arch/arm64/include/asm/kgdb.h

   1 /* SPDX-License-Identifier: GPL-2.0-only */
   2 /*
   3  * AArch64 KGDB support
   4  *
   5  * Based on arch/arm/include/kgdb.h
   6  *
   7  * Copyright (C) 2013 Cavium Inc.
   8  * Author: Vijaya Kumar K <vijaya.kumar@caviumnetworks.com>
   9  */
  10
  11 #ifndef __ARM_KGDB_H
  12 #define __ARM_KGDB_H
  13
  14 #include <linux/ptrace.h>
  15 #include <asm/debug-monitors.h>
  16
  17 #ifndef __ASSEMBLY__
  18
  19 static inline void arch_kgdb_breakpoint(void)
  20 {
  21         asm ("brk %0" : : "I" (KGDB_COMPILED_DBG_BRK_IMM));
  22 }
  23
  24 extern void kgdb_handle_bus_error(void);
  25 extern int kgdb_fault_expected;
  26
  27 #endif /* !__ASSEMBLY__ */
  28
  29 /*
  30  * gdb remote procotol (well most versions of it) expects the following
  31  * register layout.
  32  *
  33  * General purpose regs:
  34  *     r0-r30: 64 bit
  35  *     sp,pc : 64 bit
  36  *     pstate  : 32 bit
  37  *     Total: 33 + 1
  38  * FPU regs:
  39  *     f0-f31: 128 bit
  40  *     fpsr & fpcr: 32 bit
  41  *     Total: 32 + 2
  42  *
  43  * To expand a little on the "most versions of it"... when the gdb remote
  44  * protocol for AArch64 was developed it depended on a statement in the
  45  * Architecture Reference Manual that claimed "SPSR_ELx is a 32-bit register".
  46  * and, as a result, allocated only 32-bits for the PSTATE in the remote
  47  * protocol. In fact this statement is still present in ARM DDI 0487A.i.
  48  *
  49  * Unfortunately "is a 32-bit register" has a very special meaning for
  50  * system registers. It means that "the upper bits, bits[63:32], are
  51  * RES0.". RES0 is heavily used in the ARM architecture documents as a
  52  * way to leave space for future architecture changes. So to translate a
  53  * little for people who don't spend their spare time reading ARM architecture
  54  * manuals, what "is a 32-bit register" actually means in this context is
  55  * "is a 64-bit register but one with no meaning allocated to any of the
  56  * upper 32-bits... *yet*".
  57  *
  58  * Perhaps then we should not be surprised that this has led to some
  59  * confusion. Specifically a patch, influenced by the above translation,
  60  * that extended PSTATE to 64-bit was accepted into gdb-7.7 but the patch
  61  * was reverted in gdb-7.8.1 and all later releases, when this was
  62  * discovered to be an undocumented protocol change.
  63  *
  64  * So... it is *not* wrong for us to only allocate 32-bits to PSTATE
  65  * here even though the kernel itself allocates 64-bits for the same
  66  * state. That is because this bit of code tells the kernel how the gdb
  67  * remote protocol (well most versions of it) describes the register state.
  68  *
  69  * Note that if you are using one of the versions of gdb that supports
  70  * the gdb-7.7 version of the protocol you cannot use kgdb directly
  71  * without providing a custom register description (gdb can load new
  72  * protocol descriptions at runtime).
  73  */
  74
  75 #define _GP_REGS                33
  76 #define _FP_REGS                32
  77 #define _EXTRA_REGS             3
  78 /*
  79  * general purpose registers size in bytes.
  80  * pstate is only 4 bytes. subtract 4 bytes
  81  */
  82 #define GP_REG_BYTES            (_GP_REGS * 8)
  83 #define DBG_MAX_REG_NUM         (_GP_REGS + _FP_REGS + _EXTRA_REGS)
  84
  85 /*
  86  * Size of I/O buffer for gdb packet.
  87  * considering to hold all register contents, size is set
  88  */
  89
  90 #define BUFMAX                  2048
  91
  92 /*
  93  * Number of bytes required for gdb_regs buffer.
  94  * _GP_REGS: 8 bytes, _FP_REGS: 16 bytes and _EXTRA_REGS: 4 bytes each
  95  * GDB fails to connect for size beyond this with error
  96  * "'g' packet reply is too long"
  97  */
  98
  99 #define NUMREGBYTES     ((_GP_REGS * 8) + (_FP_REGS * 16) + \
 100                         (_EXTRA_REGS * 4))
 101
 102 #endif /* __ASM_KGDB_H */