vsprintf: add printk specifier %px

[sfrench/cifs-2.6.git] / Documentation / printk-formats.txt

diff --git a/Documentation/printk-formats.txt b/Documentation/printk-formats.txt
index b4e668ac4fe33e5b6c05fdfc12266a92baabd327..aa0a776c817a7ceabb217c3eecc31ecdb32f59c7 100644 (file)
--- a/Documentation/printk-formats.txt
+++ b/Documentation/printk-formats.txt
@@ -49,7 +49,8 @@ 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.
+space. On 64 bit machines the first 32 bits are zeroed. If you _really_
+want the address see %px below.
 
 ::
 
@@ -106,6 +107,21 @@ 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
 ================