Root/Documentation/powerpc/ptrace.txt

1GDB intends to support the following hardware debug features of BookE
2processors:
3
44 hardware breakpoints (IAC)
52 hardware watchpoints (read, write and read-write) (DAC)
62 value conditions for the hardware watchpoints (DVC)
7
8For that, we need to extend ptrace so that GDB can query and set these
9resources. Since we're extending, we're trying to create an interface
10that's extendable and that covers both BookE and server processors, so
11that GDB doesn't need to special-case each of them. We added the
12following 3 new ptrace requests.
13
141. PTRACE_PPC_GETHWDEBUGINFO
15
16Query for GDB to discover the hardware debug features. The main info to
17be returned here is the minimum alignment for the hardware watchpoints.
18BookE processors don't have restrictions here, but server processors have
19an 8-byte alignment restriction for hardware watchpoints. We'd like to avoid
20adding special cases to GDB based on what it sees in AUXV.
21
22Since we're at it, we added other useful info that the kernel can return to
23GDB: this query will return the number of hardware breakpoints, hardware
24watchpoints and whether it supports a range of addresses and a condition.
25The query will fill the following structure provided by the requesting process:
26
27struct ppc_debug_info {
28       unit32_t version;
29       unit32_t num_instruction_bps;
30       unit32_t num_data_bps;
31       unit32_t num_condition_regs;
32       unit32_t data_bp_alignment;
33       unit32_t sizeof_condition; /* size of the DVC register */
34       uint64_t features; /* bitmask of the individual flags */
35};
36
37features will have bits indicating whether there is support for:
38
39#define PPC_DEBUG_FEATURE_INSN_BP_RANGE 0x1
40#define PPC_DEBUG_FEATURE_INSN_BP_MASK 0x2
41#define PPC_DEBUG_FEATURE_DATA_BP_RANGE 0x4
42#define PPC_DEBUG_FEATURE_DATA_BP_MASK 0x8
43
442. PTRACE_SETHWDEBUG
45
46Sets a hardware breakpoint or watchpoint, according to the provided structure:
47
48struct ppc_hw_breakpoint {
49        uint32_t version;
50#define PPC_BREAKPOINT_TRIGGER_EXECUTE 0x1
51#define PPC_BREAKPOINT_TRIGGER_READ 0x2
52#define PPC_BREAKPOINT_TRIGGER_WRITE 0x4
53        uint32_t trigger_type; /* only some combinations allowed */
54#define PPC_BREAKPOINT_MODE_EXACT 0x0
55#define PPC_BREAKPOINT_MODE_RANGE_INCLUSIVE 0x1
56#define PPC_BREAKPOINT_MODE_RANGE_EXCLUSIVE 0x2
57#define PPC_BREAKPOINT_MODE_MASK 0x3
58        uint32_t addr_mode; /* address match mode */
59
60#define PPC_BREAKPOINT_CONDITION_MODE 0x3
61#define PPC_BREAKPOINT_CONDITION_NONE 0x0
62#define PPC_BREAKPOINT_CONDITION_AND 0x1
63#define PPC_BREAKPOINT_CONDITION_EXACT 0x1 /* different name for the same thing as above */
64#define PPC_BREAKPOINT_CONDITION_OR 0x2
65#define PPC_BREAKPOINT_CONDITION_AND_OR 0x3
66#define PPC_BREAKPOINT_CONDITION_BE_ALL 0x00ff0000 /* byte enable bits */
67#define PPC_BREAKPOINT_CONDITION_BE(n) (1<<((n)+16))
68        uint32_t condition_mode; /* break/watchpoint condition flags */
69
70        uint64_t addr;
71        uint64_t addr2;
72        uint64_t condition_value;
73};
74
75A request specifies one event, not necessarily just one register to be set.
76For instance, if the request is for a watchpoint with a condition, both the
77DAC and DVC registers will be set in the same request.
78
79With this GDB can ask for all kinds of hardware breakpoints and watchpoints
80that the BookE supports. COMEFROM breakpoints available in server processors
81are not contemplated, but that is out of the scope of this work.
82
83ptrace will return an integer (handle) uniquely identifying the breakpoint or
84watchpoint just created. This integer will be used in the PTRACE_DELHWDEBUG
85request to ask for its removal. Return -ENOSPC if the requested breakpoint
86can't be allocated on the registers.
87
88Some examples of using the structure to:
89
90- set a breakpoint in the first breakpoint register
91
92  p.version = PPC_DEBUG_CURRENT_VERSION;
93  p.trigger_type = PPC_BREAKPOINT_TRIGGER_EXECUTE;
94  p.addr_mode = PPC_BREAKPOINT_MODE_EXACT;
95  p.condition_mode = PPC_BREAKPOINT_CONDITION_NONE;
96  p.addr = (uint64_t) address;
97  p.addr2 = 0;
98  p.condition_value = 0;
99
100- set a watchpoint which triggers on reads in the second watchpoint register
101
102  p.version = PPC_DEBUG_CURRENT_VERSION;
103  p.trigger_type = PPC_BREAKPOINT_TRIGGER_READ;
104  p.addr_mode = PPC_BREAKPOINT_MODE_EXACT;
105  p.condition_mode = PPC_BREAKPOINT_CONDITION_NONE;
106  p.addr = (uint64_t) address;
107  p.addr2 = 0;
108  p.condition_value = 0;
109
110- set a watchpoint which triggers only with a specific value
111
112  p.version = PPC_DEBUG_CURRENT_VERSION;
113  p.trigger_type = PPC_BREAKPOINT_TRIGGER_READ;
114  p.addr_mode = PPC_BREAKPOINT_MODE_EXACT;
115  p.condition_mode = PPC_BREAKPOINT_CONDITION_AND | PPC_BREAKPOINT_CONDITION_BE_ALL;
116  p.addr = (uint64_t) address;
117  p.addr2 = 0;
118  p.condition_value = (uint64_t) condition;
119
120- set a ranged hardware breakpoint
121
122  p.version = PPC_DEBUG_CURRENT_VERSION;
123  p.trigger_type = PPC_BREAKPOINT_TRIGGER_EXECUTE;
124  p.addr_mode = PPC_BREAKPOINT_MODE_RANGE_INCLUSIVE;
125  p.condition_mode = PPC_BREAKPOINT_CONDITION_NONE;
126  p.addr = (uint64_t) begin_range;
127  p.addr2 = (uint64_t) end_range;
128  p.condition_value = 0;
129
1303. PTRACE_DELHWDEBUG
131
132Takes an integer which identifies an existing breakpoint or watchpoint
133(i.e., the value returned from PTRACE_SETHWDEBUG), and deletes the
134corresponding breakpoint or watchpoint..
135

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