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	__ASSEMBLER__
 18
 19static inline void arch_kgdb_breakpoint(void)
 20{
 21	asm ("brk %0" : : "I" (KGDB_COMPILED_DBG_BRK_IMM));
 22}
 23
 24extern void kgdb_handle_bus_error(void);
 25extern int kgdb_fault_expected;
 26
 27int kgdb_brk_handler(struct pt_regs *regs, unsigned long esr);
 28int kgdb_compiled_brk_handler(struct pt_regs *regs, unsigned long esr);
 29#ifdef CONFIG_KGDB
 30int kgdb_single_step_handler(struct pt_regs *regs, unsigned long esr);
 31#else
 32static inline int kgdb_single_step_handler(struct pt_regs *regs,
 33	unsigned long esr)
 34{
 35	return DBG_HOOK_ERROR;
 36}
 37#endif
 38
 39#endif /* !__ASSEMBLER__ */
 40
 41/*
 42 * gdb remote procotol (well most versions of it) expects the following
 43 * register layout.
 44 *
 45 * General purpose regs:
 46 *     r0-r30: 64 bit
 47 *     sp,pc : 64 bit
 48 *     pstate  : 32 bit
 49 *     Total: 33 + 1
 50 * FPU regs:
 51 *     f0-f31: 128 bit
 52 *     fpsr & fpcr: 32 bit
 53 *     Total: 32 + 2
 54 *
 55 * To expand a little on the "most versions of it"... when the gdb remote
 56 * protocol for AArch64 was developed it depended on a statement in the
 57 * Architecture Reference Manual that claimed "SPSR_ELx is a 32-bit register".
 58 * and, as a result, allocated only 32-bits for the PSTATE in the remote
 59 * protocol. In fact this statement is still present in ARM DDI 0487A.i.
 60 *
 61 * Unfortunately "is a 32-bit register" has a very special meaning for
 62 * system registers. It means that "the upper bits, bits[63:32], are
 63 * RES0.". RES0 is heavily used in the ARM architecture documents as a
 64 * way to leave space for future architecture changes. So to translate a
 65 * little for people who don't spend their spare time reading ARM architecture
 66 * manuals, what "is a 32-bit register" actually means in this context is
 67 * "is a 64-bit register but one with no meaning allocated to any of the
 68 * upper 32-bits... *yet*".
 69 *
 70 * Perhaps then we should not be surprised that this has led to some
 71 * confusion. Specifically a patch, influenced by the above translation,
 72 * that extended PSTATE to 64-bit was accepted into gdb-7.7 but the patch
 73 * was reverted in gdb-7.8.1 and all later releases, when this was
 74 * discovered to be an undocumented protocol change.
 75 *
 76 * So... it is *not* wrong for us to only allocate 32-bits to PSTATE
 77 * here even though the kernel itself allocates 64-bits for the same
 78 * state. That is because this bit of code tells the kernel how the gdb
 79 * remote protocol (well most versions of it) describes the register state.
 80 *
 81 * Note that if you are using one of the versions of gdb that supports
 82 * the gdb-7.7 version of the protocol you cannot use kgdb directly
 83 * without providing a custom register description (gdb can load new
 84 * protocol descriptions at runtime).
 85 */
 86
 87#define _GP_REGS		33
 88#define _FP_REGS		32
 89#define _EXTRA_REGS		3
 90/*
 91 * general purpose registers size in bytes.
 92 * pstate is only 4 bytes. subtract 4 bytes
 93 */
 94#define GP_REG_BYTES		(_GP_REGS * 8)
 95#define DBG_MAX_REG_NUM		(_GP_REGS + _FP_REGS + _EXTRA_REGS)
 96
 97/*
 98 * Size of I/O buffer for gdb packet.
 99 * considering to hold all register contents, size is set
100 */
101
102#define BUFMAX			2048
103
104/*
105 * Number of bytes required for gdb_regs buffer.
106 * _GP_REGS: 8 bytes, _FP_REGS: 16 bytes and _EXTRA_REGS: 4 bytes each
107 * GDB fails to connect for size beyond this with error
108 * "'g' packet reply is too long"
109 */
110
111#define NUMREGBYTES	((_GP_REGS * 8) + (_FP_REGS * 16) + \
112			(_EXTRA_REGS * 4))
113
114#endif /* __ASM_KGDB_H */