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printk-formats.txt: Better describe the difference between %pS and %pF 

Sometimes people seems unclear when to use the %pS or %pF printk format.
For example, see commit 51d96dc2e2 ("random: fix warning message on ia64
and parisc") which fixed such a wrong format string.

The documentation should be more clear about the difference.

Signed-off-by: Helge Deller <deller@gmx.de>
[pmladek@suse.com: Restructure the entire section]
Signed-off-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Helge Deller <deller@gmx.de>
This commit is contained in:
Helge Deller 2017-08-15 11:34:19 +02:00
parent 4098116039
commit d6957f3396
1 changed files with 11 additions and 8 deletions
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19
Documentation/printk-formats.txt
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@ -58,20 +58,23 @@ Symbols/Function Pointers
%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 ``F`` and ``f`` specifiers are for printing function pointers,
for example, f->func, &gettimeofday. They have the same result as
``S`` and ``s`` specifiers. But they do an extra conversion on
ia64, ppc64 and parisc64 architectures where the function pointers
are actually function descriptors.
The ``S`` and ``s`` specifiers can be used for printing symbols
from direct addresses, for example, __builtin_return_address(0),
(void *)regs->ip. They result in the symbol name with (``S``) or
without (``s``) offsets. If KALLSYMS are disabled then 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
===============