内核里printk打印指针打印出(____ptrval____)

在调试内核的时候，打印一个指针tmp：

printk(KERN_INFO "tmp addr: %p\n", tmp);

打印出来经常是：(____ptrval____)，用%px可以打印地址。

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.

Symbols/Function Pointers
%pS     versatile_init+0x0/0x110
%ps     versatile_init
%pF     versatile_init+0x0/0x110
%pf     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.

Note, that the F and f specifiers are identical to S (s) and thus deprecated. We have F and f because on ia64, ppc64 and parisc64 function pointers are indirect and, in fact, are function descriptors, which require additional dereferencing before we can lookup the symbol. As of now, S and s perform dereferencing on those platforms (when needed), so F and f exist for compatibility reasons only.

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.

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/sysctl/kernel.txt 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.