Re: set_labels_identifiers_target -fsanitize=undefined error

[Gavin Smith]

On Sat, Nov 04, 2023 at 01:10:47PM +0000, Sam James wrote:
> 
> John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de> writes:
> 
> > Hi Gavin!
> >
> > On Sat, 2023-11-04 at 11:00 +0000, Gavin Smith wrote:
> >> The line in question is:
> >> 
> >>   memcpy (targets, list_of_labels, labels_number * sizeof(LABEL));
> >> 
> >> - again, the second argument of memcpy.
> >> 
> >> However, main/targets.c was only introduced after Texinfo 7.1 so
> >> this is not the original problem.
> >
> > I'll provide a backtrace as well as the commit that introduced the 
> > regression
> > on SPARC within the next days. Need to set up two new SPARC servers next 
> > week
> > first.
> >
> 
> OK, I tried this out on sparc with Gavin's fix on master, and got...
> 
> export UBSAN_OPTIONS=print_stacktrace=1:halt_on_error=1
> ./autogen.sh;  ./configure PERL_EXT_CFLAGS="-O2 -ggdb3
> -fsanitize=undefined" CFLAGS="-O2 -ggdb3 -fsanitize=undefined"   ; make
> -j$(nproc) ; make check -j$(nproc)
> 
> parsetexi/tree.c:77:11: runtime error: member access within misaligned 
> address 0x0100010e9744 for type 'struct ELEMENT', which requires 8 byte 
> alignment
> 0x0100010e9744: note: pointer points here
>   00 00 01 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  
> 00 00 00 00 00 00 00 00
>               ^
>     #0 0xfff8000102fc12ec in new_element parsetexi/tree.c:77

It is probably a problem with the obstack allocation method that was being
used for ELEMENT (an attempted optimisation, although it's questionable how
successful it was).

According to the glibc manual,

  Each obstack has an “alignment boundary”; each object allocated in the
  obstack automatically starts on an address that is a multiple of the
  specified boundary.  By default, this boundary is aligned so that the
  object can hold any type of data.

(Info node (libc)Obstacks Data Alignment.)

However, we also use the gnulib obstacks module.  Between glibc and gnulib,
it was evidently not meeting this promise.

You can try to set the alignment explicitly:

diff tree.c.old tree.c -u
--- tree.c.old  2023-11-04 16:15:13.632755680 +0000
+++ tree.c      2023-11-04 16:16:36.211072521 +0000
@@ -43,7 +43,10 @@
   if (obs_element_first)
     obstack_free (&obs_element, obs_element_first);
   else
-    obstack_init (&obs_element);
+    {
+      obstack_alignment_mask (&obs_element) = 7; /* 8-byte alignment */
+      obstack_init (&obs_element);
+    }
 
   obs_element_first = obstack_alloc (&obs_element, sizeof (int));


Can you check if that works?