[gcc r12-5890] amdgcn: Change offload variable table discovery

[gcc r12-5890] amdgcn: Change offload variable table discovery

[Andrew Stubbs]

https://gcc.gnu.org/g:4a87a8e4b13e979e7c8a626a8f4082715a48e21e

commit r12-5890-g4a87a8e4b13e979e7c8a626a8f4082715a48e21e
Author: Andrew Stubbs <ams@codesourcery.com>
Date:   Tue Nov 16 10:32:35 2021 +0000

    amdgcn: Change offload variable table discovery
    
    Up to now the libgomp GCN plugin has been finding the offload variables
    by using a symbol lookup, but the AMD runtime requires that the symbols are
    global for that to work. This was ensured by mkoffload as a post-procssing
    step, but the LLVM 13 assembler no longer accepts this in the case where the
    variable was previously declared differently.
    
    This patch switches to locating the symbols directly from the
    offload_var_table, which means that only one symbol needs to be forced
    global.
    
    This changes breaks the libgomp image compatibility so GOMP_VERSION_GCN has
    also been bumped.
    
    gcc/ChangeLog:
    
            * config/gcn/mkoffload.c (process_asm): Process the variable table
            completely differently.
            (process_obj): Encode the varaible data differently.
    
    include/ChangeLog:
    
            * gomp-constants.h (GOMP_VERSION_GCN): Bump.
    
    libgomp/ChangeLog:
    
            * plugin/plugin-gcn.c (struct gcn_image_desc): Remove global_variables.
            (GOMP_OFFLOAD_load_image): Locate the offload variables via the
            table, not individual symbols.

Diff:
---
 gcc/config/gcn/mkoffload.c  | 51 +++++++++++++++++----------------------------
 include/gomp-constants.h    |  2 +-
 libgomp/plugin/plugin-gcn.c | 39 ++++++++++++++++++----------------
 3 files changed, 41 insertions(+), 51 deletions(-)

diff --git a/gcc/config/gcn/mkoffload.c b/gcc/config/gcn/mkoffload.c
index b2e71ea5aa0..d609b7a6f9c 100644
--- a/gcc/config/gcn/mkoffload.c
+++ b/gcc/config/gcn/mkoffload.c
@@ -495,10 +495,8 @@ static void
 process_asm (FILE *in, FILE *out, FILE *cfile)
 {
   int fn_count = 0, var_count = 0, dims_count = 0, regcount_count = 0;
-  struct obstack fns_os, vars_os, varsizes_os, dims_os, regcounts_os;
+  struct obstack fns_os, dims_os, regcounts_os;
   obstack_init (&fns_os);
-  obstack_init (&vars_os);
-  obstack_init (&varsizes_os);
   obstack_init (&dims_os);
   obstack_init (&regcounts_os);
 
@@ -567,16 +565,11 @@ process_asm (FILE *in, FILE *out, FILE *cfile)
 	    unsigned varsize;
 	    if (sscanf (buf, " .8byte %ms\n", &varname))
 	      {
-		obstack_ptr_grow (&vars_os, varname);
+		fputs (buf, out);
 		fgets (buf, sizeof (buf), in);
 		if (!sscanf (buf, " .8byte %u\n", &varsize))
 		  abort ();
-		obstack_int_grow (&varsizes_os, varsize);
 		var_count++;
-
-		/* The HSA Runtime cannot locate the symbol if it is not
-		   exported from the kernel.  */
-		fprintf (out, "\t.global %s\n", varname);
 	      }
 	    break;
 	  }
@@ -595,7 +588,19 @@ process_asm (FILE *in, FILE *out, FILE *cfile)
 
       char dummy;
       if (sscanf (buf, " .section .gnu.offload_vars%c", &dummy) > 0)
-	state = IN_VARS;
+	{
+	  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;
       else if (sscanf (buf, " .amdgpu_metadata%c", &dummy) > 0)
@@ -622,7 +627,7 @@ process_asm (FILE *in, FILE *out, FILE *cfile)
 	  regcount.sgpr_count = regcount.vgpr_count = -1;
 	}
 
-      if (state == IN_CODE || state == IN_METADATA)
+      if (state == IN_CODE || state == IN_METADATA || state == IN_VARS)
 	fputs (buf, out);
     }
 
@@ -633,24 +638,7 @@ process_asm (FILE *in, FILE *out, FILE *cfile)
   fprintf (cfile, "#include <stdlib.h>\n");
   fprintf (cfile, "#include <stdbool.h>\n\n");
 
-  char **vars = XOBFINISH (&vars_os, char **);
-  unsigned *varsizes = XOBFINISH (&varsizes_os, unsigned *);
-  fprintf (cfile,
-	   "static const struct global_var_info {\n"
-	   "  const char *name;\n"
-	   "  void *address;\n"
-	   "} vars[] = {\n");
-  int i;
-  for (i = 0; i < var_count; ++i)
-    {
-      const char *sep = i < var_count - 1 ? "," : " ";
-      fprintf (cfile, "  { \"%s\", NULL }%s /* size: %u */\n", vars[i], sep,
-	       varsizes[i]);
-    }
-  fprintf (cfile, "};\n\n");
-
-  obstack_free (&vars_os, NULL);
-  obstack_free (&varsizes_os, NULL);
+  fprintf (cfile, "static const int gcn_num_vars = %d;\n\n", var_count);
 
   /* Dump out function idents.  */
   fprintf (cfile, "static const struct hsa_kernel_description {\n"
@@ -661,6 +649,7 @@ process_asm (FILE *in, FILE *out, FILE *cfile)
 	   "} gcn_kernels[] = {\n  ");
   dim.d[0] = dim.d[1] = dim.d[2] = 0;
   const char *comma;
+  int i;
   for (comma = "", i = 0; i < fn_count; comma = ",\n  ", i++)
     {
       /* Find if we recorded dimensions for this function.  */
@@ -732,13 +721,11 @@ process_obj (FILE *in, FILE *cfile)
 	   "  unsigned kernel_count;\n"
 	   "  const struct hsa_kernel_description *kernel_infos;\n"
 	   "  unsigned global_variable_count;\n"
-	   "  const struct global_var_info *global_variables;\n"
 	   "} target_data = {\n"
 	   "  &gcn_image,\n"
 	   "  sizeof (gcn_kernels) / sizeof (gcn_kernels[0]),\n"
 	   "  gcn_kernels,\n"
-	   "  sizeof (vars) / sizeof (vars[0]),\n"
-	   "  vars\n"
+	   "  gcn_num_vars\n"
 	   "};\n\n");
 
   fprintf (cfile,
diff --git a/include/gomp-constants.h b/include/gomp-constants.h
index 9e7db69f082..2cf0919a7fb 100644
--- a/include/gomp-constants.h
+++ b/include/gomp-constants.h
@@ -274,7 +274,7 @@ enum gomp_map_kind
 #define GOMP_VERSION	1
 #define GOMP_VERSION_NVIDIA_PTX 1
 #define GOMP_VERSION_INTEL_MIC 0
-#define GOMP_VERSION_GCN 1
+#define GOMP_VERSION_GCN 2
 
 #define GOMP_VERSION_PACK(LIB, DEV) (((LIB) << 16) | (DEV))
 #define GOMP_VERSION_LIB(PACK) (((PACK) >> 16) & 0xffff)
diff --git a/libgomp/plugin/plugin-gcn.c b/libgomp/plugin/plugin-gcn.c
index 9e7377c91f9..694862b97f4 100644
--- a/libgomp/plugin/plugin-gcn.c
+++ b/libgomp/plugin/plugin-gcn.c
@@ -392,7 +392,6 @@ struct gcn_image_desc
   const unsigned kernel_count;
   struct hsa_kernel_description *kernel_infos;
   const unsigned global_variable_count;
-  struct global_var_info *global_variables;
 };
 
 /* This enum mirrors the corresponding LLVM enum's values for all ISAs that we
@@ -3365,37 +3364,41 @@ GOMP_OFFLOAD_load_image (int ord, unsigned version, const void *target_data,
   if (!create_and_finalize_hsa_program (agent))
     return -1;
 
-  for (unsigned i = 0; i < var_count; i++)
+  if (var_count > 0)
     {
-      struct global_var_info *v = &image_desc->global_variables[i];
-      GCN_DEBUG ("Looking for variable %s\n", v->name);
-
       hsa_status_t status;
       hsa_executable_symbol_t var_symbol;
       status = hsa_fns.hsa_executable_get_symbol_fn (agent->executable, NULL,
-						     v->name, agent->id,
+						     ".offload_var_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 var_addr;
-      uint32_t var_size;
+      uint64_t var_table_addr;
       status = hsa_fns.hsa_executable_symbol_get_info_fn
-	(var_symbol, HSA_EXECUTABLE_SYMBOL_INFO_VARIABLE_ADDRESS, &var_addr);
+	(var_symbol, HSA_EXECUTABLE_SYMBOL_INFO_VARIABLE_ADDRESS,
+	 &var_table_addr);
       if (status != HSA_STATUS_SUCCESS)
 	hsa_fatal ("Could not extract a variable from its symbol", status);
-      status = hsa_fns.hsa_executable_symbol_get_info_fn
-	(var_symbol, HSA_EXECUTABLE_SYMBOL_INFO_VARIABLE_SIZE, &var_size);
-      if (status != HSA_STATUS_SUCCESS)
-	hsa_fatal ("Could not extract a variable size from its symbol", status);
 
-      pair->start = var_addr;
-      pair->end = var_addr + var_size;
-      GCN_DEBUG ("Found variable %s at %p with size %u\n", v->name,
-		 (void *)var_addr, var_size);
-      pair++;
+      struct {
+	uint64_t addr;
+	uint64_t size;
+      } var_table[var_count];
+      GOMP_OFFLOAD_dev2host (agent->device_id, var_table,
+			     (void*)var_table_addr, sizeof (var_table));
+
+      for (unsigned i = 0; i < var_count; i++)
+	{
+	  pair->start = var_table[i].addr;
+	  pair->end = var_table[i].addr + var_table[i].size;
+	  GCN_DEBUG ("Found variable at %p with size %lu\n",
+		     (void *)var_table[i].addr, var_table[i].size);
+	  pair++;
+	}
     }
 
   GCN_DEBUG ("Looking for variable %s\n", STRINGX (GOMP_DEVICE_NUM_VAR));