Message-ID: <57867813.8010608@osg.samsung.com>
Date:	Wed, 13 Jul 2016 18:19:15 +0100
From:	Luis de Bethencourt <luisbg@....samsung.com>
To:	Markus Mayer <markus.mayer@...adcom.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Chris Metcalf <cmetcalf@...hip.com>,
	Kees Cook <keescook@...omium.org>, devel@...verdev.osuosl.org,
	linux-scsi@...r.kernel.org, linux-pm@...r.kernel.org,
	nouveau@...ts.freedesktop.org, speakup@...ux-speakup.org,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	dri-devel@...ts.freedesktop.org, linux-acpi@...r.kernel.org,
	target-devel@...r.kernel.org
Subject: Re: [PATCH v3 1/7] lib: string: add functions to case-convert strings

On 11/07/16 23:46, Markus Mayer wrote:
> On 9 July 2016 at 08:30, Markus Mayer <markus.mayer@...adcom.com> wrote:
>> On 9 July 2016 at 05:04, Luis de Bethencourt <luisbg@....samsung.com> wrote:
>>> On 08/07/16 23:43, Markus Mayer wrote:
>>>> Add a collection of generic functions to convert strings to lowercase
>>>> or uppercase.
>>>>
>>>> Changing the case of a string (with or without copying it first) seems
>>>> to be a recurring requirement in the kernel that is currently being
>>>> solved by several duplicated implementations doing the same thing. This
>>>> change aims at reducing this code duplication.
>>>>
>>>> The new functions are
>>>>     void strlcpytoupper(char *dst, const char *src, size_t len);
>>>>     void strlcpytolower(char *dst, const char *src, size_t len);
>>>>     void strcpytoupper(char *dst, const char *src);
>>>>     void strcpytolower(char *dst, const char *src);
>>>>     void strtoupper(char *s);
>>>>     void strtolower(char *s);
>>>>
>>>> The "str[l]cpyto*" versions of the function take a destination string
>>>> and a source string as arguments. The "strlcpyto*" versions additionally
>>>> take a length argument like strlcpy() itself. Lastly, the strto*
>>>> functions take a single string argument and modify the passed-in string.
>>>>
>>>> Like strlcpy(), and unlike strncpy(), the functions guarantee NULL
>>>> termination of the destination string.
>>>>
>>>> Signed-off-by: Markus Mayer <mmayer@...adcom.com>
>>>> ---
>>>>  include/linux/string.h | 40 ++++++++++++++++++++++++++++++++++++++++
>>>>  lib/string.c           | 38 ++++++++++++++++++++++++++++++++++++++
>>>>  2 files changed, 78 insertions(+)
>>>>
>>>> diff --git a/include/linux/string.h b/include/linux/string.h
>>>> index 26b6f6a..36c9d14 100644
>>>> --- a/include/linux/string.h
>>>> +++ b/include/linux/string.h
>>>> @@ -116,6 +116,8 @@ extern void * memchr(const void *,int,__kernel_size_t);
>>>>  #endif
>>>>  void *memchr_inv(const void *s, int c, size_t n);
>>>>  char *strreplace(char *s, char old, char new);
>>>> +extern void strlcpytoupper(char *dst, const char *src, size_t len);
>>>> +extern void strlcpytolower(char *dst, const char *src, size_t len);
>>>>
>>>>  extern void kfree_const(const void *x);
>>>>
>>>> @@ -169,4 +171,42 @@ static inline const char *kbasename(const char *path)
>>>>       return tail ? tail + 1 : path;
>>>>  }
>>>>
>>>> +/**
>>>> + * strcpytoupper - Copy string and convert to uppercase.
>>>> + * @dst: The buffer to store the result.
>>>> + * @src: The string to convert to uppercase.
>>>> + */
>>>> +static inline void strcpytoupper(char *dst, const char *src)
>>>> +{
>>>> +     strlcpytoupper(dst, src, -1);
>>>> +}
>>>> +
>>>
>>> Why not use SIZE_MAX instead of -1?
>>
>> Sure. I'll change all four of them. Thanks.
> 
> Turns out there's actually a circular dependency here. SIZE_MAX is
> defined in linux/kernel.h. So, string.h would need to include
> kernel.h. But kernel.h, by way of several other headers, includes
> string.h.
> 
> Attempting to include kernel.h in string.h then leads to something like this:
> 
>   CHK     include/config/kernel.release
>   CHK     include/generated/uapi/linux/version.h
>   CHK     include/generated/utsrelease.h
>   CC      scripts/mod/devicetable-offsets.s
>   CHK     include/generated/timeconst.h
> In file included from include/linux/printk.h:289:0,
>                  from include/linux/kernel.h:13,
>                  from include/linux/string.h:11,
>                  from include/uapi/linux/uuid.h:21,
>                  from include/linux/uuid.h:19,
>                  from include/linux/mod_devicetable.h:12,
>                  from scripts/mod/devicetable-offsets.c:2:
> include/linux/dynamic_debug.h: In function ‘ddebug_dyndbg_module_param_cb’:
> include/linux/dynamic_debug.h:122:2: error: implicit declaration of
> function ‘strstr’ [-Werror=implicit-function-declaration]
>   if (strstr(param, "dyndbg")) {
>   ^
> include/linux/dynamic_debug.h:122:6: warning: incompatible implicit
> declaration of built-in function ‘strstr’ [enabled by default]
>   if (strstr(param, "dyndbg")) {
>       ^
> Since kernel.h is referencing string.h (which is needed, but not
> included a second time due to the include guards), this leads to
> undeclared string functions, because we are still in the early stages
> of including string.h itself and haven't gotten to the function
> declarations yet.
> 

Hi Markus,

Amazing. I see this happening as well, but I know it shouldn't.

The reason the #ifndef guards in headers are there is precisely to allow
circular dependencies.

The problem in your output reads as:
strstr() is in string.h
#include string.h -> that includes kernel.h -> that includes string.h

The third should do nothing based on _LINUX_STRING_H_ being defined already
and all code inside the #ifndef in string.h not being executed.
Yet it shouldn't block the first include above since that macro isn't defined,
which is what the error suggests since it doesn't have strstr()
If _LINUX_STRING_H is defined, strstr() should be available.

Investigating this issue, it only happens when CONFIG_DYNAMIC_DEBUG is not
set and line 170 of dynamic_debug.h runs, but just above we have an
include of string.h.

Very strange that #include <linux/string.h> isn't doing its job.

The first thing I tried is to understand where dynamic_debug.h is used and
removed the unneeded ones:
--------------------------------------------------------------------------
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -11,7 +11,6 @@
 #include <linux/log2.h>
 #include <linux/typecheck.h>
 #include <linux/printk.h>
-#include <linux/dynamic_debug.h>
 #include <asm/byteorder.h>
 #include <uapi/linux/kernel.h>

diff --git a/include/linux/printk.h b/include/linux/printk.h
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -307,10 +307,11 @@ asmlinkage __printf(1, 2) __cold void __pr_info(const char *fmt, ...);
        no_printk(KERN_DEBUG pr_fmt(fmt), ##__VA_ARGS__)
 #endif

-#include <linux/dynamic_debug.h>

 /* If you are writing a driver, please use dev_dbg instead */
 #if defined(CONFIG_DYNAMIC_DEBUG)
+#include <linux/dynamic_debug.h>
+
 /* dynamic_pr_debug() uses pr_fmt() internally so we don't need it here */
 #define pr_debug(fmt, ...) \
        dynamic_pr_debug(fmt, ##__VA_ARGS__)
diff --git a/kernel/module.c b/kernel/module.c
index beaebea..e70a2fa 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -60,6 +60,7 @@
 #include <linux/jump_label.h>
 #include <linux/pfn.h>
 #include <linux/bsearch.h>
+#include <linux/dynamic_debug.h>
 #include <uapi/linux/module.h>
 #include "module-internal.h"
--------------------------------------------------------------------------

This diff [0] fixes the issue but it is a workaround for the original
issue about string.h not being properly included in dynamic_debug.h

Puzzled by this and can't figure out what is happening wrong.

The second thing I tried was adding
#warning "Linking to string header"
in include/linux/string.h, and I don't see any include path mentioning
kernel.h, where do you see the circular dependency? I might be missing
something.

Thanks,
Luis



[0] Sent for comments:
https://lkml.org/lkml/2016/7/13/686

>>>> +/**
>>>> + * strcpytolower - Copy string and convert to lowercase.
>>>> + * @dst: The buffer to store the result.
>>>> + * @src: The string to convert to lowercase.
>>>> + */
>>>> +static inline void strcpytolower(char *dst, const char *src)
>>>> +{
>>>> +     strlcpytolower(dst, src, -1);
>>>> +}
>>>> +
>>>
>>> Same here, and the 2 below :)
>>>
>>> Thanks Markus,
>>> Luis
>>>
>>>> +/**
>>>> + * strtoupper - Convert string to uppercase.
>>>> + * @s: The string to operate on.
>>>> + */
>>>> +static inline void strtoupper(char *s)
>>>> +{
>>>> +     strlcpytoupper(s, s, -1);
>>>> +}
>>>> +
>>>> +/**
>>>> + * strtolower - Convert string to lowercase.
>>>> + * @s: The string to operate on.
>>>> + */
>>>> +static inline void strtolower(char *s)
>>>> +{
>>>> +     strlcpytolower(s, s, -1);
>>>> +}
>>>> +
>>>>  #endif /* _LINUX_STRING_H_ */
>>>> diff --git a/lib/string.c b/lib/string.c
>>>> index ed83562..fd8c427 100644
>>>> --- a/lib/string.c
>>>> +++ b/lib/string.c
>>>> @@ -952,3 +952,41 @@ char *strreplace(char *s, char old, char new)
>>>>       return s;
>>>>  }
>>>>  EXPORT_SYMBOL(strreplace);
>>>> +
>>>> +/**
>>>> + * strlcpytoupper - Copy a length-limited string and convert to uppercase.
>>>> + * @dst: The buffer to store the result.
>>>> + * @src: The string to convert to uppercase.
>>>> + * @len: Maximum string length. May be SIZE_MAX (-1) to set no limit.
>>>> + */
>>>> +void strlcpytoupper(char *dst, const char *src, size_t len)
>>>> +{
>>>> +     size_t i;
>>>> +
>>>> +     if (!len)
>>>> +             return;
>>>> +
>>>> +     for (i = 0; i < len && src[i]; ++i)
>>>> +             dst[i] = toupper(src[i]);
>>>> +     dst[i < len ? i : i - 1] = '\0';
>>>> +}
>>>> +EXPORT_SYMBOL(strlcpytoupper);
>>>> +
>>>> +/**
>>>> + * strlcpytolower - Copy a length-limited string and convert to lowercase.
>>>> + * @dst: The buffer to store the result.
>>>> + * @src: The string to convert to lowercase.
>>>> + * @len: Maximum string length. May be SIZE_MAX (-1) to set no limit.
>>>> + */
>>>> +void strlcpytolower(char *dst, const char *src, size_t len)
>>>> +{
>>>> +     size_t i;
>>>> +
>>>> +     if (!len)
>>>> +             return;
>>>> +
>>>> +     for (i = 0; i < len && src[i]; ++i)
>>>> +             dst[i] = tolower(src[i]);
>>>> +     dst[i < len ? i : i - 1] = '\0';
>>>> +}
>>>> +EXPORT_SYMBOL(strlcpytolower);
>>>>
>>>

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