https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94251
Bug ID: 94251
Summary: [OpenMP] 'target link' fails at run time /
libgomp.c/target-link-1.c fails on GCN
Product: gcc
Version: 10.0
Status: UNCONFIRMED
Keywords: openmp, wrong-code
Severity: normal
Priority: P3
Component: libgomp
Assignee: unassigned at gcc dot gnu.org
Reporter: burnus at gcc dot gnu.org
CC: jakub at gcc dot gnu.org
Target Milestone: ---
Follow-up to PR 94233.
The test case libgomp.c/target-link-1.c fails with AMDGCN with:
"libgomp: Cannot map target variables (size mismatch)"
------------------------
That's in libgomp/target.c's gomp_load_image_to_device:
/* Most significant bit of the size in host and target tables marks
"omp declare target link" variables. */
const uintptr_t link_bit = 1ULL << (sizeof (uintptr_t) * __CHAR_BIT__ - 1);
const uintptr_t size_mask = ~link_bit;
struct addr_pair *target_var = &target_table[num_funcs + i];
uintptr_t target_size = target_var->end - target_var->start;
if ((uintptr_t) host_var_table[i * 2 + 1] != target_size)
gomp_fatal ("Cannot map target variables (size mismatch)");
-----------------------
The code clearly assumes that the link_bit is also present in target_size –
which is not only visible in the quoted condition but also for:
k->refcount = target_size & link_bit ? REFCOUNT_LINK : REFCOUNT_INFINITY;
While for the host data, that's not assumed as one masks the data:
k->host_end
= k->host_start + (size_mask & (uintptr_t) host_var_table[i * 2 + 1]);
I think it should be:
* no link mask in target_var->end / target_size
* Use 'host_var_table[i*2+1] & link_bit' in the refcount expression
* Use '& link_bit' for the size comparison.
------------------------
The passed arguments are fine:
(gdb) p host_var_table[1]
$15 = (void *) 0x8000000000000008
(gdb) p host_var_table[3]
$16 = (void *) 0x80000000000000d8
(gdb) p host_var_table[5]
$17 = (void *) 0x4
(gdb) p host_var_table[7]
$18 = (void *) 0x8000000000000004
Namely: 'd' = 2*int = 8, 'c' = 27*double = 216 = 0xD8, 'a' and 'b' being
int=4.,
'b' is 'to', the rest is 'link'.
However, at least with AMDGCN, target_size == 8 for all variables. At a glance,
the code in GOMP_OFFLOAD_load_image looks fine, but:
image_desc->global_variables[i]->name is "d_linkptr" and not "d".
That variable is generated by lto/lto.c's offload_handle_link_vars as
tree type = build_pointer_type (TREE_TYPE (var->decl));
where var->decl is "d" in this case.
Thus, it is not surprising that the size is always 8.
* * *
Looking at the other plugins, they seems to work mostly likewise [get bit size
correctly]:
* hsa: global variables not processed in load_image, i.e.
target_table not updated for the global variables!
* nvptx: cuModuleGetGlobal called, look fine.
