It was pointed out by Markus that the EH emergency pool is not
kept sorted and fully merged properly for the cases of freeing
an entry before the first free entry and for the cases where
merging with the immediate successor and for the case with
merging with both successor and predecessor is possible.
The following patch attempts to fix this.
Bootstrap and regtest running on x86_64-unknown-linux-gnu.
Ok for trunk? (given low / close to no testing coverage
extra close eyes wanted!)
Reporter says maybe it can't happen in real-life as it requires
EH deallocation order not be the reverse of allocation order.
I don't know enough here for a quick guess but "in C++ everything
is possible" ;)
Thanks,
Richard.
2017-05-12 Richard Biener <rguent...@suse.de>
Markus Eisenmann <meisenmann....@fh-salzburg.ac.at>
PR libstdc++/80721
* libsupc++/eh_alloc.cc (pool::free): Keep list properly
sorted and add missing freelist item merging cases.
Index: libstdc++-v3/libsupc++/eh_alloc.cc
===================================================================
--- libstdc++-v3/libsupc++/eh_alloc.cc (revision 247951)
+++ libstdc++-v3/libsupc++/eh_alloc.cc (working copy)
@@ -194,13 +194,17 @@ namespace
allocated_entry *e = reinterpret_cast <allocated_entry *>
(reinterpret_cast <char *> (data) - offsetof (allocated_entry, data));
std::size_t sz = e->size;
- if (!first_free_entry)
+ if (!first_free_entry
+ || (reinterpret_cast <char *> (e) + sz
+ < reinterpret_cast <char *> (first_free_entry)))
{
- // If the free list is empty just put the entry there.
+ // If the free list is empty or the entry is before the
+ // first element and cannot be merged with it add it as
+ // the first free entry.
free_entry *f = reinterpret_cast <free_entry *> (e);
new (f) free_entry;
f->size = sz;
- f->next = NULL;
+ f->next = first_free_entry;
first_free_entry = f;
}
else if (reinterpret_cast <char *> (e) + sz
@@ -224,9 +228,17 @@ namespace
> reinterpret_cast <char *> (e) + sz);
fe = &(*fe)->next)
;
+ // If we can merge the next block into us do so and continue
+ // with the cases below.
+ if (reinterpret_cast <char *> (e) + sz
+ == reinterpret_cast <char *> ((*fe)->next))
+ {
+ sz += (*fe)->next->size;
+ (*fe)->next = (*fe)->next->next;
+ }
if (reinterpret_cast <char *> (*fe) + (*fe)->size
== reinterpret_cast <char *> (e))
- /* Merge with the freelist entry. */
+ // Merge with the freelist entry.
(*fe)->size += sz;
else
{
