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 
arch_kgdb_breakpoint(void)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 */
103