Junio C Hamano wrote:
> Thanks.
Thanks for taking the time to look into this!
>
> Since you can build and run git yourself, can I ask you to run another
> experiment with this one-liner patch applied?
It appears that a segfault still happens with your patch applied, but
this time it is caught:
tolsen@neurofunk:~/git/site-build-dav-sync-05 [git:build-dav-sync-05]$
git merge origin/deployed
error: merge-recursive died of signal 11
Merge with strategy recursive failed.
tolsen@neurofunk:~/git/site-build-dav-sync-05 [git:build-dav-sync-05]$
> "common = NULL" means merged_common_ancestors->tree is NULL in the caller.
> Somebody is passing a bogus commit in "ca" (aka common ancestors) list
> when calling merge_recursive(), or forgetting to parse them before calling
> it. In your debugger could you find out where it comes from and what it
> has before this call into merge_trees() is made? Specifically, what the
> "ca" list at 0x7b3c00 contains, and how "merged_common_ancestors" at
> 0x121e360 looks like. in this trace we see below:
Here is the replay of the flow of execution from the first time we enter
merge_recursive(). The repository has been modified slightly so the
pointers are different this time but the segfault is still happening
(I'll stop modifying the repository now ;-) .
Upon entering merge_recursive() for the first time, ca is a two-item
list and both items have non-null trees:
Breakpoint 1, merge_recursive (o=0x7fffffffd560, h1=0x793350,
h2=0x7932c0, ca=0x7b4a40, result=0x7fffffffd5d8) at merge-recursive.c:1286
(gdb) p *ca
$1 = {item = 0x793db8, next = 0x7b4a20}
(gdb) p *(ca->next)
$2 = {item = 0x793aa0, next = 0x0}
(gdb) p ca->item->tree
$3 = (struct tree *) 0x77be10
(gdb) p ca->next->item->tree
$4 = (struct tree *) 0x77b488
(gdb)
Then on line 1303, the head of ca is popped off into
merged_common_ancestors:
Breakpoint 2, merge_recursive (o=0x7fffffffd560, h1=0x793350,
h2=0x7932c0, ca=0x7b4a20, result=0x7fffffffd5d8) at merge-recursive.c:1304
(gdb) list
1299 for (iter = ca; iter; iter = iter->next)
1300 output_commit_title(o, iter->item);
1301 }
1302
1303 merged_common_ancestors = pop_commit(&ca);
1304 if (merged_common_ancestors == NULL) {
1305 /* if there is no common ancestor, make an empty tree */
1306 struct tree *tree = xcalloc(1, sizeof(struct tree));
1307
1308 tree->object.parsed = 1;
(gdb) p merged_common_ancestors
$5 = (struct commit *) 0x793db8
(gdb) p ca
$8 = (struct commit_list *) 0x7b4a20
merge_recursive() is then called recursively at line 1329 with a pointer
to merged_common_ancestors passed as the "result" argument:
Breakpoint 3, merge_recursive (o=0x7fffffffd560, h1=0x793350,
h2=0x7932c0, ca=0x7b4a20, result=0x7fffffffd5d8) at merge-recursive.c:1329
(gdb) list
1324 discard_cache();
1325 saved_b1 = o->branch1;
1326 saved_b2 = o->branch2;
1327 o->branch1 = "Temporary merge branch 1";
1328 o->branch2 = "Temporary merge branch 2";
1329 merge_recursive(o, merged_common_ancestors, iter->item,
1330 NULL, &merged_common_ancestors);
1331 o->branch1 = saved_b1;
1332 o->branch2 = saved_b2;
1333 o->call_depth--;
(gdb)
In the second call to merged_common_ancestors(), result's pointee is
replaced by a commit with a null tree at line 1347:
Breakpoint 4, merge_recursive (o=0x7fffffffd560, h1=0x793db8,
h2=0x793aa0, ca=0x0, result=0x7fffffffd500) at merge-recursive.c:1347
(gdb) n
(gdb) p (*result)->tree
$10 = (struct tree *) 0x0
(gdb) list
1343 clean = merge_trees(o, h1->tree, h2->tree,
merged_common_ancestors->tree,
1344 &mrtree);
1345
1346 if (o->call_depth) {
1347 *result = make_virtual_commit(mrtree, "merged tree");
1348 commit_list_insert(h1, &(*result)->parents);
1349 commit_list_insert(h2, &(*result)->parents->next);
1350 }
1351 flush_output(o);
1352 return clean;
(gdb)
make_virtual_commit() is just setting its tree to mrtree:
Breakpoint 5, make_virtual_commit (tree=0x0, comment=0x5016fc "merged
tree") at merge-recursive.c:44
(gdb) list
39 * A virtual commit has (const char *)commit->util set to the name.
40 */
41
42 static struct commit *make_virtual_commit(struct tree *tree, const
char *comment)
43 {
44 struct commit *commit = xcalloc(1, sizeof(struct commit));
45 commit->tree = tree;
46 commit->util = (void*)comment;
47 /* avoid warnings */
48 commit->object.parsed = 1;
(gdb)
49 return commit;
50 }
At the beginning of merge_recursive(), the local mrtree appears to be
set to some globally defined mrtree which is not null:
Breakpoint 1, merge_recursive (o=0x7fffffffd560, h1=0x793db8,
h2=0x793aa0, ca=0x0, result=0x7fffffffd500) at merge-recursive.c:1286
(gdb) p mrtree
$13 = (struct tree *) 0x7ffff732d0ac
(gdb) list
1281 struct commit_list *iter;
1282 struct commit *merged_common_ancestors;
1283 struct tree *mrtree = mrtree;
1284 int clean;
1285
1286 if (show(o, 4)) {
1287 output(o, 4, "Merging:");
1288 output_commit_title(o, h1);
1289 output_commit_title(o, h2);
1290 }
(gdb)
Which leads me to believe the problem is in the call to merge_trees() at
line 1343:
Breakpoint 6, merge_recursive (o=0x7fffffffd560, h1=0x793db8,
h2=0x793aa0, ca=0x0, result=0x7fffffffd500) at merge-recursive.c:1343
(gdb) list
1338
1339 discard_cache();
1340 if (!o->call_depth)
1341 read_cache();
1342
1343 clean = merge_trees(o, h1->tree, h2->tree,
merged_common_ancestors->tree,
1344 &mrtree);
1345
1346 if (o->call_depth) {
1347 *result = make_virtual_commit(mrtree, "merged tree");
(gdb)
In merge_trees(), mrtree is the argument **result. It is at line 1255
that write_tree_from_memory nulls out the pointee of result:
Breakpoint 7, merge_trees (o=0x7fffffffd560, head=0x77be10,
merge=0x77b488, common=0x77c0b8, result=0x7fffffffd478) at
merge-recursive.c:1255
(gdb) p *result
$16 = (struct tree *) 0x7ffff732d0ac
(gdb) n
(gdb) p *result
$17 = (struct tree *) 0x0
(gdb) list
1252 clean = 1;
1253
1254 if (o->call_depth)
1255 *result = write_tree_from_memory(o);
1256
1257 return clean;
1258 }
1259
1260 static struct commit_list *reverse_commit_list(struct commit_list
*list)
1261 {
(gdb)
Then in write_tree_from_memory() we find the offending return NULL at
line 210:
Breakpoint 8, write_tree_from_memory (o=0x7fffffffd560) at
merge-recursive.c:210
(gdb) list
205 struct cache_entry *ce = active_cache[i];
206 if (ce_stage(ce))
207 output(o, 0, "%d %.*s", ce_stage(ce),
208 (int)ce_namelen(ce), ce->name);
209 }
210 return NULL;
211 }
212
213 if (!active_cache_tree)
214 active_cache_tree = cache_tree();
(gdb)
Let me know if you need any more information.
Thanks,
Tim
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