disabling sha1dc unaligned access, was Re: One failed self test on Fedora 29

[Jeff King <peff@peff.net>]

On Mon, Mar 11, 2019 at 11:00:25AM +0900, Junio C Hamano wrote:

> Jeffrey Walton <noloader@gmail.com> writes:
> 
> > I think this is the patch for sha1dc/sha1.c . It stops using unaligned
> > accesses by default, but still honors SHA1DC_FORCE_UNALIGNED_ACCESS
> > for those who want it. Folks who want the undefined behavior have to
> > do something special.
> 
> Hmph, I somehow thought that folks who want to stick to the
> standard printed on paper penalizing what practicaly works well in
> the real world would be the one doing extra things.

Unfortunately, I don't think sha1dc currently supports #defines in that
direction. The only logic is "if we are on intel, do unaligned loads"
and "even if we are not on intel, do it anyway". There is no "even if we
are on intel, do not do unaligned loads".

I think you'd need something like this:

diff --git a/Makefile b/Makefile
index 148668368b..705c54dcd8 100644
--- a/Makefile
+++ b/Makefile
@@ -1194,6 +1194,7 @@ BASIC_CFLAGS += -fsanitize=$(SANITIZE) -fno-sanitize-recover=$(SANITIZE)
 BASIC_CFLAGS += -fno-omit-frame-pointer
 ifneq ($(filter undefined,$(SANITIZERS)),)
 BASIC_CFLAGS += -DNO_UNALIGNED_LOADS
+BASIC_CFLAGS += -DSHA1DC_DISALLOW_UNALIGNED_ACCESS
 endif
 ifneq ($(filter leak,$(SANITIZERS)),)
 BASIC_CFLAGS += -DSUPPRESS_ANNOTATED_LEAKS
diff --git a/sha1dc/sha1.c b/sha1dc/sha1.c
index df0630bc6d..0bdf80d778 100644
--- a/sha1dc/sha1.c
+++ b/sha1dc/sha1.c
@@ -124,9 +124,11 @@
 #endif
 /*ENDIANNESS SELECTION*/
 
+#ifndef SHA1DC_DISALLOW_UNALIGNED_ACCESS
 #if defined(SHA1DC_FORCE_UNALIGNED_ACCESS) || defined(SHA1DC_ON_INTEL_LIKE_PROCESSOR)
 #define SHA1DC_ALLOW_UNALIGNED_ACCESS
 #endif /*UNALIGNMENT DETECTION*/
+#endif
 
 
 #define rotate_right(x,n) (((x)>>(n))|((x)<<(32-(n))))

but of course we cannot touch sha1dc/*, because we might actually be
using the submodule copy instead. And AFAIK there is no good way to
modify the submodule-provided content as part of the build. Why do we
even have the submodule again? ;P

I guess the same would be true for DC_SHA1_EXTERNAL, too, though.

So anyway, I think this needs a patch to the upstream sha1dc project.

-Peff