I've been running a debug build of vim for a while, and while diagnosing a
slowness problem noticed that it was much slower than the version I get with my
distro (Kubuntu 14.04, 7.4.52), so I changed my compiler flags to add -O2 and
recompiled.
The resulting executable aborted instantly:
*** buffer overflow detected ***: vim terminated
and splurges out a backtrace and about 300 lines of memory map.
The version of gcc is 4.8.2.
Getting a core dump, I see that gcc is doing a checked strcpy and aborting.
This occurs at my line 874 of eval.c:
STRCPY(p->vv_di.di_key, p->vv_name);
p is pointing at the first element of vimvars:
static struct vimvar
{
char *vv_name; /* name of variable, without v: */
dictitem_T vv_di; /* value and name for key */
char vv_filler[16]; /* space for LONGEST name below!!! */
char vv_flags; /* VV_COMPAT, VV_RO, VV_RO_SBX */
} vimvars[VV_LEN] =
and vv_di is a
struct dictitem_S
{
typval_T di_tv; /* type and value of the variable */
char_u di_flags; /* flags (only used for variable) */
char_u di_key[1]; /* key (actually longer!) */
}
This is done to avoid a allocation for di_key. I think gcc is complaining that
di_key has only room for one char, and doesn't realize that we've allowed space
in vv_filler for the data.
Why it should do that with -O2 and not without has me wondering, perhaps the
members of struct vimvar are being reordered?
Anyway, if I add -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE=1 to the compile flags
(gcc is using a default of 2) the abort goes away, but this leaves an uneasy
feeling.
I thought having the last char item of a struct being declared as [1] was valid
C, and I have a vague idea that there's an explicit ok for this sort of thing.
Regards, John Little
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