Date: Fri, 7 Apr 2017 14:35:20 +0000 From: Pascal Cuoq <cuoq@...st-in-soft.com> To: "musl@...ts.openwall.com" <musl@...ts.openwall.com> Subject: Re: Undefined behavior in sprintf(dest, "%lld", -1LL) > On 07 Apr 2017, at 16:26, Rich Felker <dalias@...c.org> wrote: > > On Fri, Apr 07, 2017 at 02:22:46PM +0000, Pascal Cuoq wrote: >> I am running musl's implementation inside tis-interpreter, a C interpreter that detects a very wide palette of undefined behaviors. >> >> ... >> >> On the basis of this result, I would tentatively offer that the undefined behavior that tis-interpreter warns about is real and is caused by line 55 in vfprintf.c: >> >> #define LLONG ULLONG >> >> Because of this approach, when LLONG is passed to the function pop_arg(), the switch case at line 141 is taken: >> >> break; case ULLONG: arg->i = va_arg(*ap, unsigned long long); >> >> This causes UB by consuming a (negative) long long argument from a va_list with va_arg(..., unsigned long long). > > Does defining the ODD_TYPES macro fix the problem? My leaning is to > just remove that #ifdef logic and always use the correct type with > va_arg. All that was doing was saving a few bytes of code; the change > should not affect performance. Yes, this fixes it. I had to add the following line to vfprintf.c: #include <stddef.h> because the type ptrdiff_t is used at line 151 in this variation of the code. Thanks!
Powered by blists - more mailing lists
Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.