What's wrong with this code?
bonomi at mail.r-bonomi.com
Tue Dec 13 06:36:39 UTC 2011
From: "John Levine" <johnl at iecc.com> wrote:
> This tiny routine is in a .so loadable module I use. (It's part of the
> mailfront SMTP daemon.)
> static const char* date_string(void)
> static char datebuf;
> time_t now = time(0);
> struct tm* tm = gmtime(&now);
> strftime(datebuf, sizeof datebuf - 1, "%d %b %Y %H:%M:%S -0000", tm);
> return datebuf;
> I was getting bogus dates. Running it under GDB, time() is returning
> -1, and setting errno to 22, which is EINVAL. Changing the call to
> time to time(NULL) or time(&now) made no difference.
> I changed it to a call to gettimeofday(), which works fine. But what
> could the problem have been? When I splice this routine into a tiny
> test program that calls it and prints out the result, it works fine.
how about a tiny .so that includes -only- that routine, and a 3-line or so
main() that links against -that- .so?
> The obvious problem, since it's in a .so, is that it's linking to something
> other than the system library time() function, but I did an nm on the .so,
> and it said this, which sure looks like the system time() function to me:
> U time@@FBSD_1.0
> Setting a breakpoint in gdb gets a complaint about trying to set a
> breakpoint in /lib/libc.so.7.
> Any ideas what the problem was?
The errorno value you report is *NOT* a defined return code for date(3).
The libc date(3) will return only EFAULT, or EPERM, per the manpage.
This lends credence to the possibility of a run-time linker issue.
HOWEVER, there is also the possiblity of memory getting trashed -- in just
the 'right' wrong way -- *elsewhere* in the code. OR a corrupted .so
Mentioning O/S release level, and CPU architecture would be a good idea :)
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