linux-kernel - Re: [PATCH v4 07/11] lib/vsprintf: Remove support for %pF and %pf in favour of %pS and %ps

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Message-ID: <20190902143935.xtd44jdvhjuc2wxe@pathway.suse.cz>
Date:   Mon, 2 Sep 2019 16:39:35 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Sakari Ailus <sakari.ailus@...ux.intel.com>
Cc:     rafael@...nel.org, linux-kernel@...r.kernel.org,
        Rob Herring <robh@...nel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        devicetree@...r.kernel.org, linux-acpi@...r.kernel.org,
        Steven Rostedt <rostedt@...dmis.org>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Tzvetomir Stoyanov <tstoyanov@...are.com>,
        linux-trace-devel@...r.kernel.org, Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>
Subject: Re: [PATCH v4 07/11] lib/vsprintf: Remove support for %pF and %pf in
 favour of %pS and %ps

On Mon 2019-09-02 11:32:36, Sakari Ailus wrote:
> %pS and %ps are now the preferred conversion specifiers to print function
> names. The functionality is equivalent; remove the old, deprecated %pF
> and %pf support.

Hmm, I see the following in master:

$> git grep %pF
tools/lib/traceevent/Documentation/libtraceevent-func_apis.txt:or events have "%pF" or "%pS" parameter in its format string. It is common to

$> git grep %pf
tools/lib/traceevent/event-parse.c:             if (asprintf(&format, "%%pf: (NO FORMAT FOUND at %llx)\n", addr) < 0)
tools/lib/traceevent/event-parse.c:     if (asprintf(&format, "%s: %s", "%pf", printk->printk) < 0)

I wonder how this is related to printk(). In each case, it seems
that libtraceevent somehow implements the non-standard kernel
%p mofifiers. It looks error-prone to keep another %pf user
with the old semantic around.

I am adding some tracing people into CC.

Best Regards,
Petr

> Signed-off-by: Sakari Ailus <sakari.ailus@...ux.intel.com>
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> ---
>  Documentation/core-api/printk-formats.rst | 10 ----------
>  lib/vsprintf.c                            |  8 ++------
>  scripts/checkpatch.pl                     |  1 -
>  3 files changed, 2 insertions(+), 17 deletions(-)
> 
> diff --git a/Documentation/core-api/printk-formats.rst b/Documentation/core-api/printk-formats.rst
> index c6224d039bcbe..922a29eb70e6c 100644
> --- a/Documentation/core-api/printk-formats.rst
> +++ b/Documentation/core-api/printk-formats.rst
> @@ -86,8 +86,6 @@ Symbols/Function Pointers
>  
>  	%pS	versatile_init+0x0/0x110
>  	%ps	versatile_init
> -	%pF	versatile_init+0x0/0x110
> -	%pf	versatile_init
>  	%pSR	versatile_init+0x9/0x110
>  		(with __builtin_extract_return_addr() translation)
>  	%pB	prev_fn_of_versatile_init+0x88/0x88
> @@ -97,14 +95,6 @@ The ``S`` and ``s`` specifiers are used for printing a pointer in symbolic
>  format. They result in the symbol name with (S) or without (s)
>  offsets. If KALLSYMS are disabled then the symbol address is printed instead.
>  
> -Note, that the ``F`` and ``f`` specifiers are identical to ``S`` (``s``)
> -and thus deprecated. We have ``F`` and ``f`` because on ia64, ppc64 and
> -parisc64 function pointers are indirect and, in fact, are function
> -descriptors, which require additional dereferencing before we can lookup
> -the symbol. As of now, ``S`` and ``s`` perform dereferencing on those
> -platforms (when needed), so ``F`` and ``f`` exist for compatibility
> -reasons only.
> -
>  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
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index b0967cf17137d..b00b57f9f911f 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -909,7 +909,7 @@ char *symbol_string(char *buf, char *end, void *ptr,
>  #ifdef CONFIG_KALLSYMS
>  	if (*fmt == 'B')
>  		sprint_backtrace(sym, value);
> -	else if (*fmt != 'f' && *fmt != 's')
> +	else if (*fmt != 's')
>  		sprint_symbol(sym, value);
>  	else
>  		sprint_symbol_no_offset(sym, value);
> @@ -2007,9 +2007,7 @@ static char *kobject_string(char *buf, char *end, void *ptr,
>   *
>   * - 'S' For symbolic direct pointers (or function descriptors) with offset
>   * - 's' For symbolic direct pointers (or function descriptors) without offset
> - * - 'F' Same as 'S'
> - * - 'f' Same as 's'
> - * - '[FfSs]R' as above with __builtin_extract_return_addr() translation
> + * - '[Ss]R' as above with __builtin_extract_return_addr() translation
>   * - 'B' For backtraced symbolic direct pointers with offset
>   * - 'R' For decoded struct resource, e.g., [mem 0x0-0x1f 64bit pref]
>   * - 'r' For raw struct resource, e.g., [mem 0x0-0x1f flags 0x201]
> @@ -2112,8 +2110,6 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
>  	      struct printf_spec spec)
>  {
>  	switch (*fmt) {
> -	case 'F':
> -	case 'f':
>  	case 'S':
>  	case 's':
>  		ptr = dereference_symbol_descriptor(ptr);
> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
> index 93a7edfe0f059..a60c241112cd4 100755
> --- a/scripts/checkpatch.pl
> +++ b/scripts/checkpatch.pl
> @@ -6012,7 +6012,6 @@ sub process {
>  					my $ext_type = "Invalid";
>  					my $use = "";
>  					if ($bad_specifier =~ /p[Ff]/) {
> -						$ext_type = "Deprecated";
>  						$use = " - use %pS instead";
>  						$use =~ s/pS/ps/ if ($bad_specifier =~ /pf/);
>  					}
> -- 
> 2.20.1
>