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lib: os: cbprintf: correct arg extraction of wide characters

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The l length modifier can apply to the c format specifier; in that
case the expected value is of type wint_t.  Minimal libc doesn't
define wint_t, and it is complex to do so correctly (must add
<wchar.h>, and use a lot of conditional tricks).

wint_t can differ from wchar_t in rank when wchar_t undergoes default
integral promotion, which it does on xtensa (wchar_t is unsigned
short).  So we can use wchar_t as an approximation, except in va_arg
where we need to use a wider type: int covers this case.

Note that we still don't format wide characters, but we do want to
consume the correct amount of data for a default-promoted extended
character.

Signed-off-by: Peter Bigot <peter.bigot@nordicsemi.no>
This commit is contained in:
Peter Bigot 2021-01-06 11:24:39 -06:00 • committed by Carles Cufí
commit 6297c667c5
1 changed files with 46 additions and 3 deletions
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49
lib/os/cbprintf_complete.c
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@ -88,6 +88,37 @@ enum specifier_cat_enum {
#define CASE_UINT_CHAR case 'c':
#endif
/* We need two pieces of information about wchar_t:
* * WCHAR_IS_SIGNED: whether it's signed or unsigned;
* * WINT_TYPE: the type to use when extracting it from va_args
*
* The former can be determined from the value of WCHAR_MIN if it's defined.
* It's not for minimal libc, so treat it as whatever char is.
*
* The latter should be wint_t, but minimal libc doesn't provide it. We can
* substitute wchar_t as long as that type does not undergo default integral
* promotion as an argument. But it does for at least one toolchain (xtensa),
* and where it does we need to use the promoted type in va_arg() to avoid
* build errors, otherwise we can use the base type. We can tell that
* integral promotion occurs if WCHAR_MAX is strictly less than INT_MAX.
*/
#ifndef WCHAR_MIN
#define WCHAR_IS_SIGNED CHAR_IS_SIGNED
#if WCHAR_IS_SIGNED
#define WINT_TYPE int
#else /* wchar signed */
#define WINT_TYPE unsigned int
#endif /* wchar signed */
#else /* WCHAR_MIN defined */
#define WCHAR_IS_SIGNED ((WCHAR_MIN - 0) != 0)
#if WCHAR_MAX < INT_MAX
/* Signed or unsigned, it'll be int */
#define WINT_TYPE int
#else /* wchar rank vs int */
#define WINT_TYPE wchar_t
#endif /* wchar rank vs int */
#endif /* WCHAR_MIN defined */
/* Case label to identify conversions for signed integral values. The
* corresponding argument_value tag is sint and category is
* SPECIFIER_SINT.
@ -499,7 +530,7 @@ int_conv:
}
/* For c LENGTH_NONE and LENGTH_L would be ok,
* but we don't support wide characters.
* but we don't support formatting wide characters.
*/
if (conv->specifier == 'c') {
unsupported = (conv->length_mod != LENGTH_NONE);
@ -1420,7 +1451,13 @@ int cbvprintf(cbprintf_cb out, void *ctx, const char *fp, va_list ap)
value->sint = va_arg(ap, int);
break;
case LENGTH_L:
value->sint = va_arg(ap, long);
if (WCHAR_IS_SIGNED
&& (conv->specifier == 'c')) {
value->sint = (wchar_t)va_arg(ap,
WINT_TYPE);
} else {
value->sint = va_arg(ap, long);
}
break;
case LENGTH_LL:
value->sint =
@ -1457,7 +1494,13 @@ int cbvprintf(cbprintf_cb out, void *ctx, const char *fp, va_list ap)
value->uint = va_arg(ap, unsigned int);
break;
case LENGTH_L:
value->uint = va_arg(ap, unsigned long);
if ((!WCHAR_IS_SIGNED)
&& (conv->specifier == 'c')) {
value->uint = (wchar_t)va_arg(ap,
WINT_TYPE);
} else {
value->uint = va_arg(ap, unsigned long);
}
break;
case LENGTH_LL:
value->uint =