Root/Documentation/printk-formats.txt

1If variable is of Type, use printk format specifier:
2---------------------------------------------------------
3        int %d or %x
4        unsigned int %u or %x
5        long %ld or %lx
6        unsigned long %lu or %lx
7        long long %lld or %llx
8        unsigned long long %llu or %llx
9        size_t %zu or %zx
10        ssize_t %zd or %zx
11
12Raw pointer value SHOULD be printed with %p. The kernel supports
13the following extended format specifiers for pointer types:
14
15Symbols/Function Pointers:
16
17    %pF versatile_init+0x0/0x110
18    %pf versatile_init
19    %pS versatile_init+0x0/0x110
20    %ps versatile_init
21    %pB prev_fn_of_versatile_init+0x88/0x88
22
23    For printing symbols and function pointers. The 'S' and 's' specifiers
24    result in the symbol name with ('S') or without ('s') offsets. Where
25    this is used on a kernel without KALLSYMS - the symbol address is
26    printed instead.
27
28    The 'B' specifier results in the symbol name with offsets and should be
29    used when printing stack backtraces. The specifier takes into
30    consideration the effect of compiler optimisations which may occur
31    when tail-call's are used and marked with the noreturn GCC attribute.
32
33    On ia64, ppc64 and parisc64 architectures function pointers are
34    actually function descriptors which must first be resolved. The 'F' and
35    'f' specifiers perform this resolution and then provide the same
36    functionality as the 'S' and 's' specifiers.
37
38Kernel Pointers:
39
40    %pK 0x01234567 or 0x0123456789abcdef
41
42    For printing kernel pointers which should be hidden from unprivileged
43    users. The behaviour of %pK depends on the kptr_restrict sysctl - see
44    Documentation/sysctl/kernel.txt for more details.
45
46Struct Resources:
47
48    %pr [mem 0x60000000-0x6fffffff flags 0x2200] or
49        [mem 0x0000000060000000-0x000000006fffffff flags 0x2200]
50    %pR [mem 0x60000000-0x6fffffff pref] or
51        [mem 0x0000000060000000-0x000000006fffffff pref]
52
53    For printing struct resources. The 'R' and 'r' specifiers result in a
54    printed resource with ('R') or without ('r') a decoded flags member.
55
56MAC/FDDI addresses:
57
58    %pM 00:01:02:03:04:05
59    %pMF 00-01-02-03-04-05
60    %pm 000102030405
61
62    For printing 6-byte MAC/FDDI addresses in hex notation. The 'M' and 'm'
63    specifiers result in a printed address with ('M') or without ('m') byte
64    separators. The default byte separator is the colon (':').
65
66    Where FDDI addresses are concerned the 'F' specifier can be used after
67    the 'M' specifier to use dash ('-') separators instead of the default
68    separator.
69
70IPv4 addresses:
71
72    %pI4 1.2.3.4
73    %pi4 001.002.003.004
74    %p[Ii][hnbl]
75
76    For printing IPv4 dot-separated decimal addresses. The 'I4' and 'i4'
77    specifiers result in a printed address with ('i4') or without ('I4')
78    leading zeros.
79
80    The additional 'h', 'n', 'b', and 'l' specifiers are used to specify
81    host, network, big or little endian order addresses respectively. Where
82    no specifier is provided the default network/big endian order is used.
83
84IPv6 addresses:
85
86    %pI6 0001:0002:0003:0004:0005:0006:0007:0008
87    %pi6 00010002000300040005000600070008
88    %pI6c 1:2:3:4:5:6:7:8
89
90    For printing IPv6 network-order 16-bit hex addresses. The 'I6' and 'i6'
91    specifiers result in a printed address with ('I6') or without ('i6')
92    colon-separators. Leading zeros are always used.
93
94    The additional 'c' specifier can be used with the 'I' specifier to
95    print a compressed IPv6 address as described by
96    http://tools.ietf.org/html/rfc5952
97
98UUID/GUID addresses:
99
100    %pUb 00010203-0405-0607-0809-0a0b0c0d0e0f
101    %pUB 00010203-0405-0607-0809-0A0B0C0D0E0F
102    %pUl 03020100-0504-0706-0809-0a0b0c0e0e0f
103    %pUL 03020100-0504-0706-0809-0A0B0C0E0E0F
104
105    For printing 16-byte UUID/GUIDs addresses. The additional 'l', 'L',
106    'b' and 'B' specifiers are used to specify a little endian order in
107    lower ('l') or upper case ('L') hex characters - and big endian order
108    in lower ('b') or upper case ('B') hex characters.
109
110    Where no additional specifiers are used the default little endian
111    order with lower case hex characters will be printed.
112
113struct va_format:
114
115    %pV
116
117    For printing struct va_format structures. These contain a format string
118    and va_list as follows:
119
120    struct va_format {
121        const char *fmt;
122        va_list *va;
123    };
124
125    Do not use this feature without some mechanism to verify the
126    correctness of the format string and va_list arguments.
127
128u64 SHOULD be printed with %llu/%llx, (unsigned long long):
129
130    printk("%llu", (unsigned long long)u64_var);
131
132s64 SHOULD be printed with %lld/%llx, (long long):
133
134    printk("%lld", (long long)s64_var);
135
136If <type> is dependent on a config option for its size (e.g., sector_t,
137blkcnt_t, phys_addr_t, resource_size_t) or is architecture-dependent
138for its size (e.g., tcflag_t), use a format specifier of its largest
139possible type and explicitly cast to it. Example:
140
141    printk("test: sector number/total blocks: %llu/%llu\n",
142        (unsigned long long)sector, (unsigned long long)blockcount);
143
144Reminder: sizeof() result is of type size_t.
145
146Thank you for your cooperation and attention.
147
148
149By Randy Dunlap <rdunlap@xenotime.net> and
150Andrew Murray <amurray@mpc-data.co.uk>
151

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