123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165166167168169170171172173174175176177178179180181182183184185186187188189190191192193194195196197198199200201202203204205206207208209210211212213214215216217218219220221222223224225226227228229230231232233234235236237238239240241242243244245246247248249250251252253254255256257258259260261262263264265266267268269270271272273274275276277278279280281282283284285286287288289290291292293294295296297298299300301302303304305306307308309310311312313314315316317318319320321322323324325326327328329330331332333334335336337338339340341342343344345346347348349350351352353354355356357358359360361362363364365366367368369370371372373374375376377378379380381382383384385386387388389390391392393394395396397398399400401402403404405406407408409410411412413414415416417418419420421422423424425426427428429430431432433434435436437438439440441442443444445446447448449450451452453454455456457458459460461462463464465466467468469470471472473474475476477478479480481482483484485486487488489490491492493494495496497498499500501502503504505506507508509510511512513514515516517518519520521522523524525526527528529530531532533534535536537538539540541542543544545546547548549550551552553554555556557558559560561562563564565566567568569570571572573574 |
- =========================================
- How to get printk format specifiers right
- =========================================
- .. _printk-specifiers:
- :Author: Randy Dunlap <rdunlap@infradead.org>
- :Author: Andrew Murray <amurray@mpc-data.co.uk>
- Integer types
- =============
- ::
- If variable is of Type, use printk format specifier:
- ------------------------------------------------------------
- char %d or %x
- unsigned char %u or %x
- short int %d or %x
- unsigned short int %u or %x
- int %d or %x
- unsigned int %u or %x
- long %ld or %lx
- unsigned long %lu or %lx
- long long %lld or %llx
- unsigned long long %llu or %llx
- size_t %zu or %zx
- ssize_t %zd or %zx
- s8 %d or %x
- u8 %u or %x
- s16 %d or %x
- u16 %u or %x
- s32 %d or %x
- u32 %u or %x
- s64 %lld or %llx
- u64 %llu or %llx
- If <type> is dependent on a config option for its size (e.g., sector_t,
- blkcnt_t) or is architecture-dependent for its size (e.g., tcflag_t), use a
- format specifier of its largest possible type and explicitly cast to it.
- Example::
- printk("test: sector number/total blocks: %llu/%llu\n",
- (unsigned long long)sector, (unsigned long long)blockcount);
- Reminder: sizeof() returns type size_t.
- The kernel's printf does not support %n. Floating point formats (%e, %f,
- %g, %a) are also not recognized, for obvious reasons. Use of any
- unsupported specifier or length qualifier results in a WARN and early
- return from vsnprintf().
- Pointer types
- =============
- A raw pointer value may be printed with %p which will hash the address
- before printing. The kernel also supports extended specifiers for printing
- pointers of different types.
- Some of the extended specifiers print the data on the given address instead
- of printing the address itself. In this case, the following error messages
- might be printed instead of the unreachable information::
- (null) data on plain NULL address
- (efault) data on invalid address
- (einval) invalid data on a valid address
- Plain Pointers
- --------------
- ::
- %p abcdef12 or 00000000abcdef12
- Pointers printed without a specifier extension (i.e unadorned %p) are
- hashed to prevent leaking information about the kernel memory layout. This
- has the added benefit of providing a unique identifier. On 64-bit machines
- the first 32 bits are zeroed. The kernel will print ``(ptrval)`` until it
- gathers enough entropy. If you *really* want the address see %px below.
- Error Pointers
- --------------
- ::
- %pe -ENOSPC
- For printing error pointers (i.e. a pointer for which IS_ERR() is true)
- as a symbolic error name. Error values for which no symbolic name is
- known are printed in decimal, while a non-ERR_PTR passed as the
- argument to %pe gets treated as ordinary %p.
- Symbols/Function Pointers
- -------------------------
- ::
- %pS versatile_init+0x0/0x110
- %ps versatile_init
- %pSR versatile_init+0x9/0x110
- (with __builtin_extract_return_addr() translation)
- %pB prev_fn_of_versatile_init+0x88/0x88
- The ``S`` and ``s`` specifiers are used for printing a pointer in symbolic
- format. They result in the symbol name with (S) or without (s)
- offsets. If KALLSYMS are disabled then the symbol address is printed instead.
- The ``B`` specifier results in the symbol name with offsets and should be
- used when printing stack backtraces. The specifier takes into
- consideration the effect of compiler optimisations which may occur
- when tail-calls are used and marked with the noreturn GCC attribute.
- Probed Pointers from BPF / tracing
- ----------------------------------
- ::
- %pks kernel string
- %pus user string
- The ``k`` and ``u`` specifiers are used for printing prior probed memory from
- either kernel memory (k) or user memory (u). The subsequent ``s`` specifier
- results in printing a string. For direct use in regular vsnprintf() the (k)
- and (u) annotation is ignored, however, when used out of BPF's bpf_trace_printk(),
- for example, it reads the memory it is pointing to without faulting.
- Kernel Pointers
- ---------------
- ::
- %pK 01234567 or 0123456789abcdef
- For printing kernel pointers which should be hidden from unprivileged
- users. The behaviour of %pK depends on the kptr_restrict sysctl - see
- Documentation/admin-guide/sysctl/kernel.rst for more details.
- Unmodified Addresses
- --------------------
- ::
- %px 01234567 or 0123456789abcdef
- For printing pointers when you *really* want to print the address. Please
- consider whether or not you are leaking sensitive information about the
- kernel memory layout before printing pointers with %px. %px is functionally
- equivalent to %lx (or %lu). %px is preferred because it is more uniquely
- grep'able. If in the future we need to modify the way the kernel handles
- printing pointers we will be better equipped to find the call sites.
- Pointer Differences
- -------------------
- ::
- %td 2560
- %tx a00
- For printing the pointer differences, use the %t modifier for ptrdiff_t.
- Example::
- printk("test: difference between pointers: %td\n", ptr2 - ptr1);
- Struct Resources
- ----------------
- ::
- %pr [mem 0x60000000-0x6fffffff flags 0x2200] or
- [mem 0x0000000060000000-0x000000006fffffff flags 0x2200]
- %pR [mem 0x60000000-0x6fffffff pref] or
- [mem 0x0000000060000000-0x000000006fffffff pref]
- For printing struct resources. The ``R`` and ``r`` specifiers result in a
- printed resource with (R) or without (r) a decoded flags member.
- Passed by reference.
- Physical address types phys_addr_t
- ----------------------------------
- ::
- %pa[p] 0x01234567 or 0x0123456789abcdef
- For printing a phys_addr_t type (and its derivatives, such as
- resource_size_t) which can vary based on build options, regardless of the
- width of the CPU data path.
- Passed by reference.
- DMA address types dma_addr_t
- ----------------------------
- ::
- %pad 0x01234567 or 0x0123456789abcdef
- For printing a dma_addr_t type which can vary based on build options,
- regardless of the width of the CPU data path.
- Passed by reference.
- Raw buffer as an escaped string
- -------------------------------
- ::
- %*pE[achnops]
- For printing raw buffer as an escaped string. For the following buffer::
- 1b 62 20 5c 43 07 22 90 0d 5d
- A few examples show how the conversion would be done (excluding surrounding
- quotes)::
- %*pE "\eb \C\a"\220\r]"
- %*pEhp "\x1bb \C\x07"\x90\x0d]"
- %*pEa "\e\142\040\\\103\a\042\220\r\135"
- The conversion rules are applied according to an optional combination
- of flags (see :c:func:`string_escape_mem` kernel documentation for the
- details):
- - a - ESCAPE_ANY
- - c - ESCAPE_SPECIAL
- - h - ESCAPE_HEX
- - n - ESCAPE_NULL
- - o - ESCAPE_OCTAL
- - p - ESCAPE_NP
- - s - ESCAPE_SPACE
- By default ESCAPE_ANY_NP is used.
- ESCAPE_ANY_NP is the sane choice for many cases, in particularly for
- printing SSIDs.
- If field width is omitted then 1 byte only will be escaped.
- Raw buffer as a hex string
- --------------------------
- ::
- %*ph 00 01 02 ... 3f
- %*phC 00:01:02: ... :3f
- %*phD 00-01-02- ... -3f
- %*phN 000102 ... 3f
- For printing small buffers (up to 64 bytes long) as a hex string with a
- certain separator. For larger buffers consider using
- :c:func:`print_hex_dump`.
- MAC/FDDI addresses
- ------------------
- ::
- %pM 00:01:02:03:04:05
- %pMR 05:04:03:02:01:00
- %pMF 00-01-02-03-04-05
- %pm 000102030405
- %pmR 050403020100
- For printing 6-byte MAC/FDDI addresses in hex notation. The ``M`` and ``m``
- specifiers result in a printed address with (M) or without (m) byte
- separators. The default byte separator is the colon (:).
- Where FDDI addresses are concerned the ``F`` specifier can be used after
- the ``M`` specifier to use dash (-) separators instead of the default
- separator.
- For Bluetooth addresses the ``R`` specifier shall be used after the ``M``
- specifier to use reversed byte order suitable for visual interpretation
- of Bluetooth addresses which are in the little endian order.
- Passed by reference.
- IPv4 addresses
- --------------
- ::
- %pI4 1.2.3.4
- %pi4 001.002.003.004
- %p[Ii]4[hnbl]
- For printing IPv4 dot-separated decimal addresses. The ``I4`` and ``i4``
- specifiers result in a printed address with (i4) or without (I4) leading
- zeros.
- The additional ``h``, ``n``, ``b``, and ``l`` specifiers are used to specify
- host, network, big or little endian order addresses respectively. Where
- no specifier is provided the default network/big endian order is used.
- Passed by reference.
- IPv6 addresses
- --------------
- ::
- %pI6 0001:0002:0003:0004:0005:0006:0007:0008
- %pi6 00010002000300040005000600070008
- %pI6c 1:2:3:4:5:6:7:8
- For printing IPv6 network-order 16-bit hex addresses. The ``I6`` and ``i6``
- specifiers result in a printed address with (I6) or without (i6)
- colon-separators. Leading zeros are always used.
- The additional ``c`` specifier can be used with the ``I`` specifier to
- print a compressed IPv6 address as described by
- https://tools.ietf.org/html/rfc5952
- Passed by reference.
- IPv4/IPv6 addresses (generic, with port, flowinfo, scope)
- ---------------------------------------------------------
- ::
- %pIS 1.2.3.4 or 0001:0002:0003:0004:0005:0006:0007:0008
- %piS 001.002.003.004 or 00010002000300040005000600070008
- %pISc 1.2.3.4 or 1:2:3:4:5:6:7:8
- %pISpc 1.2.3.4:12345 or [1:2:3:4:5:6:7:8]:12345
- %p[Ii]S[pfschnbl]
- For printing an IP address without the need to distinguish whether it's of
- type AF_INET or AF_INET6. A pointer to a valid struct sockaddr,
- specified through ``IS`` or ``iS``, can be passed to this format specifier.
- The additional ``p``, ``f``, and ``s`` specifiers are used to specify port
- (IPv4, IPv6), flowinfo (IPv6) and scope (IPv6). Ports have a ``:`` prefix,
- flowinfo a ``/`` and scope a ``%``, each followed by the actual value.
- In case of an IPv6 address the compressed IPv6 address as described by
- https://tools.ietf.org/html/rfc5952 is being used if the additional
- specifier ``c`` is given. The IPv6 address is surrounded by ``[``, ``]`` in
- case of additional specifiers ``p``, ``f`` or ``s`` as suggested by
- https://tools.ietf.org/html/draft-ietf-6man-text-addr-representation-07
- In case of IPv4 addresses, the additional ``h``, ``n``, ``b``, and ``l``
- specifiers can be used as well and are ignored in case of an IPv6
- address.
- Passed by reference.
- Further examples::
- %pISfc 1.2.3.4 or [1:2:3:4:5:6:7:8]/123456789
- %pISsc 1.2.3.4 or [1:2:3:4:5:6:7:8]%1234567890
- %pISpfc 1.2.3.4:12345 or [1:2:3:4:5:6:7:8]:12345/123456789
- UUID/GUID addresses
- -------------------
- ::
- %pUb 00010203-0405-0607-0809-0a0b0c0d0e0f
- %pUB 00010203-0405-0607-0809-0A0B0C0D0E0F
- %pUl 03020100-0504-0706-0809-0a0b0c0e0e0f
- %pUL 03020100-0504-0706-0809-0A0B0C0E0E0F
- For printing 16-byte UUID/GUIDs addresses. The additional ``l``, ``L``,
- ``b`` and ``B`` specifiers are used to specify a little endian order in
- lower (l) or upper case (L) hex notation - and big endian order in lower (b)
- or upper case (B) hex notation.
- Where no additional specifiers are used the default big endian
- order with lower case hex notation will be printed.
- Passed by reference.
- dentry names
- ------------
- ::
- %pd{,2,3,4}
- %pD{,2,3,4}
- For printing dentry name; if we race with :c:func:`d_move`, the name might
- be a mix of old and new ones, but it won't oops. %pd dentry is a safer
- equivalent of %s dentry->d_name.name we used to use, %pd<n> prints ``n``
- last components. %pD does the same thing for struct file.
- Passed by reference.
- block_device names
- ------------------
- ::
- %pg sda, sda1 or loop0p1
- For printing name of block_device pointers.
- struct va_format
- ----------------
- ::
- %pV
- For printing struct va_format structures. These contain a format string
- and va_list as follows::
- struct va_format {
- const char *fmt;
- va_list *va;
- };
- Implements a "recursive vsnprintf".
- Do not use this feature without some mechanism to verify the
- correctness of the format string and va_list arguments.
- Passed by reference.
- Device tree nodes
- -----------------
- ::
- %pOF[fnpPcCF]
- For printing device tree node structures. Default behaviour is
- equivalent to %pOFf.
- - f - device node full_name
- - n - device node name
- - p - device node phandle
- - P - device node path spec (name + @unit)
- - F - device node flags
- - c - major compatible string
- - C - full compatible string
- The separator when using multiple arguments is ':'
- Examples::
- %pOF /foo/bar@0 - Node full name
- %pOFf /foo/bar@0 - Same as above
- %pOFfp /foo/bar@0:10 - Node full name + phandle
- %pOFfcF /foo/bar@0:foo,device:--P- - Node full name +
- major compatible string +
- node flags
- D - dynamic
- d - detached
- P - Populated
- B - Populated bus
- Passed by reference.
- Fwnode handles
- --------------
- ::
- %pfw[fP]
- For printing information on fwnode handles. The default is to print the full
- node name, including the path. The modifiers are functionally equivalent to
- %pOF above.
- - f - full name of the node, including the path
- - P - the name of the node including an address (if there is one)
- Examples (ACPI)::
- %pfwf \_SB.PCI0.CIO2.port@1.endpoint@0 - Full node name
- %pfwP endpoint@0 - Node name
- Examples (OF)::
- %pfwf /ocp@68000000/i2c@48072000/camera@10/port/endpoint - Full name
- %pfwP endpoint - Node name
- Time and date
- -------------
- ::
- %pt[RT] YYYY-mm-ddTHH:MM:SS
- %pt[RT]d YYYY-mm-dd
- %pt[RT]t HH:MM:SS
- %pt[RT][dt][r]
- For printing date and time as represented by::
- R struct rtc_time structure
- T time64_t type
- in human readable format.
- By default year will be incremented by 1900 and month by 1.
- Use %pt[RT]r (raw) to suppress this behaviour.
- Passed by reference.
- struct clk
- ----------
- ::
- %pC pll1
- %pCn pll1
- For printing struct clk structures. %pC and %pCn print the name of the clock
- (Common Clock Framework) or a unique 32-bit ID (legacy clock framework).
- Passed by reference.
- bitmap and its derivatives such as cpumask and nodemask
- -------------------------------------------------------
- ::
- %*pb 0779
- %*pbl 0,3-6,8-10
- For printing bitmap and its derivatives such as cpumask and nodemask,
- %*pb outputs the bitmap with field width as the number of bits and %*pbl
- output the bitmap as range list with field width as the number of bits.
- Passed by reference.
- Flags bitfields such as page flags, gfp_flags
- ---------------------------------------------
- ::
- %pGp referenced|uptodate|lru|active|private
- %pGg GFP_USER|GFP_DMA32|GFP_NOWARN
- %pGv read|exec|mayread|maywrite|mayexec|denywrite
- For printing flags bitfields as a collection of symbolic constants that
- would construct the value. The type of flags is given by the third
- character. Currently supported are [p]age flags, [v]ma_flags (both
- expect ``unsigned long *``) and [g]fp_flags (expects ``gfp_t *``). The flag
- names and print order depends on the particular type.
- Note that this format should not be used directly in the
- :c:func:`TP_printk()` part of a tracepoint. Instead, use the show_*_flags()
- functions from <trace/events/mmflags.h>.
- Passed by reference.
- Network device features
- -----------------------
- ::
- %pNF 0x000000000000c000
- For printing netdev_features_t.
- Passed by reference.
- Thanks
- ======
- If you add other %p extensions, please extend <lib/test_printf.c> with
- one or more test cases, if at all feasible.
- Thank you for your cooperation and attention.
|