int printf_handler(const char *format, va_list args)
{
    ...
    sv_vsetpvf(printf_str, format, &args);
    ...

##</code><code>##

int printf_handler(const char *format, va_list* args)
{
    ...
    sv_vsetpvf(printf_str, format, args);
    ...

##</code><code>##

#include <stdarg.h>
#include <stdio.h>
#include <errno.h>

void vatest__(char* format, va_list* args) {
    // this kind of represents sv_vsetpvf()
    
    char buf[1024];
    vsprintf(buf, format, *args);
    errno = 0;  // "Success"
    perror(buf);
}

void vatest_(char* format, va_list args) {
    // this represents your printf_handler()
    
    vatest__(format, &args);
}

void vatest(char* format, ...) {
    
    va_list args;
    va_start (args, format);
    vatest_(format, args);
    va_end (args);
}

int main (int argc, char *argv[]) {
    char* msg1 = "foo";
    char* msg2 = "bar";
    vatest("%s: %s",    argv[0], msg1);        // two args
    vatest("%s: %s,%s", argv[0], msg1, msg2);  // three args
    return 0;
}

##</code><code>##

$ gcc -Wall vatest.c -o vatest
vatest.c: In function `vatest_':
vatest.c:17: warning: passing arg 2 of `vatest__' from incompatible pointer type
$ ./vatest
Segmentation fault
$ file vatest
vatest: ELF 64-bit LSB executable, AMD x86-64, version 1 (SYSV), for GNU/Linux 2.6.4, dynamically linked (uses shared libs), for GNU/Linux 2.6.4, not stripped

##</code><code>##

...
void vatest_(char* format, va_list* args) {
    
    vatest__(format, args);
}

void vatest(char* format, ...) {
    
    va_list args;
    va_start (args, format);
    vatest_(format, &args);
    va_end (args);
}
...

##</code><code>##

$ gcc -Wall vatest.c -o vatest
$ ./vatest
./vatest: foo: Success
./vatest: foo,bar: Success