: microMIPS: Add unaligned access support.")
  48 Cc: Leonid Yegoshin <leonid.yegoshin@imgtec.com>
  49 Cc: linux-mips@linux-mips.org
  50 Patchwork: https://patchwork.linux-mips.org/patch/14532/
  51 Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
  52 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  53
  54 ---
  55  arch/mips/kernel/process.c |   85 +++++++++++++++++++++++++++++++++------------
  56  1 file changed, 64 insertions(+), 21 deletions(-)
  57
  58 --- a/arch/mips/kernel/process.c
  59 +++ b/arch/mips/kernel/process.c
  60 @@ -195,7 +195,7 @@ struct mips_frame_info {
  61  #define J_TARGET(pc,target)    \
  62                 (((unsigned long)(pc) & 0xf0000000) | ((target) << 2))
  63
  64 -static inline int is_ra_save_ins(union mips_instruction *ip)
  65 +static inline int is_ra_save_ins(union mips_instruction *ip, int *poff)
  66  {
  67  #ifdef CONFIG_CPU_MICROMIPS
  68         /*
  69 @@ -208,25 +208,70 @@ static inline int is_ra_save_ins(union m
  70          * microMIPS is way more fun...
  71          */
  72         if (mm_insn_16bit(ip->halfword[1])) {
  73 -               return (ip->mm16_r5_format.opcode == mm_swsp16_op &&
  74 -                       ip->mm16_r5_format.rt == 31) ||
  75 -                      (ip->mm16_m_format.opcode == mm_pool16c_op &&
  76 -                       ip->mm16_m_format.func == mm_swm16_op);
  77 -       }
  78 -       else {
  79 -               return (ip->mm_m_format.opcode == mm_pool32b_op &&
  80 -                       ip->mm_m_format.rd > 9 &&
  81 -                       ip->mm_m_format.base == 29 &&
  82 -                       ip->mm_m_format.func == mm_swm32_func) ||
  83 -                      (ip->i_format.opcode == mm_sw32_op &&
  84 -                       ip->i_format.rs == 29 &&
  85 -                       ip->i_format.rt == 31);
  86 +               switch (ip->mm16_r5_format.opcode) {
  87 +               case mm_swsp16_op:
  88 +                       if (ip->mm16_r5_format.rt != 31)
  89 +                               return 0;
  90 +
  91 +                       *poff = ip->mm16_r5_format.simmediate;
  92 +                       *poff = (*poff << 2) / sizeof(ulong);
  93 +                       return 1;
  94 +
  95 +               case mm_pool16c_op:
  96 +                       switch (ip->mm16_m_format.func) {
  97 +                       case mm_swm16_op:
  98 +                               *poff = ip->mm16_m_format.imm;
  99 +                               *poff += 1 + ip->mm16_m_format.rlist;
 100 +                               *poff = (*poff << 2) / sizeof(ulong);
 101 +                               return 1;
 102 +
 103 +                       default:
 104 +                               return 0;
 105 +                       }
 106 +
 107 +               default:
 108 +                       return 0;
 109 +               }
 110 +       }
 111 +
 112 +       switch (ip->i_format.opcode) {
 113 +       case mm_sw32_op:
 114 +               if (ip->i_format.rs != 29)
 115 +                       return 0;
 116 +               if (ip->i_format.rt != 31)
 117 +                       return 0;
 118 +
 119 +               *poff = ip->i_format.simmediate / sizeof(ulong);
 120 +               return 1;
 121 +
 122 +       case mm_pool32b_op:
 123 +               switch (ip->mm_m_format.func) {
 124 +               case mm_swm32_func:
 125 +                       if (ip->mm_m_format.rd < 0x10)
 126 +                               return 0;
 127 +                       if (ip->mm_m_format.base != 29)
 128 +                               return 0;
 129 +
 130 +                       *poff = ip->mm_m_format.simmediate;
 131 +                       *poff += (ip->mm_m_format.rd & 0xf) * sizeof(u32);
 132 +                       *poff /= sizeof(ulong);
 133 +                       return 1;
 134 +               default:
 135 +                       return 0;
 136 +               }
 137 +
 138 +       default:
 139 +               return 0;
 140         }
 141  #else
 142         /* sw / sd $ra, offset($sp) */
 143 -       return (ip->i_format.opcode == sw_op || ip->i_format.opcode == sd_op) &&
 144 -               ip->i_format.rs == 29 &&
 145 -               ip->i_format.rt == 31;
 146 +       if ((ip->i_format.opcode == sw_op || ip->i_format.opcode == sd_op) &&
 147 +               ip->i_format.rs == 29 && ip->i_format.rt == 31) {
 148 +               *poff = ip->i_format.simmediate / sizeof(ulong);
 149 +               return 1;
 150 +       }
 151 +
 152 +       return 0;
 153  #endif
 154  }
 155
 156 @@ -349,11 +394,9 @@ static int get_frame_info(struct mips_fr
 157                         }
 158                         continue;
 159                 }
 160 -               if (info->pc_offset == -1 && is_ra_save_ins(&insn)) {
 161 -                       info->pc_offset =
 162 -                               ip->i_format.simmediate / sizeof(long);
 163 +               if (info->pc_offset == -1 &&
 164 +                   is_ra_save_ins(&insn, &info->pc_offset))
 165                         break;
 166 -               }
 167         }
 168         if (info->frame_size && info->pc_offset >= 0) /* nested */
 169                 return 0;