honza,
this is the fix for the partitioned WPA bug I was tracking down.
We have base and complete dtors sharing a comdat group (one's an alias
for the other). The linker tells us the complete dtor is
PREVAILING_DEF, as it's referenced from some other library. The base
dtor is UNKNOWN.
We therefore internalize the base dtor, making it PREVAILING_DEF_IRONLY
and split the comdat group. But the comdat group splitting also
internalizes the complete dtor /and/ it does so inconsistently.
The bug manifested at runtime w/o link error as the complete dtor
resolved to zero in the final link from wpa partitions that didn't
contain its definition. (For extra fun, that was via a call to
__cxa_at_exit registering a null function pointer, and getting the
subsequent seg fault at program exit.) When we created WPA partitions
node->externally_visible was still set, so we thought the
now-internalized complete dtor was still externally visible -- but
varasm looks at the DECL itself and emits an internal one. Plus the
references to it were weak (& now hidden), so resolved to zero, rather
than link error. And the external library either had its own definition
which then prevailed for it. All rather 'ew'.
Anyway, this patch does 3 things
1) Moves the next->unique_name adjustment to before make_decl_local for
members of the comdat group -- that matches the behaviour of the decl of
interest itself.
2) For LDPR_PREVAILING_DEF members we don't make_decl_local, but instead
clear DECL_COMDAT and DECL_WEAK. Thus forcing this decl to be the
prevailing decl in the final link
3) For decls we localize, we also clear node->externally_visible and
node->force_by_abi. That matches the behavior for the decl of interest
too and will clue the wpa partitioning logic into knowing it needs to
hidden-externalize the decl.
ok?
nathan
--
Nathan Sidwell
2017-01-18 Nathan Sidwell <nat...@acm.org>
* ipa-visibility.c (localize_node): Set comdat's unique name
before adjusting resolution. Make PREVAILING_DEF members strongly
public. Set visibility to false for localized decls.
Index: ipa-visibility.c
===================================================================
--- ipa-visibility.c (revision 244546)
+++ ipa-visibility.c (working copy)
@@ -542,16 +542,32 @@ localize_node (bool whole_program, symta
for (symtab_node *next = node->same_comdat_group;
next != node; next = next->same_comdat_group)
{
- next->set_comdat_group (NULL);
- if (!next->alias)
- next->set_section (NULL);
- if (!next->transparent_alias)
- next->make_decl_local ();
next->unique_name
|= ((next->resolution == LDPR_PREVAILING_DEF_IRONLY
|| next->resolution == LDPR_PREVAILING_DEF_IRONLY_EXP)
&& TREE_PUBLIC (next->decl)
&& !flag_incremental_link);
+
+ next->set_comdat_group (NULL);
+ if (!next->alias)
+ next->set_section (NULL);
+ if (next->transparent_alias)
+ /* Do nothing. */;
+ else if (next->resolution == LDPR_PREVAILING_DEF)
+ {
+ /* Make this a strong defn, so the external
+ users don't mistakenly choose some other
+ instance. */
+ DECL_COMDAT (next->decl) = false;
+ DECL_WEAK (next->decl) = false;
+ }
+ else
+ {
+ next->externally_visible = false;
+ next->forced_by_abi = false;
+ next->resolution = LDPR_PREVAILING_DEF_IRONLY;
+ next->make_decl_local ();
+ }
}
/* Now everything's localized, the grouping has no meaning, and
