[kvm-unit-tests PATCH v3 12/27] lib/printf: Support for precision modifier in printf

Nikos Nikoleris
2022-06-30T10:04:09Z

This follows the typical format of:

printf("%.Ns", *str);

Where N might be a decimal digit string or '*'. This feature is used
by a future change.

See also: man 3 printf

Signed-off-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Andrew Jones <drjones@redhat.com>
---
lib/printf.c | 95 ++++++++++++++++++++++++++++++++++++++++++----------
1 file changed, 78 insertions(+), 17 deletions(-)

diff --git a/lib/printf.c b/lib/printf.c
index 383799e..d600199 100644
--- a/lib/printf.c
+++ b/lib/printf.c
@@ -6,6 +6,7 @@
*/

#include "libcflat.h"
+#include "ctype.h"

#define BUFSZ 2000

@@ -19,6 +20,7 @@ typedef struct strprops {
char pad;
int npad;
bool alternate;
+ int precision;
} strprops_t;

static void addchar(pstream_t *p, char c)
@@ -43,7 +45,7 @@ static void print_str(pstream_t *p, const char *s, strprops_t props)
}
}

- while (*s)
+ while (*s && props.precision--)
addchar(p, *s++);

if (npad < 0) {
@@ -73,12 +75,13 @@ static void print_int(pstream_t *ps, long long n, int base, strprops_t props)
n /= base;
}

+ while (p == buf || (p - buf < props.precision))
+ *p++ = '0';
+ props.precision = -1;
+
if (s)
*p++ = '-';

- if (p == buf)
- *p++ = '0';
-
for (i = 0; i < (p - buf) / 2; ++i) {
char tmp;

@@ -104,8 +107,13 @@ static void print_unsigned(pstream_t *ps, unsigned long long n, int base,
}

if (p == buf)
+ props.alternate = false;
+
+ while (p == buf || (p - buf < props.precision))
*p++ = '0';
- else if (props.alternate && base == 16) {
+ props.precision = -1;
+
+ if (props.alternate && base == 16) {
if (props.pad == '0') {
addchar(ps, '0');
addchar(ps, 'x');
@@ -147,9 +155,56 @@ static int fmtnum(const char **fmt)
return num;
}

+/*
+ * Adapted from drivers/firmware/efi/libstub/vsprintf.c
+ */
+static int skip_atoi(const char **s)
+{
+ int i = 0;
+
+ do {
+ i = i*10 + *((*s)++) - '0';
+ } while (isdigit(**s));
+
+ return i;
+}
+
+/*
+ * Adapted from drivers/firmware/efi/libstub/vsprintf.c
+ */
+static int get_int(const char **fmt, va_list *ap)
+{
+ if (isdigit(**fmt))
+ return skip_atoi(fmt);
+
+ if (**fmt == '*') {
+ ++(*fmt);
+ /* it's the next argument */
+ return va_arg(*ap, int);
+ }
+ return 0;
+}
+
int vsnprintf(char *buf, int size, const char *fmt, va_list va)
{
pstream_t s;
+ 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, va);

s.buffer = buf;
s.remain = size - 1;
@@ -160,6 +215,7 @@ int vsnprintf(char *buf, int size, const char *fmt, va_list va)
strprops_t props;
memset(&props, 0, sizeof(props));
props.pad = ' ';
+ props.precision = -1;

if (f != '%') {
addchar(&s, f);
@@ -172,11 +228,15 @@ morefmt:
addchar(&s, '%');
break;
case 'c':
- addchar(&s, va_arg(va, int));
+ addchar(&s, va_arg(args, int));
break;
case '\0':
--fmt;
break;
+ case '.':
+ props.pad = ' ';
+ props.precision = get_int(&fmt, &args);
+ goto morefmt;
case '#':
props.alternate = true;
goto morefmt;
@@ -204,54 +264,55 @@ morefmt:
case 'd':
switch (nlong) {
case 0:
- print_int(&s, va_arg(va, int), 10, props);
+ print_int(&s, va_arg(args, int), 10, props);
break;
case 1:
- print_int(&s, va_arg(va, long), 10, props);
+ print_int(&s, va_arg(args, long), 10, props);
break;
default:
- print_int(&s, va_arg(va, long long), 10, props);
+ print_int(&s, va_arg(args, long long), 10, props);
break;
}
break;
case 'u':
switch (nlong) {
case 0:
- print_unsigned(&s, va_arg(va, unsigned), 10, props);
+ print_unsigned(&s, va_arg(args, unsigned int), 10, props);
break;
case 1:
- print_unsigned(&s, va_arg(va, unsigned long), 10, props);
+ print_unsigned(&s, va_arg(args, unsigned long), 10, props);
break;
default:
- print_unsigned(&s, va_arg(va, unsigned long long), 10, props);
+ print_unsigned(&s, va_arg(args, unsigned long long), 10, props);
break;
}
break;
case 'x':
switch (nlong) {
case 0:
- print_unsigned(&s, va_arg(va, unsigned), 16, props);
+ print_unsigned(&s, va_arg(args, unsigned int), 16, props);
break;
case 1:
- print_unsigned(&s, va_arg(va, unsigned long), 16, props);
+ print_unsigned(&s, va_arg(args, unsigned long), 16, props);
break;
default:
- print_unsigned(&s, va_arg(va, unsigned long long), 16, props);
+ print_unsigned(&s, va_arg(args, unsigned long long), 16, props);
break;
}
break;
case 'p':
props.alternate = true;
- print_unsigned(&s, (unsigned long)va_arg(va, void *), 16, props);
+ print_unsigned(&s, (unsigned long)va_arg(args, void *), 16, props);
break;
case 's':
- print_str(&s, va_arg(va, const char *), props);
+ print_str(&s, va_arg(args, const char *), props);
break;
default:
addchar(&s, f);
break;
}
}
+ va_end(args);
*s.buffer = 0;
return s.added;
}
--
2.25.1