A long time ago Junio added this line to always ensure that the output array created by remove_duplicates() had a NULL as its terminating node. Today none of the downstream consumers of this array care about a NULL terminator; they only pay attention to the size of the array (as indicated by nr_heads). In (nearly?) all cases passing a NULL element will cause SIGSEGV failures. So this NULL terminal is not actually necessary.
Unfortunately we cannot continue to NULL terminate the array at this point as the array may only have been allocated large enough to match the input of nr_heads. If there are no duplicates than we would be trying to store NULL into heads[nr_heads] and that may be outside of the array.
My recent series to cleanup builtin-fetch changed the allocation of the heads array from 256 entries to exactly nr_heads thus ensuring we were always overstepping the array and causing memory corruption.
Signed-off-by: Shawn Pearce <spearce@blink.home.spearce.org> ---
This patch is meant for the top of the db/fetch-pack series (currently in pu) but it may actually need to be applied back on prior versions (e.g. maint). The code affected seems to predate builtin-fetch by quite a bit and we may just be getting lucky that the array is always allocated large enough for this extra entry.
It almost fixes the corruption Junio saw in t3200. When combined with the next patch (2/2) that corruption appears to be fixed on both my Mac OS X and my Linux amd64 system.
builtin-fetch-pack.c | 1 - 1 files changed, 0 insertions(+), 1 deletions(-)
Show changes to builtin-fetch-pack.c +0 −1
diff --git a/builtin-fetch-pack.c b/builtin-fetch-pack.c index b0936cc..2977a94 100644 --- a/builtin-fetch-pack.c +++ b/builtin-fetch-pack.c @@ -654,7 +654,6 @@ static int remove_duplicates(int nr_heads, char **heads) heads[dst] = heads[src]; dst++; } - heads[dst] = 0; return dst; }
-- 1.5.3.1.921.g8c3b