That supports skipping of an object file (LDPS_NO_SYMS). The API will be used 
by mold
and is there for some time in linkers.

Patch can bootstrap on x86_64-linux-gnu and survives regression tests.

Ready to be installed?
Thanks,
Martin

lto-plugin/ChangeLog:

        * lto-plugin.c (struct plugin_file_info): Add skip_file flag.
        (write_resolution): Write resolution only if get_symbols != 
LDPS_NO_SYMS.
        (all_symbols_read_handler): Ignore file if skip_file is true.
        (onload): Handle LDPT_GET_SYMBOLS_V3.
---
 lto-plugin/lto-plugin.c | 42 ++++++++++++++++++++++++++++++++++-------
 1 file changed, 35 insertions(+), 7 deletions(-)

diff --git a/lto-plugin/lto-plugin.c b/lto-plugin/lto-plugin.c
index 33d49571d0e..aa5eab48b9d 100644
--- a/lto-plugin/lto-plugin.c
+++ b/lto-plugin/lto-plugin.c
@@ -136,6 +136,7 @@ struct plugin_file_info
   void *handle;
   struct plugin_symtab symtab;
   struct plugin_symtab conflicts;
+  bool skip_file;
 };
 
 /* List item with name of the file with offloading.  */
@@ -159,7 +160,7 @@ enum symbol_style
 static char *arguments_file_name;
 static ld_plugin_register_claim_file register_claim_file;
 static ld_plugin_register_all_symbols_read register_all_symbols_read;
-static ld_plugin_get_symbols get_symbols, get_symbols_v2;
+static ld_plugin_get_symbols get_symbols, get_symbols_v2, get_symbols_v3;
 static ld_plugin_register_cleanup register_cleanup;
 static ld_plugin_add_input_file add_input_file;
 static ld_plugin_add_input_library add_input_library;
@@ -547,15 +548,13 @@ free_symtab (struct plugin_symtab *symtab)
 static void
 write_resolution (void)
 {
-  unsigned int i;
+  unsigned int i, included_files = 0;
   FILE *f;
 
   check (resolution_file, LDPL_FATAL, "resolution file not specified");
   f = fopen (resolution_file, "w");
   check (f, LDPL_FATAL, "could not open file");
 
-  fprintf (f, "%d\n", num_claimed_files);
-
   for (i = 0; i < num_claimed_files; i++)
     {
       struct plugin_file_info *info = &claimed_files[i];
@@ -563,13 +562,38 @@ write_resolution (void)
       struct ld_plugin_symbol *syms = symtab->syms;
 
       /* Version 2 of API supports IRONLY_EXP resolution that is
-         accepted by GCC-4.7 and newer.  */
-      if (get_symbols_v2)
+        accepted by GCC-4.7 and newer.
+        Version 3 can return LDPS_NO_SYMS that means the object
+        will not be used at all.  */
+      if (get_symbols_v3)
+       {
+         enum ld_plugin_status status
+           = get_symbols_v3 (info->handle, symtab->nsyms, syms);
+         if (status == LDPS_NO_SYMS)
+           {
+             info->skip_file = true;
+             continue;
+           }
+       }
+      else if (get_symbols_v2)
         get_symbols_v2 (info->handle, symtab->nsyms, syms);
       else
         get_symbols (info->handle, symtab->nsyms, syms);
 
+      ++included_files;
+
       finish_conflict_resolution (symtab, &info->conflicts);
+    }
+
+  fprintf (f, "%d\n", included_files);
+
+  for (i = 0; i < num_claimed_files; i++)
+    {
+      struct plugin_file_info *info = &claimed_files[i];
+      struct plugin_symtab *symtab = &info->symtab;
+
+      if (info->skip_file)
+       continue;
 
       fprintf (f, "%s %d\n", info->name, symtab->nsyms + 
info->conflicts.nsyms);
       dump_symtab (f, symtab);
@@ -832,7 +856,8 @@ all_symbols_read_handler (void)
     {
       struct plugin_file_info *info = &claimed_files[i];
 
-      *lto_arg_ptr++ = info->name;
+      if (!info->skip_file)
+       *lto_arg_ptr++ = info->name;
     }
 
   *lto_arg_ptr++ = NULL;
@@ -1409,6 +1434,9 @@ onload (struct ld_plugin_tv *tv)
        case LDPT_REGISTER_ALL_SYMBOLS_READ_HOOK:
          register_all_symbols_read = p->tv_u.tv_register_all_symbols_read;
          break;
+       case LDPT_GET_SYMBOLS_V3:
+         get_symbols_v3 = p->tv_u.tv_get_symbols;
+         break;
        case LDPT_GET_SYMBOLS_V2:
          get_symbols_v2 = p->tv_u.tv_get_symbols;
          break;
-- 
2.36.0

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