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(This is a backport of https://gcc.gnu.org/pipermail/gcc-patches/2022-September/601059.html) After the prior libgfortran memory allocator preparation patch, this is the actual patch that organizes unified_shared_memory allocation into libgfortran. In the current OpenMP requires implementation, the requires_mask is collected through offload LTO processing, and presented to libgomp when registering offload images through GOMP_offload_register_ver() (called by the mkoffload generated constructor linked into the program binary) This means that the only reliable place to access omp_requires_mask is in GOMP_offload_register_ver, however since it is called through an ELF constructor in the *main program*, this runs later than libgfortran/runtime/main.c:init() constructor, and because some libgfortran init actions there start allocating memory, this can cause more deallocation errors later. Another issue is that CUDA appears to be registering some cleanup actions using atexit(), which forces libgomp to register gomp_target_fini() using atexit as well (to properly run before the underlying CUDA stuff disappears). This happens to us here as well. In summary we need to: (1) order libgfortran init actions after omp_requires_mask processing is done, and (2) order libgfortran cleanup actions before gomp_target_fini, to properly deallocate stuff without crashing. We implement this by creating callback registering functions exported from libgomp to libgfortran, basically to register libgfortran init/fini actions into libgomp to run. Inside GOMP_offload_register_ver, after omp_requires_mask processing is done, we call into libgfortran through a new _gfortran_mem_allocators_init function to insert the omp_free/alloc/etc. based allocators into the Fortran runtime, when GOMP_REQUIRES_UNIFIED_SHARED_MEMORY is set. All symbol references between libgfortran/libgomp are defined with weak symbols. Test of the weak symbols are also used to determine if the other library exists in this program. For the final case where we have an OpenMP program that does NOT have offloading, we cannot passively determine in libgomp/libgfortran whether offloading exists or not, only the main program itself can, by seeing if the hidden __OFFLOAD_TABLE__ exists. But those with no offloading will not have those callback properly run (because of no offload image loading) Therefore the solution here is a constructor added into the crtoffloadend.o fragment that does a "null" call of GOMP_offload_register_ver, solely for triggering the post-offload_register callbacks when __OFFLOAD_TABLE__ is NULL. (crtoffloadend.o Makefile rule is adjusted to compile with PIC due to this) libgcc/ChangeLog: * Makefile.in (crtoffloadend$(objext)): Add $(PICFLAG) to compile rule. * offloadstuff.c (GOMP_offload_register_ver): Add declaration of weak symbol. (__OFFLOAD_TABLE__): Likewise. (init_non_offload): New function. libgfortran/ChangeLog: * gfortran.map (GFORTRAN_13): New namespace. (_gfortran_mem_allocators_init): New name inside GFORTRAN_14. * libgfortran.h (mem_allocators_init): New exported declaration. * runtime/main.c (do_init): Rename from init, add run-once guard code. (cleanup): Add run-once guard code. (GOMP_post_offload_register_callback): Declare weak symbol. (GOMP_pre_gomp_target_fini_callback): Likewise. (init): New constructor to register offload callbacks, or call do_init when not OpenMP. * runtime/memory.c (gfortran_malloc): New pointer variable. (gfortran_calloc): Likewise. (gfortran_realloc): Likewise. (gfortran_free): Likewise. (mem_allocators_init): New function. (xmalloc): Use gfortran_malloc. (xmallocarray): Use gfortran_malloc. (xcalloc): Use gfortran_calloc. (xrealloc): Use gfortran_realloc. (xfree): Use gfortran_free. libgomp/ChangeLog: * libgomp.map (GOMP_5.1.2): New version namespace. (GOMP_post_offload_register_callback): New name inside GOMP_5.1.2. (GOMP_pre_gomp_target_fini_callback): Likewise. (GOMP_DEFINE_CALLBACK_SET): Macro to define callback set. (post_offload_register): Define callback set for after offload image register. (pre_gomp_target_fini): Define callback set for before gomp_target_fini is called. (libgfortran_malloc_usm): New function. (libgfortran_calloc_usm): Likewise (libgfortran_realloc_usm): Likewise (libgfortran_free_usm): Likewise. (_gfortran_mem_allocators_init): Declare weak symbol. (gomp_libgfortran_omp_allocators_init): New function. (GOMP_offload_register_ver): Add handling of host_table == NULL, calling into libgfortran to set unified_shared_memory allocators, and execution of post_offload_register callbacks. (gomp_target_init): Register all pre_gomp_target_fini callbacks to run at end of main using atexit(). * testsuite/libgomp.fortran/target-unified_shared_memory-1.f90: New test.
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