arch/arm64/include/asm/kgdb.h

   1 /*
   2  * AArch64 KGDB support
   3  *
   4  * Based on arch/arm/include/kgdb.h
   5  *
   6  * Copyright (C) 2013 Cavium Inc.
   7  * Author: Vijaya Kumar K <vijaya.kumar@caviumnetworks.com>
   8  *
   9  * This program is free software; you can redistribute it and/or modify
  10  * it under the terms of the GNU General Public License version 2 as
  11  * published by the Free Software Foundation.
  12  *
  13  * This program is distributed in the hope that it will be useful,
  14  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  15  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16  * GNU General Public License for more details.
  17  *
  18  * You should have received a copy of the GNU General Public License
  19  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  20  */
  21
  22 #ifndef __ARM_KGDB_H
  23 #define __ARM_KGDB_H
  24
  25 #include <linux/ptrace.h>
  26 #include <asm/debug-monitors.h>
  27
  28 #ifndef __ASSEMBLY__
  29
  30 static inline void arch_kgdb_breakpoint(void)
  31 {
  32         asm ("brk %0" : : "I" (KGDB_COMPILED_DBG_BRK_IMM));
  33 }
  34
  35 extern void kgdb_handle_bus_error(void);
  36 extern int kgdb_fault_expected;
  37
  38 #endif /* !__ASSEMBLY__ */
  39
  40 /*
  41  * gdb remote procotol (well most versions of it) expects the following
  42  * register layout.
  43  *
  44  * General purpose regs:
  45  *     r0-r30: 64 bit
  46  *     sp,pc : 64 bit
  47  *     pstate  : 32 bit
  48  *     Total: 33 + 1
  49  * FPU regs:
  50  *     f0-f31: 128 bit
  51  *     fpsr & fpcr: 32 bit
  52  *     Total: 32 + 2
  53  *
  54  * To expand a little on the "most versions of it"... when the gdb remote
  55  * protocol for AArch64 was developed it depended on a statement in the
  56  * Architecture Reference Manual that claimed "SPSR_ELx is a 32-bit register".
  57  * and, as a result, allocated only 32-bits for the PSTATE in the remote
  58  * protocol. In fact this statement is still present in ARM DDI 0487A.i.
  59  *
  60  * Unfortunately "is a 32-bit register" has a very special meaning for
  61  * system registers. It means that "the upper bits, bits[63:32], are
  62  * RES0.". RES0 is heavily used in the ARM architecture documents as a
  63  * way to leave space for future architecture changes. So to translate a
  64  * little for people who don't spend their spare time reading ARM architecture
  65  * manuals, what "is a 32-bit register" actually means in this context is
  66  * "is a 64-bit register but one with no meaning allocated to any of the
  67  * upper 32-bits... *yet*".
  68  *
  69  * Perhaps then we should not be surprised that this has led to some
  70  * confusion. Specifically a patch, influenced by the above translation,
  71  * that extended PSTATE to 64-bit was accepted into gdb-7.7 but the patch
  72  * was reverted in gdb-7.8.1 and all later releases, when this was
  73  * discovered to be an undocumented protocol change.
  74  *
  75  * So... it is *not* wrong for us to only allocate 32-bits to PSTATE
  76  * here even though the kernel itself allocates 64-bits for the same
  77  * state. That is because this bit of code tells the kernel how the gdb
  78  * remote protocol (well most versions of it) describes the register state.
  79  *
  80  * Note that if you are using one of the versions of gdb that supports
  81  * the gdb-7.7 version of the protocol you cannot use kgdb directly
  82  * without providing a custom register description (gdb can load new
  83  * protocol descriptions at runtime).
  84  */
  85
  86 #define _GP_REGS                33
  87 #define _FP_REGS                32
  88 #define _EXTRA_REGS             3
  89 /*
  90  * general purpose registers size in bytes.
  91  * pstate is only 4 bytes. subtract 4 bytes
  92  */
  93 #define GP_REG_BYTES            (_GP_REGS * 8)
  94 #define DBG_MAX_REG_NUM         (_GP_REGS + _FP_REGS + _EXTRA_REGS)
  95
  96 /*
  97  * Size of I/O buffer for gdb packet.
  98  * considering to hold all register contents, size is set
  99  */
 100
 101 #define BUFMAX                  2048
 102
 103 /*
 104  * Number of bytes required for gdb_regs buffer.
 105  * _GP_REGS: 8 bytes, _FP_REGS: 16 bytes and _EXTRA_REGS: 4 bytes each
 106  * GDB fails to connect for size beyond this with error
 107  * "'g' packet reply is too long"
 108  */
 109
 110 #define NUMREGBYTES     ((_GP_REGS * 8) + (_FP_REGS * 16) + \
 111                         (_EXTRA_REGS * 4))
 112
 113 #endif /* __ASM_KGDB_H */