Hi,
with Jan's patch commited in r278878 we can use symver attribute for functions
and variables. The symver attribute is designed for replacing toplevel asm
statements containing ".symver" which may be removed by LTO. Unfortunately,
a quick test shown GCC still generates buggy so file with LTO and new symver
attribute.
Two issues:
1. The symver node in symtab is marked as PREVAILING_DEF_IRONLY (no EXP) and
then removed by LTO.
2. The actual function body implementing the symver-ed function is also marked
as PREVAILING_DEF_IRONLY and then removed or marked as local. So no ".globl"
directive is outputed for it.
Both issue cause symbols with symver missing in DSO (with LTO enabled).
I modified fuse-3.9.0 code to use new symver attribute and tried to build it
with GCC trunk and LTO. The result is a buggy DSO. With this patch applied,
fuse-3.9.0 can be built with LTO enabled and no problem.
I'll test symver patch and this patch with more packages.
Bootstrapped/regtested x86_64-linux. I'm not a maintainer.
gcc/ChangeLog:
2019-12-17 Xi Ruoyao <xry...@mengyan1223.wang>
* cgraph.h (symtab_node::used_from_object_file_p): Symver nodes are
part of DSO ABI so always used by non-LTO object files.
* ipa-visibility.c (cgraph_externally_visible_p): Functions with symver
attributes should always be visible.
Index: gcc/cgraph.h
===================================================================
--- gcc/cgraph.h (revision 279452)
+++ gcc/cgraph.h (working copy)
@@ -2682,7 +2682,7 @@ symtab_node::used_from_object_file_p (vo
{
if (!TREE_PUBLIC (decl) || DECL_EXTERNAL (decl))
return false;
- if (resolution_used_from_other_file_p (resolution))
+ if (symver || resolution_used_from_other_file_p (resolution))
return true;
return false;
}
Index: gcc/ipa-visibility.c
===================================================================
--- gcc/ipa-visibility.c (revision 279452)
+++ gcc/ipa-visibility.c (working copy)
@@ -216,6 +216,8 @@ cgraph_externally_visible_p (struct cgra
return true;
if (lookup_attribute ("noipa", DECL_ATTRIBUTES (node->decl)))
return true;
+ if (lookup_attribute ("symver", DECL_ATTRIBUTES (node->decl)))
+ return true;
if (TARGET_DLLIMPORT_DECL_ATTRIBUTES
&& lookup_attribute ("dllexport",
DECL_ATTRIBUTES (node->decl)))
--
Xi Ruoyao <xry...@mengyan1223.wang>
School of Aerospace Science and Technology, Xidian University
