in efi/libstub/vsprintf.c [301:553]
int vsnprintf(char *buf, size_t size, const char *fmt, va_list ap)
{
/* The maximum space required is to print a 64-bit number in octal */
char tmp[(sizeof(unsigned long long) * 8 + 2) / 3];
char *tmp_end = &tmp[ARRAY_SIZE(tmp)];
long long num;
int base;
const char *s;
size_t len, pos;
char sign;
int flags; /* flags to number() */
int field_width; /* width of output field */
int precision; /* min. # of digits for integers; max
number of chars for from string */
int qualifier; /* 'h', 'hh', 'l' or 'll' for integer fields */
va_list args;
/*
* We want to pass our input va_list to helper functions by reference,
* but there's an annoying edge case. If va_list was originally passed
* to us by value, we could just pass &ap down to the helpers. This is
* the case on, for example, X86_32.
* However, on X86_64 (and possibly others), va_list is actually a
* size-1 array containing a structure. Our function parameter ap has
* decayed from T[1] to T*, and &ap has type T** rather than T(*)[1],
* which is what will be expected by a function taking a va_list *
* parameter.
* One standard way to solve this mess is by creating a copy in a local
* variable of type va_list and then passing a pointer to that local
* copy instead, which is what we do here.
*/
va_copy(args, ap);
for (pos = 0; *fmt; ++fmt) {
if (*fmt != '%' || *++fmt == '%') {
PUTC(*fmt);
continue;
}
/* process flags */
flags = get_flags(&fmt);
/* get field width */
field_width = get_int(&fmt, &args);
if (field_width < 0) {
field_width = -field_width;
flags |= LEFT;
}
if (flags & LEFT)
flags &= ~ZEROPAD;
/* get the precision */
precision = -1;
if (*fmt == '.') {
++fmt;
precision = get_int(&fmt, &args);
if (precision >= 0)
flags &= ~ZEROPAD;
}
/* get the conversion qualifier */
qualifier = -1;
if (*fmt == 'h' || *fmt == 'l') {
qualifier = *fmt;
++fmt;
if (qualifier == *fmt) {
qualifier -= 'a'-'A';
++fmt;
}
}
sign = 0;
switch (*fmt) {
case 'c':
flags &= LEFT;
s = tmp;
if (qualifier == 'l') {
((u16 *)tmp)[0] = (u16)va_arg(args, unsigned int);
((u16 *)tmp)[1] = L'\0';
precision = INT_MAX;
goto wstring;
} else {
tmp[0] = (unsigned char)va_arg(args, int);
precision = len = 1;
}
goto output;
case 's':
flags &= LEFT;
if (precision < 0)
precision = INT_MAX;
s = va_arg(args, void *);
if (!s)
s = precision < 6 ? "" : "(null)";
else if (qualifier == 'l') {
wstring:
flags |= WIDE;
precision = len = utf16s_utf8nlen((const u16 *)s, precision);
goto output;
}
precision = len = strnlen(s, precision);
goto output;
/* integer number formats - set up the flags and "break" */
case 'o':
base = 8;
break;
case 'p':
if (precision < 0)
precision = 2 * sizeof(void *);
fallthrough;
case 'x':
flags |= SMALL;
fallthrough;
case 'X':
base = 16;
break;
case 'd':
case 'i':
flags |= SIGN;
fallthrough;
case 'u':
flags &= ~SPECIAL;
base = 10;
break;
default:
/*
* Bail out if the conversion specifier is invalid.
* There's probably a typo in the format string and the
* remaining specifiers are unlikely to match up with
* the arguments.
*/
goto fail;
}
if (*fmt == 'p') {
num = (unsigned long)va_arg(args, void *);
} else {
num = get_number(flags & SIGN, qualifier, &args);
}
sign = get_sign(&num, flags);
if (sign)
--field_width;
s = number(tmp_end, num, base, flags & SMALL);
len = tmp_end - s;
/* default precision is 1 */
if (precision < 0)
precision = 1;
/* precision is minimum number of digits to print */
if (precision < len)
precision = len;
if (flags & SPECIAL) {
/*
* For octal, a leading 0 is printed only if necessary,
* i.e. if it's not already there because of the
* precision.
*/
if (base == 8 && precision == len)
++precision;
/*
* For hexadecimal, the leading 0x is skipped if the
* output is empty, i.e. both the number and the
* precision are 0.
*/
if (base == 16 && precision > 0)
field_width -= 2;
else
flags &= ~SPECIAL;
}
/*
* For zero padding, increase the precision to fill the field
* width.
*/
if ((flags & ZEROPAD) && field_width > precision)
precision = field_width;
output:
/* Calculate the padding necessary */
field_width -= precision;
/* Leading padding with ' ' */
if (!(flags & LEFT))
while (field_width-- > 0)
PUTC(' ');
/* sign */
if (sign)
PUTC(sign);
/* 0x/0X for hexadecimal */
if (flags & SPECIAL) {
PUTC('0');
PUTC( 'X' | (flags & SMALL));
}
/* Zero padding and excess precision */
while (precision-- > len)
PUTC('0');
/* Actual output */
if (flags & WIDE) {
const u16 *ws = (const u16 *)s;
while (len-- > 0) {
u32 c32 = utf16_to_utf32(&ws);
u8 *s8;
size_t clen;
if (c32 < 0x80) {
PUTC(c32);
continue;
}
/* Number of trailing octets */
clen = 1 + (c32 >= 0x800) + (c32 >= 0x10000);
len -= clen;
s8 = (u8 *)&buf[pos];
/* Avoid writing partial character */
PUTC('\0');
pos += clen;
if (pos >= size)
continue;
/* Set high bits of leading octet */
*s8 = (0xf00 >> 1) >> clen;
/* Write trailing octets in reverse order */
for (s8 += clen; clen; --clen, c32 >>= 6)
*s8-- = 0x80 | (c32 & 0x3f);
/* Set low bits of leading octet */
*s8 |= c32;
}
} else {
while (len-- > 0)
PUTC(*s++);
}
/* Trailing padding with ' ' */
while (field_width-- > 0)
PUTC(' ');
}
fail:
va_end(args);
if (size)
buf[min(pos, size-1)] = '\0';
return pos;
}