Merge tag 'gvt-next-2017-12-14' of https://github.com/intel/gvt-linux into drm-intel...

[linux.git] / Documentation / printk-formats.txt

diff --git a/Documentation/printk-formats.txt b/Documentation/printk-formats.txt
index 361789df51ecf58d5083436792588d2f12faa7f2..aa0a776c817a7ceabb217c3eecc31ecdb32f59c7 100644 (file)
--- 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
 ================