1 Ramoops oops/panic logger
2 =========================
3
4 Sergiu Iordache <sergiu@chromium.org>
5
6 Updated: 10 Feb 2021
7
8 Introduction
9 ------------
10
11 Ramoops is an oops/panic logger that writes it
12 crashes. It works by logging oopses and panics
13 needs a system with persistent RAM so that the
14 survive after a restart.
15
16 Ramoops concepts
17 ----------------
18
19 Ramoops uses a predefined memory area to store
20 and type of the memory area are set using thre
21
22 * ``mem_address`` for the start
23 * ``mem_size`` for the size. The memory size
24 power of two.
25 * ``mem_type`` to specify if the memory type
26 * ``mem_name`` to specify a memory region de
27 line parameter.
28
29 Typically the default value of ``mem_type=0``
30 mapping to pgprot_writecombine. Setting ``mem_
31 ``pgprot_noncached``, which only works on some
32 depends on atomic operations. At least on ARM,
33 memory to be mapped strongly ordered, and atom
34 memory are implementation defined, and won't w
35 Setting ``mem_type=2`` attempts to treat the m
36 which enables full cache on it. This can impro
37
38 The memory area is divided into ``record_size`
39 power of two) and each kmesg dump writes a ``r
40 information.
41
42 Limiting which kinds of kmsg dumps are stored
43 the ``max_reason`` value, as defined in includ
44 ``enum kmsg_dump_reason``. For example, to sto
45 ``max_reason`` should be set to 2 (KMSG_DUMP_O
46 ``max_reason`` should be set to 1 (KMSG_DUMP_P
47 (KMSG_DUMP_UNDEF), means the reason filtering
48 ``printk.always_kmsg_dump`` boot param: if uns
49 otherwise KMSG_DUMP_MAX.
50
51 The module uses a counter to record multiple d
52 on restart (i.e. new dumps after the restart w
53
54 Ramoops also supports software ECC protection
55 This might be useful when a hardware reset was
56 to life (i.e. a watchdog triggered). In such c
57 corrupt, but usually it is restorable.
58
59 Setting the parameters
60 ----------------------
61
62 Setting the ramoops parameters can be done in
63
64 A. Use the module parameters (which have the
65 as before). For quick debugging, you can also
66 boot and then use the reserved memory for ram
67 machine with > 128 MB of memory, the followin
68 the kernel to use only the first 128 MB of me
69 ramoops region at 128 MB boundary::
70
71 mem=128M ramoops.mem_address=0x8000000
72
73 B. Use Device Tree bindings, as described in
74 ``Documentation/devicetree/bindings/reserved-
75 For example::
76
77 reserved-memory {
78 #address-cells = <2>;
79 #size-cells = <2>;
80 ranges;
81
82 ramoops@8f000000 {
83 compatible = "ramoops"
84 reg = <0 0x8f000000 0
85 record-size = <0x4000>
86 console-size = <0x4000
87 };
88 };
89
90 C. Use a platform device and set the platform
91 be set through that platform data. An example
92
93 .. code-block:: c
94
95 #include <linux/pstore_ram.h>
96 [...]
97
98 static struct ramoops_platform_data ramoops_
99 .mem_size = <...>,
100 .mem_address = <...>,
101 .mem_type = <...>,
102 .record_size = <...>,
103 .max_reason = <...>,
104 .ecc = <...>,
105 };
106
107 static struct platform_device ramoops_dev =
108 .name = "ramoops",
109 .dev = {
110 .platform_data = &ramoops_data
111 },
112 };
113
114 [... inside a function ...]
115 int ret;
116
117 ret = platform_device_register(&ramoops_dev)
118 if (ret) {
119 printk(KERN_ERR "unable to register pl
120 return ret;
121 }
122
123 D. Using a region of memory reserved via ``re
124 parameter. The address and size will be de
125 parameter. Note, that ``reserve_mem`` may
126 in the same location, and cannot be relied
127 to be done, and it may not work on every m
128 Consider this a "best effort" approach. Th
129 takes a size, alignment and name as argume
130 to map the memory to a label that can be r
131
132 reserve_mem=2M:4096:oops ramoops.mem_
133
134 You can specify either RAM memory or periphera
135 specifying RAM, be sure to reserve the memory
136 very early in the architecture code, e.g.::
137
138 #include <linux/memblock.h>
139
140 memblock_reserve(ramoops_data.mem_addr
141
142 Dump format
143 -----------
144
145 The data dump begins with a header, currently
146 timestamp and a new line. The dump then contin
147
148 Reading the data
149 ----------------
150
151 The dump data can be read from the pstore file
152 files is ``dmesg-ramoops-N``, where N is the r
153 a stored record from RAM, simply unlink the re
154
155 Persistent function tracing
156 ---------------------------
157
158 Persistent function tracing might be useful fo
159 related hangs. The functions call chain log is
160 file. Here is an example of usage::
161
162 # mount -t debugfs debugfs /sys/kernel/debug/
163 # echo 1 > /sys/kernel/debug/pstore/record_ft
164 # reboot -f
165 [...]
166 # mount -t pstore pstore /mnt/
167 # tail /mnt/ftrace-ramoops
168 0 ffffffff8101ea64 ffffffff8101bcda native_
169 0 ffffffff8101ea44 ffffffff8101bcf6 native_
170 0 ffffffff81020084 ffffffff8101a4b5 hpet_di
171 0 ffffffff81005f94 ffffffff8101a4bb iommu_s
172 0 ffffffff8101a6a1 ffffffff8101a437 native_
173 0 ffffffff811f9876 ffffffff8101a73a acpi_re
174 0 ffffffff8101a514 ffffffff8101a772 mach_re
175 0 ffffffff811d9c54 ffffffff8101a7a0 __const
176 0 ffffffff811d9c34 ffffffff811d9c80 __delay
177 0 ffffffff811d9d14 ffffffff811d9c3f delay_t
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