[Patch][2/3] GCN: libgomp+mkoffload.cc: Prepare for reverse offload fn lookup

[Tobias Burnus <tobias@codesourcery.com>]

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On 25.08.22 16:54, Tobias Burnus wrote:

The attached patch prepare for reverse-offload device->host
function-address lookup by requesting (if needed) the on-device address.


This patch adds the actual implementation for GCN. A variant would be
to only generate .offload_func_table inside mkoffload when
OMP_REQUIRES_REVERSE_OFFLOAD has been requested.

This is currently effectively a no op as with [1/3] patch, always NULL
is passed and as GOMP_OFFLOAD_get_num_devices returns <= 0 as soon as
'omp requires reverse_offload' has been specified.

OK for mainline?

Tobias


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GCN: libgomp+mkoffload.cc: Prepare for reverse offload fn lookup

Add support to GCN for reverse lookup of function name to prepare for
'omp target device(ancestor:1)'.

gcc/ChangeLog:

	* config/gcn/mkoffload.cc (process_asm): Create .offload_func_table,
	similar to pre-existing .offload_var_table.

libgomp/ChangeLog:

	* plugin/plugin-gcn.c (GOMP_OFFLOAD_load_image): Read
	.offload_func_table to populate rev_fn_table when requested.

 gcc/config/gcn/mkoffload.cc | 11 ++++++++++-
 libgomp/plugin/plugin-gcn.c | 26 +++++++++++++++++++++++++-
 2 files changed, 35 insertions(+), 2 deletions(-)
diff --git a/gcc/config/gcn/mkoffload.cc b/gcc/config/gcn/mkoffload.cc
index 4206448703a..24d327355e3 100644
--- a/gcc/config/gcn/mkoffload.cc
+++ b/gcc/config/gcn/mkoffload.cc
@@ -537,63 +537,72 @@ process_asm (FILE *in, FILE *out, FILE *cfile)
 	case IN_VARS:
 	  {
 	    char *varname;
 	    unsigned varsize;
 	    if (sscanf (buf, " .8byte %ms\n", &varname))
 	      {
 		fputs (buf, out);
 		fgets (buf, sizeof (buf), in);
 		if (!sscanf (buf, " .8byte %u\n", &varsize))
 		  abort ();
 		var_count++;
 	      }
 	    break;
 	  }
 	case IN_FUNCS:
 	  {
 	    char *funcname;
 	    if (sscanf (buf, "\t.8byte\t%ms\n", &funcname))
 	      {
+		fputs (buf, out);
 		obstack_ptr_grow (&fns_os, funcname);
 		fn_count++;
 		continue;
 	      }
 	    break;
 	  }
 	}
 
       char dummy;
       if (sscanf (buf, " .section .gnu.offload_vars%c", &dummy) > 0)
 	{
 	  state = IN_VARS;
 
 	  /* Add a global symbol to allow plugin-gcn.c to locate the table
 	     at runtime.  It can't use the "offload_var_table.N" emitted by
 	     the compiler because a) they're not global, and b) there's one
 	     for each input file combined into the binary.  */
 	  fputs (buf, out);
 	  fputs ("\t.global .offload_var_table\n"
 		 "\t.type .offload_var_table, @object\n"
 		 ".offload_var_table:\n",
 		 out);
 	}
       else if (sscanf (buf, " .section .gnu.offload_funcs%c", &dummy) > 0)
-	state = IN_FUNCS;
+	{
+	  state = IN_FUNCS;
+	  /* Likewise for .gnu.offload_vars; used for reverse offload. */
+	  fputs (buf, out);
+	  fputs ("\t.global .offload_func_table\n"
+		 "\t.type .offload_func_table, @object\n"
+		 ".offload_func_table:\n",
+		 out);
+	}
       else if (sscanf (buf, " .amdgpu_metadata%c", &dummy) > 0)
 	{
 	  state = IN_METADATA;
 	  regcount.kernel_name = NULL;
 	  regcount.sgpr_count = regcount.vgpr_count = -1;
 	}
       else if (sscanf (buf, " .section %c", &dummy) > 0
 	       || sscanf (buf, " .text%c", &dummy) > 0
 	       || sscanf (buf, " .bss%c", &dummy) > 0
 	       || sscanf (buf, " .data%c", &dummy) > 0
 	       || sscanf (buf, " .ident %c", &dummy) > 0)
 	state = IN_CODE;
       else if (sscanf (buf, " .end_amdgpu_metadata%c", &dummy) > 0)
 	{
 	  state = IN_CODE;
 	  gcc_assert (regcount.kernel_name != NULL
 		      && regcount.sgpr_count >= 0
 		      && regcount.vgpr_count >= 0);
 	  obstack_grow (&regcounts_os, &regcount, sizeof (regcount));
diff --git a/libgomp/plugin/plugin-gcn.c b/libgomp/plugin/plugin-gcn.c
index 363e2950649..00603981866 100644
--- a/libgomp/plugin/plugin-gcn.c
+++ b/libgomp/plugin/plugin-gcn.c
@@ -3353,7 +3353,7 @@ GOMP_OFFLOAD_init_device (int n)
 int
 GOMP_OFFLOAD_load_image (int ord, unsigned version, const void *target_data,
 			 struct addr_pair **target_table,
-			 uint64_t **rev_fn_table __attribute__((unused)))
+			 uint64_t **rev_fn_table)
 {
   if (GOMP_VERSION_DEV (version) != GOMP_VERSION_GCN)
     {
@@ -3520,6 +3520,30 @@ GOMP_OFFLOAD_load_image (int ord, unsigned version, const void *target_data,
   if (module->fini_array_func)
     kernel_count--;
 
+  if (rev_fn_table != NULL && kernel_count == 0)
+    *rev_fn_table = NULL;
+  else if (rev_fn_table != NULL)
+    {
+      hsa_status_t status;
+      hsa_executable_symbol_t var_symbol;
+      status = hsa_fns.hsa_executable_get_symbol_fn (agent->executable, NULL,
+						     ".offload_func_table",
+						     agent->id, 0, &var_symbol);
+      if (status != HSA_STATUS_SUCCESS)
+	hsa_fatal ("Could not find symbol for variable in the code object",
+		   status);
+      uint64_t fn_table_addr;
+      status = hsa_fns.hsa_executable_symbol_get_info_fn
+	(var_symbol, HSA_EXECUTABLE_SYMBOL_INFO_VARIABLE_ADDRESS,
+	 &fn_table_addr);
+      if (status != HSA_STATUS_SUCCESS)
+	hsa_fatal ("Could not extract a variable from its symbol", status);
+      *rev_fn_table = GOMP_PLUGIN_malloc (kernel_count * sizeof (uint64_t));
+      GOMP_OFFLOAD_dev2host (agent->device_id, *rev_fn_table,
+			     (void*) fn_table_addr,
+			     kernel_count * sizeof (uint64_t));
+    }
+
   return kernel_count + var_count + other_count;
 }