Commit d6957f33 authored by Helge Deller's avatar Helge Deller

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 51d96dc2 ("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: default avatarHelge Deller <deller@gmx.de>
[pmladek@suse.com: Restructure the entire section]
Signed-off-by: default avatarPetr Mladek <pmladek@suse.com>
Reviewed-by: default avatarSergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: default avatarHelge Deller <deller@gmx.de>
parent 40981160
...@@ -58,20 +58,23 @@ Symbols/Function Pointers ...@@ -58,20 +58,23 @@ Symbols/Function Pointers
%ps versatile_init %ps versatile_init
%pB prev_fn_of_versatile_init+0x88/0x88 %pB prev_fn_of_versatile_init+0x88/0x88
For printing symbols and function pointers. The ``S`` and ``s`` specifiers The ``F`` and ``f`` specifiers are for printing function pointers,
result in the symbol name with (``S``) or without (``s``) offsets. Where for example, f->func, &gettimeofday. They have the same result as
this is used on a kernel without KALLSYMS - the symbol address is ``S`` and ``s`` specifiers. But they do an extra conversion on
printed instead. 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 The ``B`` specifier results in the symbol name with offsets and should be
used when printing stack backtraces. The specifier takes into used when printing stack backtraces. The specifier takes into
consideration the effect of compiler optimisations which may occur consideration the effect of compiler optimisations which may occur
when tail-call``s are used and marked with the noreturn GCC attribute. 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 Kernel Pointers
=============== ===============
......
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