1  // Copyright 2015-2019 Espressif Systems (Shanghai) PTE LTD
 2  //
 3  // Licensed under the Apache License, Version 2.0 (the "License");
 4  // you may not use this file except in compliance with the License.
 5  // You may obtain a copy of the License at
 6  //
 7  //     http://www.apache.org/licenses/LICENSE-2.0
 8  //
 9  // Unless required by applicable law or agreed to in writing, software
10  // distributed under the License is distributed on an "AS IS" BASIS,
11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12  // See the License for the specific language governing permissions and
13  // limitations under the License.
14  
15  #include <xtensa/coreasm.h>
16  #include <xtensa/corebits.h>
17  #include <xtensa/config/system.h>
18  #include <xtensa/hal.h>
19  
20  /*
21   * esp_backtrace_get_start(uint32_t *pc, uint32_t *sp, uint32_t *next_pc)
22   *
23   *     High Addr
24   * ..................
25   * |     i-3 BS     |
26   * |   i-1 locals   | Function B
27   * .................. i-1 SP
28   * |     i-2 BS     |
29   * |    i locals    | Function A (Start of backtrace)
30   * ------------------ i SP
31   * |     i-1 BS     |
32   * |   i+1 locals   | Backtracing function (e.g. esp_backtrace_print())
33   * ------------------ i+1 SP
34   * |      i BS      |
35   * |   i+2 locals   | esp_backtrace_get_start() <- This function
36   * ------------------ i+2 SP
37   * |     i+1 BS     |
38   * |   i+3 locals   | xthal_window_spill()
39   * ------------------ i+3 SP
40   * .................. Low Addr
41   */
42      .section    .iram1, "ax"
43      .align      4
44      .global     esp_backtrace_get_start
45      .type       esp_backtrace_get_start, @function
46  esp_backtrace_get_start:
47      entry   a1, 32
48      call8   xthal_window_spill  //Spill registers onto stack (excluding this function)
49      //a2, a3, a4 should be out arguments for i SP, i PC, i-1 PC respectively. Use a5 and a6 as scratch
50      l32e    a5, sp, -16         //Get i PC, which is ret addres of i+1
51      s32i    a5, a2, 0           //Store i PC to arg *pc
52      l32e    a6, sp, -12         //Get i+1 SP. Used to access i BS
53      l32e    a5, a6, -12         //Get i SP
54      s32i    a5, a3, 0           //Store i SP to arg *sp
55      l32e    a5, a6, -16         //Get i-1 PC, which is ret address of i
56      s32i    a5, a4, 0           //Store i-1 PC to arg *next_pc
57      retw