diff options
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/printk-formats.txt | 31 |
1 files changed, 28 insertions, 3 deletions
diff --git a/Documentation/printk-formats.txt b/Documentation/printk-formats.txt index 361789df51ec..aa0a776c817a 100644 --- a/Documentation/printk-formats.txt +++ b/Documentation/printk-formats.txt @@ -5,7 +5,6 @@ How to get printk format specifiers right :Author: Randy Dunlap <rdunlap@infradead.org> :Author: Andrew Murray <amurray@mpc-data.co.uk> - Integer types ============= @@ -45,6 +44,18 @@ return from vsnprintf. Raw pointer value SHOULD be printed with %p. The kernel supports the following extended format specifiers for 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. + +:: + + %p abcdef12 or 00000000abcdef12 + Symbols/Function Pointers ========================= @@ -85,18 +96,32 @@ Examples:: printk("Faulted at %pS\n", (void *)regs->ip); printk(" %s%pB\n", (reliable ? "" : "? "), (void *)*stack); - Kernel Pointers =============== :: - %pK 0x01234567 or 0x0123456789abcdef + %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 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. + Struct Resources ================ |