Am 02.10.2017 um 07:08 schrieb Jeff King:

On Sun, Oct 01, 2017 at 04:45:13PM +0200, René Scharfe wrote:

quoted

lookup_blob() etc. can return NULL if the referenced object isn't of the
expected type.  In theory it's wrong to reference the object member in
that case.  In practice it's OK because it's located at offset 0 for all
types, so the pointer arithmetic (NULL + 0) is optimized out by the
compiler.  The issue is reported by Clang's AddressSanitizer, though.

Avoid the ASan error by casting the results of the lookup functions to
struct object pointers.  That works fine with NULL pointers as well.  We
already rely on the object member being first in all object types in
other places in the code.

Out of curiosity, did you have to do anything to coax this out of ASan
(e.g., a specific version)?  I've been running it pretty regularly and
didn't see this one (I did switch from clang to gcc a month or two ago,
but this code is pretty old, I think).

I did "make -j4 SANITIZE=undefined,address BLK_SHA1=1 test" with
clang version 4.0.1-1 (tags/RELEASE_401/final), and t1450-fsck.sh failed.

René