[kernel-hardening] [PATCH v3 1/3] doc: convert printk-formats.txt to rst

Tobin C. Harding
2017-12-18T22:29:03Z

Documentation/printk-formats.txt is a candidate for conversion to
ReStructuredText format. Some effort has already been made to do this
conversion even thought the suffix is currently .txt

Changes required to complete conversion

- Move printk-formats.txt to core-api/printk-formats.rst
- Add entry to Documentation/core-api/index.rst
- Remove entry from Documentation/00-INDEX
- Fix minor grammatical errors.
- Order heading adornments as suggested by rst docs.
- Use 'Passed by reference' uniformly.
- Update pointer documentation around %px specifier.
- Fix erroneous double backticks (to commas).
- Remove extraneous double backticks (suggested by Jonathan Corbet).
- Simplify documentation for kobject.

Signed-off-by: Tobin C. Harding <me@tobin.cc>
---
Documentation/00-INDEX | 2 -
Documentation/core-api/index.rst | 1 +
.../printk-formats.rst} | 229 +++++++++++----------
lib/vsprintf.c | 3 +-
4 files changed, 122 insertions(+), 113 deletions(-)
rename Documentation/{printk-formats.txt => core-api/printk-formats.rst} (63%)

diff --git a/Documentation/00-INDEX b/Documentation/00-INDEX
index 3bec49c33bbb..7023bfaec21c 100644
--- a/Documentation/00-INDEX
+++ b/Documentation/00-INDEX
@@ -346,8 +346,6 @@ prctl/
- directory with info on the priveledge control subsystem
preempt-locking.txt
- info on locking under a preemptive kernel.
-printk-formats.txt
- - how to get printk format specifiers right
process/
- how to work with the mainline kernel development process.
pps/
diff --git a/Documentation/core-api/index.rst b/Documentation/core-api/index.rst
index d4d54b05d6c5..d55ee6b006ed 100644
--- a/Documentation/core-api/index.rst
+++ b/Documentation/core-api/index.rst
@@ -22,6 +22,7 @@ Core utilities
flexible-arrays
librs
genalloc
+ printk-formats

Interfaces for kernel debugging
===============================
diff --git a/Documentation/printk-formats.txt b/Documentation/core-api/printk-formats.rst
similarity index 63%
rename from Documentation/printk-formats.txt
rename to Documentation/core-api/printk-formats.rst
index aa0a776c817a..2c542e30b13b 100644
--- a/Documentation/printk-formats.txt
+++ b/Documentation/core-api/printk-formats.rst
@@ -5,6 +5,7 @@ How to get printk format specifiers right
:Author: Randy Dunlap <rdunlap@infradead.org>
:Author: Andrew Murray <amurray@mpc-data.co.uk>

+
Integer types
=============

@@ -25,39 +26,45 @@ Integer types
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.
+
+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()`` result is of type ``size_t``.
+Reminder: sizeof() returns type size_t.

-The kernel's printf does not support ``%n``. For obvious reasons, floating
-point formats (``%e, %f, %g, %a``) are also not recognized. Use of any
+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.
-
-Raw pointer value SHOULD be printed with %p. The kernel supports
-the following extended format specifiers for pointer types:
+return from vsnprintf().

-Pointer Types
+Pointer types
=============

-Pointers printed without a specifier extension (i.e unadorned %p) are
-hashed to give a unique identifier without leaking kernel addresses to user
-space. On 64 bit machines the first 32 bits are zeroed. If you _really_
-want the address see %px below.
+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.
+
+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. If you *really* want the address see %px
+below.
+
Symbols/Function Pointers
-=========================
+-------------------------

::

@@ -69,6 +76,7 @@ Symbols/Function Pointers
%ps versatile_init
%pB prev_fn_of_versatile_init+0x88/0x88

+
The ``F`` and ``f`` specifiers are for printing function pointers,
for example, f->func, &gettimeofday. They have the same result as
``S`` and ``s`` specifiers. But they do an extra conversion on
@@ -77,14 +85,14 @@ are actually function descriptors.

The ``S`` and ``s`` specifiers can be used for printing symbols
from direct addresses, for example, __builtin_return_address(0),
-(void *)regs->ip. They result in the symbol name with (``S``) or
-without (``s``) offsets. If KALLSYMS are disabled then the symbol
+(void *)regs->ip. 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-call``s are used and marked with the noreturn GCC attribute.
+when tail-calls are used and marked with the noreturn GCC attribute.

Examples::

@@ -97,33 +105,32 @@ Examples::
printk(" %s%pB\n", (reliable ? "" : "? "), (void *)*stack);

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
+For printing Kernel pointers which should be hidden from unprivileged
+users. The behaviour of %pK depends on the kptr_restrict sysctl - see
Documentation/sysctl/kernel.txt for more details.

Unmodified Addresses
-====================
+--------------------

::

%px 01234567 or 0123456789abcdef

-For printing pointers when you _really_ want to print the address. Please
+For printing pointers when you *really* want to print the address. Please
consider whether or not you are leaking sensitive information about the
-Kernel layout in memory before printing pointers with %px. %px is
-functionally equivalent to %lx. %px is preferred to %lx because it is more
-uniquely grep'able. If, in the future, we need to modify the way the Kernel
-handles printing pointers it will be nice to be able to find the call
-sites.
+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.

Struct Resources
-================
+----------------

::

@@ -133,32 +140,37 @@ Struct Resources
[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.
+printed resource with (R) or without (r) a decoded flags member.
+
Passed by reference.

-Physical addresses types ``phys_addr_t``
-========================================
+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.
+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 addresses types ``dma_addr_t``
-==================================
+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.
+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
-===============================
+-------------------------------

::

@@ -168,8 +180,8 @@ For printing raw buffer as an escaped string. For the following buffer::

1b 62 20 5c 43 07 22 90 0d 5d

-few examples show how the conversion would be done (the result string
-without surrounding quotes)::
+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]"
@@ -179,23 +191,23 @@ 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
+ - 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 the 1 byte only will be escaped.
+If field width is omitted then 1 byte only will be escaped.

Raw buffer as a hex string
-==========================
+--------------------------

::

@@ -204,12 +216,12 @@ Raw buffer as a hex string
%*phD 00-01-02- ... -3f
%*phN 000102 ... 3f

-For printing a small buffers (up to 64 bytes long) as a hex string with
-certain separator. For the larger buffers consider to use
+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
-==================
+------------------

::

@@ -220,11 +232,11 @@ MAC/FDDI addresses
%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 (``:``).
+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
+the ``M`` specifier to use dash (-) separators instead of the default
separator.

For Bluetooth addresses the ``R`` specifier shall be used after the ``M``
@@ -234,7 +246,7 @@ of Bluetooth addresses which are in the little endian order.
Passed by reference.

IPv4 addresses
-==============
+--------------

::

@@ -243,8 +255,8 @@ IPv4 addresses
%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.
+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
@@ -253,7 +265,7 @@ no specifier is provided the default network/big endian order is used.
Passed by reference.

IPv6 addresses
-==============
+--------------

::

@@ -262,7 +274,7 @@ IPv6 addresses
%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``)
+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
@@ -272,7 +284,7 @@ http://tools.ietf.org/html/rfc5952
Passed by reference.

IPv4/IPv6 addresses (generic, with port, flowinfo, scope)
-=========================================================
+---------------------------------------------------------

::

@@ -282,8 +294,8 @@ IPv4/IPv6 addresses (generic, with port, flowinfo, scope)
%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``,
+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
@@ -309,7 +321,7 @@ Further examples::
%pISpfc 1.2.3.4:12345 or [1:2:3:4:5:6:7:8]:12345/123456789

UUID/GUID addresses
-===================
+-------------------

::

@@ -318,33 +330,33 @@ UUID/GUID addresses
%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 characters - and big endian order
-in lower ('b') or upper case ('B') hex characters.
+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 characters will be printed.
+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.
+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
-==================
+------------------

::

@@ -353,7 +365,7 @@ block_device names
For printing name of block_device pointers.

struct va_format
-================
+----------------

::

@@ -375,31 +387,27 @@ correctness of the format string and va_list arguments.
Passed by reference.

kobjects
-========
+--------

::

- %pO
+ %pOF[fnpPcCF]

- Base specifier for kobject based structs. Must be followed with
- character for specific type of kobject as listed below:

- Device tree nodes:
+For printing kobject based structs (device nodes). Default behaviour is
+equivalent to %pOFf.

- %pOF[fnpPcCF]
+ - 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

- For printing device tree nodes. The optional arguments are:
- 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
- Without any arguments prints full_name (same as %pOFf)
- The separator when using multiple arguments is ':'
+The separator when using multiple arguments is ':'

- Examples:
+Examples::

%pOF /foo/bar@0 - Node full name
%pOFf /foo/bar@0 - Same as above
@@ -412,11 +420,10 @@ kobjects
P - Populated
B - Populated bus

- Passed by reference.
-
+Passed by reference.

struct clk
-==========
+----------

::

@@ -424,14 +431,14 @@ struct clk
%pCn pll1
%pCr 1560000000

-For printing struct clk structures. ``%pC`` and ``%pCn`` print the name
+For printing struct clk structures. %pC and %pCn print the name
(Common Clock Framework) or address (legacy clock framework) of the
-structure; ``%pCr`` prints the current clock rate.
+structure; %pCr prints the current clock rate.

Passed by reference.

bitmap and its derivatives such as cpumask and nodemask
-=======================================================
+-------------------------------------------------------

::

@@ -439,13 +446,13 @@ bitmap and its derivatives such as cpumask and nodemask
%*pbl 0,3-6,8-10

For printing bitmap and its derivatives such as cpumask and nodemask,
-``%*pb`` output the bitmap with field width as the number of bits and ``%*pbl``
+%*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
-=============================================
+---------------------------------------------

::

@@ -459,14 +466,14 @@ 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 :c:func:`TP_printk()` part
-of a tracepoint. Instead, use the ``show_*_flags()`` functions from
-<trace/events/mmflags.h>.
+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
-=======================
+-----------------------

::

@@ -476,8 +483,10 @@ For printing netdev_features_t.

Passed by reference.

-If you add other ``%p`` extensions, please extend lib/test_printf.c with
-one or more test cases, if at all feasible.
+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.
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 01c3957b2de6..6ec0844ab5d1 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -1834,7 +1834,8 @@ static char *ptr_to_id(char *buf, char *end, void *ptr, struct printf_spec spec)
*
* - 'x' For printing the address. Equivalent to "%lx".
*
- * ** Please update also Documentation/printk-formats.txt when making changes **
+ * ** When making changes please also update:
+ * Documentation/core-api/printk-formats.rst
*
* Note: The difference between 'S' and 'F' is that on ia64 and ppc64
* function pointers are really function descriptors, which contain a
--
2.7.4