Seems to be a CUDA JIT issue - which is fixed by adding a dummy procedure.
Lightly tested with 4 systems at hand, where 2 failed before. One had 10.2 and the other had some ancient CUDA where 'nvptx-smi' did not print a CUDA version and requires -mptx=3.1. (I did check that offloading indeed happened and no hostfallback was done.) OK for mainline? Tobias ----------------- Siemens Electronic Design Automation GmbH; Anschrift: Arnulfstraße 201, 80634 München; Gesellschaft mit beschränkter Haftung; Geschäftsführer: Thomas Heurung, Frank Thürauf; Sitz der Gesellschaft: München; Registergericht München, HRB 106955
nvptx/mkoffload.cc: Add dummy proc for OpenMP rev-offload table [PR108098] Seemingly, the ptx JIT of CUDA <= 10.2 replaces function pointers in global variables by NULL if a translation does not contain any executable code. It works with CUDA 11.1. The code of this commit is about reverse offload; having NULL values disables the side of reverse offload during image load. Solution is the same as found by Thomas for a related issue: Adding a dummy procedure. Cf. the PR of this issue and Thomas' patch "nvptx: Support global constructors/destructors via 'collect2'" https://gcc.gnu.org/pipermail/gcc-patches/2022-December/607749.html As that approach also works here: Co-authored-by: Thomas Schwinge <tho...@codesourcery.com> gcc/ PR libgomp/108098 * config/nvptx/mkoffload.cc (process): Emit dummy procedure alongside reverse-offload function table to prevent NULL values of the function addresses. --- gcc/config/nvptx/mkoffload.cc | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/gcc/config/nvptx/mkoffload.cc b/gcc/config/nvptx/mkoffload.cc index 5d89ba8..8306aa0 100644 --- a/gcc/config/nvptx/mkoffload.cc +++ b/gcc/config/nvptx/mkoffload.cc @@ -357,6 +357,20 @@ process (FILE *in, FILE *out, uint32_t omp_requires) fputc (sm_ver2[i], out); fprintf (out, "\"\n\t\".file 1 \\\"<dummy>\\\"\"\n"); + /* WORKAROUND - see PR 108098 + It seems as if older CUDA JIT compiler optimizes the function pointers + in offload_func_table to NULL, which can be prevented by adding a + dummy procedure. With CUDA 11.1, it seems to work fine without + workaround while CUDA 10.2 as some ancient version have need the + workaround. Assuming CUDA 11.0 fixes it, emitting it could be + restricted to 'if (sm_ver2[0] < 8 && version2[0] < 7)' as sm_80 and + PTX ISA 7.0 are new in CUDA 11.0; for 11.1 it would be sm_86 and + PTX ISA 7.1. */ + fprintf (out, "\n\t\".func __dummy$func ( );\"\n"); + fprintf (out, "\t\".func __dummy$func ( )\"\n"); + fprintf (out, "\t\"{\"\n"); + fprintf (out, "\t\"}\"\n"); + size_t fidx = 0; for (id = func_ids; id; id = id->next) {
