Implement LDPT_REGISTER_CLAIM_FILE_HOOK_V2 linker plugin hook [PR109128]

This is one part of the fix for PR109128, along with a corresponding
binutils's linker change.  Without this patch, what happens in the
linker, when an unused object in a .a file has offload data, is that
elf_link_is_defined_archive_symbol calls bfd_link_plugin_object_p,
which ends up calling the plugin's claim_file_handler, which then
records the object as one with offload data. That is, the linker never
decides to use the object in the first place, but use of this _p
interface (called as part of trying to decide whether to use the
object) results in the plugin deciding to use its offload data (and a
consequent mismatch in the offload data present at runtime).

The new hook allows the linker plugin to distinguish calls to
claim_file_handler that know the object is being used by the linker
(from ldmain.c:add_archive_element), from calls that don't know it's
being used by the linker (from elf_link_is_defined_archive_symbol); in
the latter case, the plugin should avoid recording the object as one
with offload data.

	PR middle-end/109128

	include/
	* plugin-api.h (ld_plugin_claim_file_handler_v2)
	(ld_plugin_register_claim_file_v2)
	(LDPT_REGISTER_CLAIM_FILE_HOOK_V2): New.
	(struct ld_plugin_tv): Add tv_register_claim_file_v2.

	lto-plugin/
	* lto-plugin.c (register_claim_file_v2): New.
	(claim_file_handler_v2): New.
	(claim_file_handler): Wrap claim_file_handler_v2.
	(onload): Handle LDPT_REGISTER_CLAIM_FILE_HOOK_V2.

include/plugin-api.h

@@ -260,6 +260,13 @@ enum ld_plugin_status
 (*ld_plugin_claim_file_handler) (
   const struct ld_plugin_input_file *file, int *claimed);
 
+/* The plugin library's "claim file" handler, version 2.  */
+
+typedef
+enum ld_plugin_status
+(*ld_plugin_claim_file_handler_v2) (
+  const struct ld_plugin_input_file *file, int *claimed, int known_used);
+
 /* The plugin library's "all symbols read" handler.  */
 
 typedef
@@ -278,6 +285,13 @@ typedef
 enum ld_plugin_status
 (*ld_plugin_register_claim_file) (ld_plugin_claim_file_handler handler);
 
+/* The linker's interface for registering the "claim file" handler,
+   version 2.  */
+
+typedef
+enum ld_plugin_status
+(*ld_plugin_register_claim_file_v2) (ld_plugin_claim_file_handler_v2 handler);
+
 /* The linker's interface for registering the "all symbols read" handler.  */
 
 typedef
@@ -553,6 +567,7 @@ enum ld_plugin_tag
   LDPT_GET_WRAP_SYMBOLS,
   LDPT_ADD_SYMBOLS_V2,
   LDPT_GET_API_VERSION,
+  LDPT_REGISTER_CLAIM_FILE_HOOK_V2
 };
 
 /* The plugin transfer vector.  */
@@ -565,6 +580,7 @@ struct ld_plugin_tv
     int tv_val;
     const char *tv_string;
     ld_plugin_register_claim_file tv_register_claim_file;
+    ld_plugin_register_claim_file_v2 tv_register_claim_file_v2;
     ld_plugin_register_all_symbols_read tv_register_all_symbols_read;
     ld_plugin_register_cleanup tv_register_cleanup;
     ld_plugin_add_symbols tv_add_symbols;

lto-plugin/lto-plugin.c

@@ -173,6 +173,7 @@ static pthread_mutex_t plugin_lock;
 
 static char *arguments_file_name;
 static ld_plugin_register_claim_file register_claim_file;
+static ld_plugin_register_claim_file_v2 register_claim_file_v2;
 static ld_plugin_register_all_symbols_read register_all_symbols_read;
 static ld_plugin_get_symbols get_symbols, get_symbols_v2, get_symbols_v3;
 static ld_plugin_register_cleanup register_cleanup;
@@ -1191,10 +1192,15 @@ process_offload_section (void *data, const char *name, off_t offset, off_t len)
 }
 
 /* Callback used by a linker to check if the plugin will claim FILE. Writes
-   the result in CLAIMED. */
+   the result in CLAIMED.  If KNOWN_USED, the object is known by the linker
+   to be used, or an older API version is in use that does not provide that
+   information; otherwise, the linker is only determining whether this is
+   a plugin object and it should not be registered as having offload data if
+   not claimed by the plugin.  */
 
 static enum ld_plugin_status
-claim_file_handler (const struct ld_plugin_input_file *file, int *claimed)
+claim_file_handler_v2 (const struct ld_plugin_input_file *file, int *claimed,
+		       int known_used)
 {
   enum ld_plugin_status status;
   struct plugin_objfile obj;
@@ -1307,7 +1313,7 @@ claim_file_handler (const struct ld_plugin_input_file *file, int *claimed)
   if (*claimed && !obj.offload && offload_files_last_lto == NULL)
     offload_files_last_lto = offload_files_last;
 
-  if (obj.offload)
+  if (obj.offload && (known_used || obj.found > 0))
     {
       /* Add file to the list.  The order must be exactly the same as the final
 	 order after recompilation and linking, otherwise host and target tables
@@ -1372,6 +1378,15 @@ claim_file_handler (const struct ld_plugin_input_file *file, int *claimed)
   return LDPS_OK;
 }
 
+/* Callback used by a linker to check if the plugin will claim FILE. Writes
+   the result in CLAIMED. */
+
+static enum ld_plugin_status
+claim_file_handler (const struct ld_plugin_input_file *file, int *claimed)
+{
+  return claim_file_handler_v2 (file, claimed, true);
+}
+
 /* Parse the plugin options. */
 
 static void
@@ -1496,6 +1511,9 @@ onload (struct ld_plugin_tv *tv)
 	case LDPT_REGISTER_CLAIM_FILE_HOOK:
 	  register_claim_file = p->tv_u.tv_register_claim_file;
 	  break;
+	case LDPT_REGISTER_CLAIM_FILE_HOOK_V2:
+	  register_claim_file_v2 = p->tv_u.tv_register_claim_file_v2;
+	  break;
 	case LDPT_ADD_SYMBOLS_V2:
 	  add_symbols_v2 = p->tv_u.tv_add_symbols;
 	  break;
@@ -1555,6 +1573,13 @@ onload (struct ld_plugin_tv *tv)
   check (status == LDPS_OK, LDPL_FATAL,
 	 "could not register the claim_file callback");
 
+  if (register_claim_file_v2)
+    {
+      status = register_claim_file_v2 (claim_file_handler_v2);
+      check (status == LDPS_OK, LDPL_FATAL,
+	     "could not register the claim_file_v2 callback");
+    }
+
   if (register_cleanup)
     {
       status = register_cleanup (cleanup_handler);