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SubjectRe: [PATCH] twist: allow converting pr_devel()/pr_debug() into printk(KERN_DEBUG)
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On 2020/05/28 0:55, Petr Mladek wrote:
>>> Well, it would be possible to call vsprintf() with NULL buffer. It is
>>> normally used to calculate the length of the message before it is
>>> printed. But it also does all the accesses without printing anything.
>>
>> OK. I think that redirecting pr_debug() to vsnprintf(NULL, 0) will be
>> better than modifying dynamic_debug path, for
>
> It might get more complicated if you would actually want to see
> pr_debug() messages for a selected module in the fuzzer.

I don't expect that automated testing can afford selectively enabling
DYNAMIC_DEBUG_BRANCH(id) conditions. But we could evaluate all arguments
by calling snprintf(NULL, 0) if the condition to call printk() is false.

> vsprintf(NULL, ) can be called for pr_debug() messages in
> vprintk_store(). It will be again only a single place for
> all printk() wrappers.

I couldn't catch what you mean. The problem of pr_debug() is that
vprintk_store() might not be called because of

#define no_printk(fmt, ...) \
({ \
if (0) \
printk(fmt, ##__VA_ARGS__); \
0; \
})

#define pr_debug(fmt, ...) \
no_printk(KERN_DEBUG pr_fmt(fmt), ##__VA_ARGS__)

or

#define __dynamic_func_call(id, fmt, func, ...) do { \
DEFINE_DYNAMIC_DEBUG_METADATA(id, fmt); \
if (DYNAMIC_DEBUG_BRANCH(id)) \
func(&id, ##__VA_ARGS__); \
} while (0)

#define _dynamic_func_call(fmt, func, ...) \
__dynamic_func_call(__UNIQUE_ID(ddebug), fmt, func, ##__VA_ARGS__)

#define dynamic_pr_debug(fmt, ...) \
_dynamic_func_call(fmt, __dynamic_pr_debug, \
pr_fmt(fmt), ##__VA_ARGS__)

#define pr_debug(fmt, ...) \
dynamic_pr_debug(fmt, ##__VA_ARGS__)

. Maybe we can append

else if (IS_BUILTIN(CONFIG_TWIST_ALWAYS_EVALUATE_DEBUG_PRINTK)) \
snprintf(NULL, 0, fmt, ##__VA_ARGS__); \

to no_printk() and __dynamic_func_call().

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