https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68737
--- Comment #13 from dave.anglin at bell dot net --- On 2018-09-04 9:48 AM, redi at gcc dot gnu.org wrote: > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68737 > > --- Comment #12 from Jonathan Wakely <redi at gcc dot gnu.org> --- > (In reply to dave.anglin from comment #11) >> JAGaf47646: with small buffer vsnprintf always returns -1 > Aha, that is probably it. We pass 0 as the size, which is supposed to make > vsnprintf tell you how many bytes it would have written (as that's how we find > out the required length). > > It's curious that it printed "returned 4, errno = 0" when you tested it > though. > Maybe GCC optimized the call and didn't use the OS function. > > Does it return -1 if you use -fno-builtin-vsnprintf ? No. I checked .s file and GCC isn't optimizing the call. It returns -1 when passed a nonzero size that is too small. Passing 4 causes it to return -1: using vsnprintf returned -1, errno = 0 Passing 5 is okay: using vsnprintf returned 4, errno = 0 Maybe it's returning an incorrect length when passed 0 in some locales? Dave
