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[klibc] fix: rt_sprintf() writes nothing when libc vsnprintf is used #11953

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[klibc] fix: rt_sprintf() writes nothing when libc vsnprintf is used #11953

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11 changes: 11 additions & 0 deletions src/klibc/kstdio.c
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Original file line number Diff line number Diff line change
Expand Up @@ -51,7 +51,18 @@ RTM_EXPORT(rt_snprintf);
*/
int rt_vsprintf(char *buf, const char *format, va_list arg_ptr)
{
#ifdef RT_KLIBC_USING_LIBC_VSNPRINTF
/*
* rt_vsnprintf() delegates to libc here. Passing (size_t)-1 to it is not
* safe: libc computes the end of the buffer as buf + size, which overflows
* on 64-bit targets, and the call then fails without writing anything
* (rt_sprintf() returned -1 and left the buffer untouched). libc has
* vsprintf() for exactly this case.
*/
return vsprintf(buf, format, arg_ptr);
#else
return rt_vsnprintf(buf, (size_t) - 1, format, arg_ptr);
#endif
}
RTM_EXPORT(rt_vsprintf);

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