[committed] Fix assertion 'off == cu_size' in recompute_abbrevs

[committed] Fix assertion 'off == cu_size' in recompute_abbrevs

[Tom de Vries]

Hi,

With an executable from PR25024, we manage to reproduce PR24764:
...
$ dwz -l0 clang-offload-bundler-10.0.0-0.20190817snap5.fc30.x86_64.debug
dwz: dwz.c:9920: recompute_abbrevs: Assertion `off == cu_size' failed.
Aborted (core dumped)
...

The problem is that the cu_size as computed during recompute_abbrevs is not
the same as was computed before during compute_abbrevs.

I tracked down the first DIE in the CU that has a different size, at 0xdf615:
...
 <5><df615>: Abbrev Number: 65 (DW_TAG_formal_parameter)
    <df616>   DW_AT_type        : <0xe33be>
    <df618>   DW_AT_artificial  : 1
...

Using a debug patch, we can track the size of the DIE during compute_abbrevs:
...
init_new_die_offsets: intracusize: 2
init_new_die_offsets: start die_size: 0
init_new_die_offsets: add DIE code size to die_size: 1
init_new_die_offsets: add nr_refs * intracusize to die_size: 3
update_new_die_offsets: die_size: 3
update_new_die_offsets: die_size: 3
finalize_new_die_offsets: die_size: 3
...
and recompute_abbrevs:
...
init_new_die_offsets: intracusize: 3
init_new_die_offsets: start die_size: 0
init_new_die_offsets: add DIE code size to die_size: 1
init_new_die_offsets: add nr_refs * intracusize to die_size: 4
update_new_die_offsets: die_size: 4
update_new_die_offsets: die_size: 4
update_new_die_offsets: die_size: 4
finalize_new_die_offsets: die_size: 4
...

The difference starts in init_new_die_offsets, when adding intracusize, which
is different for compute_abbrevs and recompute_abbrevs (2 vs. 3).

The code in recompute_abbrevs that calculates intracusize for the relevant
init_new_die_offsets call is:
...
      /* Need to be conservatively high estimate, as update_new_die_offsets
        relies on the offsets always decreasing.  cu_size at this point is
        the size we will end up with in the end, but if cu_size is
        sufficiently close (from bottom) to some uleb128 boundary (say
        16384), init_new_die_offsets might return off above that boundary
        and then update_new_die_offsets might fail its assertions on
        reference to DIEs that crossed the uleb128 boundary.  */
      intracusize = size_of_uleb128 (2 * cu_size);

      off = init_new_die_offsets (cu->cu_die, headersz, intracusize);
...
where the '2 * cu_size' is the result of commit d16aa5e "Fix up
recompute_abbrevs if cu_size is close below an uleb128 boundary and
init_new_die_offsets would return offset above that uleb128 boundary":
...
-      intracusize = size_of_uleb128 (cu_size);
+      intracusize = size_of_uleb128 (2 * cu_size);
...

Reverting commit d16aa5e gets us an intracusize of 2 in recompute_abbrevs, and
fixes the assert.  However, doing so reintroduces the assertion that was fixed
by the commit (at least, provided commit a4668e1 "Fix assertion failure in
create_import_tree" is also reverted):
...
$ dwz -l0 inkview.debug
dwz: dwz.c:8527: update_new_die_offsets: Assertion \
  `die->u.p2.die_intracu_udata_size >= intracu_udata_size' failed.
Aborted (core dumped)
...

Fix the 'off == cu_size' assert (without introducing the regression for
inkview.debug) by:
- saving the intracusize used for the call to init_new_die_offsets in
  compute_abbrevs, and
- reusing the saved intracusize for the call to init_new_die_offsets in
  recompute_abbrevs.

Also tested with clang and CheckerOptionHandlingAnalyzerPlugin.so, for which
this PR also triggered.

Committed to trunk.

Thanks,
- Tom

Fix assertion 'off == cu_size' in recompute_abbrevs

2019-11-27  Tom de Vries  <tdevries@suse.de>

	PR dwz/24764
	* dwz.c (struct dw_cu): Add initial_intracusize field.
	(compute_abbrevs): Initalize initial_intracusize.
	(recompute_abbrevs): Use initial_intracusize.

---
 dwz.c | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/dwz.c b/dwz.c
index 8d62444..36b54d8 100644
--- a/dwz.c
+++ b/dwz.c
@@ -689,6 +689,9 @@ struct dw_cu
   unsigned int cu_chunk;
   /* Form chosen for intra-cu references.  */
   enum dwarf_form cu_intracu_form;
+  /* Intracusize argument to init_new_die_offsets.  Set in compute_abbrevs,
+     used in recompute_abbrevs.  */
+  unsigned int initial_intracusize;
 };
 
 /* Internal representation of a debugging information entry (DIE).
@@ -8737,6 +8740,7 @@ compute_abbrevs (DSO *dso)
 	  intracusize = i;
 	}
       while (1);
+      cu->initial_intracusize = intracusize;
       off = init_new_die_offsets (cu->cu_die, headersz, intracusize);
       do
 	{
@@ -9889,14 +9893,7 @@ recompute_abbrevs (dw_cu_ref cu, unsigned int cu_size)
     }
   else
     {
-      /* Need to be conservatively high estimate, as update_new_die_offsets
-	 relies on the offsets always decreasing.  cu_size at this point is
-	 the size we will end up with in the end, but if cu_size is
-	 sufficiently close (from bottom) to some uleb128 boundary (say
-	 16384), init_new_die_offsets might return off above that boundary
-	 and then update_new_die_offsets might fail its assertions on
-	 reference to DIEs that crossed the uleb128 boundary.  */
-      intracusize = size_of_uleb128 (2 * cu_size);
+      intracusize = cu->initial_intracusize;
 
       off = init_new_die_offsets (cu->cu_die, headersz, intracusize);
       do