payloads/libpayload/arch/arm/gdb.c

   1 /*
   2  * Copyright 2014 Google Inc.
   3  *
   4  * This program is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU General Public License as
   6  * published by the Free Software Foundation; either version 2 of
   7  * the License, or (at your option) any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful,
  10  * but without any warranty; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  */
  14
  15 #include <exception.h>
  16 #include <gdb.h>
  17 #include <libpayload.h>
  18
  19 struct gdb_regs
  20 {
  21         u32 r[16];
  22         struct fp_reg
  23         {
  24                 u8 byte[12];
  25         } __packed f[8];
  26         u32 fps;
  27         u32 cpsr;
  28 } __packed;
  29
  30 static const u8 type_to_signal[] = {
  31         [EXC_UNDEF]  = GDB_SIGILL,
  32         [EXC_SWI]    = GDB_SIGTRAP,
  33         [EXC_PABORT] = GDB_SIGSEGV,
  34         [EXC_DABORT] = GDB_SIGSEGV,
  35 };
  36
  37 /* Scratch value to write reentrant exception states to. We never read it. */
  38 static struct exception_state sentinel_exception_state;
  39
  40 static int gdb_exception_hook(u32 type)
  41 {
  42         if (!gdb_handle_reentrant_exception()) {
  43                 if (type >= ARRAY_SIZE(type_to_signal) || !type_to_signal[type])
  44                         return 0;
  45                 exception_state_ptr = &sentinel_exception_state;
  46                 gdb_command_loop(type_to_signal[type]);
  47         }
  48
  49         exception_state_ptr = &exception_state;
  50         return 1;
  51 }
  52
  53 void gdb_arch_init(void)
  54 {
  55         exception_install_hook(&gdb_exception_hook);
  56 }
  57
  58 void gdb_arch_enter(void)
  59 {
  60         u32 *sp;
  61
  62         asm volatile ("mov %0, %%sp" : "=r"(sp) );
  63
  64         /* Avoid reentrant exceptions, just call the hook if in one already. */
  65         if (sp >= exception_stack && sp <= exception_stack_end)
  66                 gdb_exception_hook(EXC_SWI);
  67         else
  68                 asm volatile ("svc #0");
  69 }
  70
  71 int gdb_arch_set_single_step(int on)
  72 {
  73         /* GDB seems to only need this on x86, ARM works fine without it. */
  74         return -1;
  75 }
  76
  77 void gdb_arch_encode_regs(struct gdb_message *message)
  78 {
  79         gdb_message_encode_bytes(message, exception_state.regs,
  80                                  sizeof(exception_state.regs));
  81         gdb_message_encode_zero_bytes(message,
  82                 offsetof(struct gdb_regs, cpsr) - offsetof(struct gdb_regs, f));
  83         gdb_message_encode_bytes(message, &exception_state.cpsr,
  84                                  sizeof(exception_state.cpsr));
  85 }
  86
  87 void gdb_arch_decode_regs(int offset, struct gdb_message *message)
  88 {
  89         const int cpsr_hex_offset = offsetof(struct gdb_regs, cpsr) * 2;
  90         gdb_message_decode_bytes(message, offset,
  91                         exception_state.regs, sizeof(exception_state.regs));
  92         gdb_message_decode_bytes(message, offset + cpsr_hex_offset,
  93                         &exception_state.cpsr, sizeof(exception_state.cpsr));
  94 }