https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97179
Bug ID: 97179
Summary: [LTO][Offloading] LTO's ltrans partiitioning causes
link errors for offload_vars + offload_funcs
("undefined reference")
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Keywords: openmp
Severity: normal
Priority: P3
Component: lto
Assignee: unassigned at gcc dot gnu.org
Reporter: burnus at gcc dot gnu.org
CC: jakub at gcc dot gnu.org, marxin at gcc dot gnu.org
Target Milestone: ---
Offloading creates two tables – which always have to be output (force_output =
1) and have to match between host and offloading device. The table contains
function/variable pointers.
When compiling a larger offloading project with -flto, the host code gets
partitioned at the WPA stage. This can cause that the offload tables
.gnu.offload_vars
.gnu.offload_funcs
end up in, e.g., a.ltrans0.o — While the function/variable ends up in, e.g.,
a.ltrans1.o
This gives errors such as:
./a.ltrans0.ltrans.o:(.gnu.offload_vars+0x4a0): undefined reference to
`yycon2'
and nm shows for a.ltrans0.ltrans.o
U yycon2
and for a.ltrans1.ltrans.o
0000000000003e58 b yycon2
Likewise for functions ("U" and "t" instead of "T").
Solution:
* Either make it visible for cross-file linkage
* or place all in the same ltrans partition.
For functions – but not for variables – the following patch helps:
--- a/gcc/lto-cgraph.c
+++ b/gcc/lto-cgraph.c
@@ -1793,6 +1794,9 @@ input_offload_tables (bool do_force_output)
LTO mode. */
if (do_force_output)
cgraph_node::get (fn_decl)->mark_force_output ();
+ /* ltrans might partition those such that they are in different
+ partions; to avoid link errors mark them as public. */
+ TREE_PUBLIC (fn_decl) = 1;
}
else if (tag == LTO_symtab_variable)
{
