On 18/01/2022 02:27, xuyang2018.jy--- via Libc-alpha wrote: > on 2022/1/18 11:56, Theodore Ts'o wrote: >> On Tue, Jan 18, 2022 at 02:43:26AM +0000, xuyang2018.jy@xxxxxxxxxxx wrote: >>>> You're right of course, but out of curiosity, which C library are you >>>> using? >>> I use glibc-2.34. >> >> Hmm, ok. I'm using glibc 2.31, and in this particular program, errno >> shouldn't have been set by any prior system call. I'm guessing maybe >> it was something in crt0 which ended up setting errno? > It maybe a glibc bug. > I cc glibc mailing list and see whether they have met this problem. > > @Florian > > Now, I use glibc-2.34 and run the following program[1] but the errno is > not 0 in the beginning. So is this a known bug on glibc-2.34(Theodore > doesn't meet this problem on glicb-2.31)? > > [1]https://git.kernel.org/pub/scm/fs/xfs/xfstests-dev.git/tree/src/ext4_resize.c The errno should be only set on a failure, no function shall set errno to 0 (it is a POSIX definition which glibc adheres). The application need to explicitly set errno to 0 before the function call to check if an error occurs. So you need to do: errno = 0 new_size = strtoull(argv[2], &tmp, 10); if ((errno) || (*tmp != '\0')) { ... }
