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This is GCC plugin, made to eliminate cost for parsing printf-like format strings in runtime by doing this at compile time.It uses GCC plugin API to walk through gimple tree, get format-string value and insert calls to specifiedto plugin functions instead of printf-alike. Note:this can be done only to constant format-stringparameters.

So, the idea is to change the function calls like this:

print_on_level(LOG_DEBUG, "cwd:%x swd:%x twd:%x fop:%x mxcsr:%x mxcsr_mask:%x\n",                (int)i387->cwd, (int)i387->swd, (int)i387->twd,                (int)i387->fop, (int)i387->mxcsr, (int)i387->mxcsr_mask);

To sequence of calls like:

print_str_level(LOG_DEBUG, "cwd:");print_int_level(LOG_DEBUG, (int)i387->cwd);print_str_level(LOG_DEBUG, " swd:");print_int_level(LOG_DEBUG, (int)i387->swd);print_str_level(LOG_DEBUG, " twd:");print_int_level(LOG_DEBUG, (int)i387->twd);print_str_level(LOG_DEBUG, " fop:");print_int_level(LOG_DEBUG, (int)i387->fop);print_str_level(LOG_DEBUG, " mxcsr:");print_int_level(LOG_DEBUG, (int)i387->mxcsr);print_str_level(LOG_DEBUG, " mxcsr_mask:");print_int_level(LOG_DEBUG, (int)i387->mxcsr_mask);print_str_level(LOG_DEBUG, "\n");

This will speed up the runtime by eliminating needless parsing of format string.All is done by GCC plugin during compilation.One should specify printf-alike functionprint_on_level andprint_str_level,print_int_levelas a plugin parameters.

To use this GCC compiler plugin, you need compile it with:

make

Then change your makefile so GCC will use plugin like this:

%.o: %.c    gcc -o $@ $< -fplugin=./cprintf.so -fplugin-arg-cprintf-printf="printf(0): %c putchar %s putstring  \                            %d putint %f putfloat %m puterrstr"

Whereprintf(0) means that format string is the first parameter.If you provide function likefprintf(1) which has some (one) parameters before format string,they will be passed to handlers in the same order.

Handlers:putchar function for%c specifier and so on.Note, specifier may be any length, ending with space symbol. I.e.,%h$up is a valid specifierh$up.

For some user-defined functionfoo(arg1, arg2, const char *fmt, ...) cprintfplugin expects that following specifiers have their special meaning ifhandler-functions have been specified in plugin args:

• %s is for strings (const char*). Cprintf will use it to output parts offormat string between specifiers; Function prototype in example:bar(arg1, arg2, const char *str);
• %c is for chars (const char). Cprintf will use it to output single charsfrom format string; Function prototype in example:baz(arg1, arg2, const char s);
• %% special meaning for raw string output; Function prototype in example:quux(arg1, arg2, void *ptr, size_t size, size_t nmemb);

Tip: consider using%% specifier asfwrite() function as it willgive great performance enhance.