linux/Documentation/printk-formats.txt
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   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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