原文地址：http://elinux.org/Debugging_by_printing#Usage 

If variable is of Type,		use printk format specifier:
---------------------------------------------------------
		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

Raw pointer value SHOULD be printed with %p. The kernel supports
the following extended format specifiers for pointer types:

Symbols/Function Pointers:

	%pF	versatile_init+0x0/0x110
	%pf	versatile_init
	%pS	versatile_init+0x0/0x110
	%pSR	versatile_init+0x9/0x110
		(with __builtin_extract_return_addr() translation)
	%ps	versatile_init
	%pB	prev_fn_of_versatile_init+0x88/0x88

	For printing symbols and function pointers. The ‘S‘ and ‘s‘ specifiers
	result in the symbol name with (‘S‘) or without (‘s‘) offsets. Where
	this is used on a kernel without KALLSYMS - 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.

	On ia64, ppc64 and parisc64 architectures function pointers are
	actually function descriptors which must first be resolved. The ‘F‘ and
	‘f‘ specifiers perform this resolution and then provide the same
	functionality as the ‘S‘ and ‘s‘ specifiers.

Kernel Pointers:

	%pK	0x01234567 or 0x0123456789abcdef

	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.

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.

Physical addresses:

	%pa	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.


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

IPv4 addresses:

	%pI4	1.2.3.4
	%pi4	001.002.003.004
	%p[Ii][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.

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
	http://tools.ietf.org/html/rfc5952

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 characters - and big endian order
	in lower (‘b‘) or upper case (‘B‘) hex characters.

	Where no additional specifiers are used the default little endian
	order with lower case hex characters will be printed.

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;
	};

	Do not use this feature without some mechanism to verify the
	correctness of the format string and va_list arguments.

u64 SHOULD be printed with %llu/%llx, (unsigned long long):

	printk("%llu", (unsigned long long)u64_var);

s64 SHOULD be printed with %lld/%llx, (long long):

	printk("%lld", (long long)s64_var);

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.

Thank you for your cooperation and attention.

Reference:

http://elinux.org/Kernel_Debugging_Tips#Using_a_kernel_debugger  

http://blog.csdn.net/yihui8/article/details/6736679  

By Randy Dunlap <rdunlap@infradead.org> and
Andrew Murray <amurray@mpc-data.co.uk>