[committed] Fix memory leak in write_multifile

[Tom de Vries <tdevries@suse.de>]

Hi,

When building dwz with -fsanitize=address, we run into some memory leaks:
...
$ cp hello 1; ./dwz 1; cp 1 2; ./dwz -m 3 1 2
./dwz: 1: DWARF compression not beneficial - old size 3372 new size 3372
./dwz: 2: DWARF compression not beneficial - old size 3372 new size 3372

=================================================================
==8024==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 432 byte(s) in 6 object(s) allocated from:
    #0 0x7f7ab92cc6d8 in __interceptor_calloc \
         (/usr/lib64/libasan.so.4+0xdc6d8)
    #1 0x475dc1 in htab_try_create hashtab.c:164
    #2 0x44c610 in build_abbrevs dwz.c:11230
    #3 0x44ee00 in compute_abbrevs dwz.c:11510
    #4 0x46f07c in dwz dwz.c:15396
    #5 0x474e0d in dwz_files_1 dwz.c:16327
    #6 0x475699 in dwz_files dwz.c:16417
    #7 0x4759fc in main dwz.c:16458
    #8 0x7f7ab8c41349 in __libc_start_main (/lib64/libc.so.6+0x24349)

Indirect leak of 2928 byte(s) in 6 object(s) allocated from:
    #0 0x7f7ab92cc6d8 in __interceptor_calloc \
         (/usr/lib64/libasan.so.4+0xdc6d8)
    #1 0x475de7 in htab_try_create hashtab.c:168
    #2 0x44c610 in build_abbrevs dwz.c:11230
    #3 0x44ee00 in compute_abbrevs dwz.c:11510
    #4 0x46f07c in dwz dwz.c:15396
    #5 0x474e0d in dwz_files_1 dwz.c:16327
    #6 0x475699 in dwz_files dwz.c:16417
    #7 0x4759fc in main dwz.c:16458
    #8 0x7f7ab8c41349 in __libc_start_main (/lib64/libc.so.6+0x24349)

SUMMARY: AddressSanitizer: 3360 byte(s) leaked in 12 allocation(s).
...

A more concrete way to show some of the leaks is by using this patch on
build_abbrevs:
...
+  assert (cu->cu_new_abbrev == NULL);
   cu->cu_new_abbrev = h;
   return 0;
 }
...
which triggers here:
...
 #4  0x00000000004211b1 in build_abbrevs (cu=0x7ffff65f0e38, t=0x64e640,
     ndies=0x7fffffffd81c, vec=0x649280 <ob2>) at dwz.c:11239
 #5  0x0000000000421db2 in compute_abbrevs (dso=0x0) at dwz.c:11511
 #6  0x000000000042fa2c in write_multifile (dso=0x64c210)
     at dwz.c:15104
...

We could just do a htab_delete in build_abbrevs, which takes care of all the
leaks detected by the assert.

But write_multifile drops CUs from the cu list if
cu->cu_die->die_no_multifile == 1, and if a dropped CU has cu->cu_new_abbrev
!= NULL then cu_new_abbrev is still leaked.

Fix this by calling htab_delete in the loop that drops the CUs.

Committed to trunk.

Thanks,
- Tom

Fix memory leak in write_multifile

2021-03-24  Tom de Vries  <tdevries@suse.de>

	PR dwz/27643
	* dwz.c (write_multifile): Clean up cu->cu_new_abbrev to fix memory
	leak.

---
 dwz.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/dwz.c b/dwz.c
index c115b54..b212d6d 100644
--- a/dwz.c
+++ b/dwz.c
@@ -15092,10 +15092,15 @@ write_multifile (DSO *dso)
       dw_cu_ref *cup;
 
       for (cup = &first_cu; *cup && (*cup)->cu_kind != CU_TYPES; )
-	if ((*cup)->cu_die->die_no_multifile == 0)
-	  cup = &(*cup)->cu_next;
-	else
-	  *cup = (*cup)->cu_next;
+	{
+	  if ((*cup)->cu_new_abbrev)
+	    htab_delete ((*cup)->cu_new_abbrev);
+
+	  if ((*cup)->cu_die->die_no_multifile == 0)
+	    cup = &(*cup)->cu_next;
+	  else
+	    *cup = (*cup)->cu_next;
+	}
       *cup = NULL;
       multifile_mode = MULTIFILE_MODE_WR;
       if (tracing)