PR 22843: ld, gold: Add --dependency-file option.

gold/
	* options.h (class General_options): Add --dependency-file option.
	* fileread.cc (File_read::files_read): New static variable.
	(File_read::open): Add the file to the files_read list.
	(File_read::record_file_read): New static member function.
	(File_read::write_dependency_file): New static member function.
	* fileread.h (class File_read): Declare them.
	* layout.cc (Layout::read_layout_from_file): Call record_file_read.
	(Close_task_runner::run): Call write_dependency_file if
	--dependency-file was passed.

ld/
	* NEWS: Note --dependency-file.
	* ld.texi (Options): Document --dependency-file.
	* ldlex.h (enum option_values): Add OPTION_DEPENDENCY_FILE.
	* ld.h (ld_config_type): New member dependency_file.
	* lexsup.c (ld_options, parse_args): Parse --dependency-file.
	* ldmain.c (struct dependency_file): New type.
	(dependency_files, dependency_files_tail): New static variables.
	(track_dependency_files): New function.
	(write_dependency_file): New function.
	(main): Call it when --dependency-file was passed.
	* ldfile.c (ldfile_try_open_bfd): Call track_dependency_files.
	(ldfile_open_command_file_1): Likewise.
	* ldelf.c (ldelf_try_needed): Likewise.
	* pe-dll.c (pe_implied_import_dll): Likewise.

11 files changed, 127 insertions, 22 deletions

diff --git a/ld/ChangeLog b/ld/ChangeLog
index a2e3f62..7917956 100644
--- a/ld/ChangeLog
+++ b/ld/ChangeLog
@@ -1,3 +1,21 @@
+2020-06-23  Roland McGrath  <mcgrathr@google.com>
+
+	PR 22843
+	* NEWS: Note --dependency-file.
+	* ld.texi (Options): Document --dependency-file.
+	* ldlex.h (enum option_values): Add OPTION_DEPENDENCY_FILE.
+	* ld.h (ld_config_type): New member dependency_file.
+	* lexsup.c (ld_options, parse_args): Parse --dependency-file.
+	* ldmain.c (struct dependency_file): New type.
+	(dependency_files, dependency_files_tail): New static variables.
+	(track_dependency_files): New function.
+	(write_dependency_file): New function.
+	(main): Call it when --dependency-file was passed.
+	* ldfile.c (ldfile_try_open_bfd): Call track_dependency_files.
+	(ldfile_open_command_file_1): Likewise.
+	* ldelf.c (ldelf_try_needed): Likewise.
+	* pe-dll.c (pe_implied_import_dll): Likewise.
+
 2020-06-23  Alan Modra  <amodra@gmail.com>
 
 	PR 26150
diff --git a/ld/NEWS b/ld/NEWS
index 6955937..4dd4f3c 100644
--- a/ld/NEWS
+++ b/ld/NEWS
@@ -28,6 +28,10 @@
 * Add ELF linker command-line option `-z start-stop-visibility=...' to control
   the visibility of synthetic `__start_SECNAME` and `__stop_SECNAME` symbols.
 
+* Add command-line option --dependency-file to write a Make-style dependency
+  file listing the input files consulted by the linker, like the files written
+  by the compiler's -M -MP options.
+
 Changes in 2.34:
 
 * The ld check for "PHDR segment not covered by LOAD segment" is more
diff --git a/ld/ld.h b/ld/ld.h
index 71fd781..1790dc8 100644
--- a/ld/ld.h
+++ b/ld/ld.h
@@ -286,6 +286,8 @@ typedef struct
   char *map_filename;
   FILE *map_file;
 
+  char *dependency_file;
+
   unsigned int split_by_reloc;
   bfd_size_type split_by_file;
 
diff --git a/ld/ld.texi b/ld/ld.texi
index ecdbf77..40b042d 100644
--- a/ld/ld.texi
+++ b/ld/ld.texi
@@ -893,6 +893,21 @@ Use @var{output} as the name for the program produced by @command{ld}; if this
 option is not specified, the name @file{a.out} is used by default.  The
 script command @code{OUTPUT} can also specify the output file name.
 
+@kindex --dependency-file=@var{depfile}
+@cindex dependency file
+@item --dependency-file=@var{depfile}
+Write a @dfn{dependency file} to @var{depfile}.  This file contains a rule
+suitable for @code{make} describing the output file and all the input files
+that were read to produce it.  The output is similar to the compiler's
+output with @samp{-M -MP} (@pxref{Preprocessor Options,, Options
+Controlling the Preprocessor, gcc.info, Using the GNU Compiler
+Collection}).  Note that there is no option like the compiler's @samp{-MM},
+to exclude ``system files'' (which is not a well-specified concept in the
+linker, unlike ``system headers'' in the compiler).  So the output from
+@samp{--dependency-file} is always specific to the exact state of the
+installation where it was produced, and should not be copied into
+distributed makefiles without careful editing.
+
 @kindex -O @var{level}
 @cindex generating optimized output
 @item -O @var{level}
diff --git a/ld/ldelf.c b/ld/ldelf.c
index 8f2167e..6fa09cf 100644
--- a/ld/ldelf.c
+++ b/ld/ldelf.c
@@ -262,6 +262,8 @@ ldelf_try_needed (struct dt_needed *needed, int force, int is_linux)
       return FALSE;
     }
 
+  track_dependency_files (name);
+
   /* Linker needs to decompress sections.  */
   abfd->flags |= BFD_DECOMPRESS;
 
@@ -1065,7 +1067,7 @@ ldelf_after_open (int use_libpath, int native, int is_linux, int is_freebsd,
 	}
       return;
     }
-  
+
   if (!link_info.traditional_format)
     {
       bfd *elfbfd = NULL;
diff --git a/ld/ldfile.c b/ld/ldfile.c
index f3de2c2..e39170b 100644
--- a/ld/ldfile.c
+++ b/ld/ldfile.c
@@ -142,6 +142,8 @@ ldfile_try_open_bfd (const char *attempt,
       return FALSE;
     }
 
+  track_dependency_files (attempt);
+
   /* Linker needs to decompress sections.  */
   entry->the_bfd->flags |= BFD_DECOMPRESS;
 
@@ -416,21 +418,21 @@ ldfile_open_file (lang_input_statement_type *entry)
       bfd_boolean found = FALSE;
 
       /* If extra_search_path is set, entry->filename is a relative path.
-         Search the directory of the current linker script before searching
-         other paths. */
+	 Search the directory of the current linker script before searching
+	 other paths. */
       if (entry->extra_search_path)
-        {
-          char *path = concat (entry->extra_search_path, slash, entry->filename,
-                               (const char *)0);
-          if (ldfile_try_open_bfd (path, entry))
-            {
-              entry->filename = path;
-              entry->flags.search_dirs = FALSE;
-              return;
-            }
+	{
+	  char *path = concat (entry->extra_search_path, slash, entry->filename,
+			       (const char *)0);
+	  if (ldfile_try_open_bfd (path, entry))
+	    {
+	      entry->filename = path;
+	      entry->flags.search_dirs = FALSE;
+	      return;
+	    }
 
 	  free (path);
-        }
+	}
 
       /* Try to open <filename><suffix> or lib<filename><suffix>.a.  */
       for (arch = search_arch_head; arch != NULL; arch = arch->next)
@@ -675,6 +677,8 @@ ldfile_open_command_file_1 (const char *name, enum script_open_style open_how)
       return;
     }
 
+  track_dependency_files (name);
+
   lex_push_file (ldlex_input_stack, name, sysrooted);
 
   lineno = 1;
diff --git a/ld/ldlex.h b/ld/ldlex.h
index 7868dca..5ea083e 100644
--- a/ld/ldlex.h
+++ b/ld/ldlex.h
@@ -154,6 +154,7 @@ enum option_values
   OPTION_NO_PRINT_MAP_DISCARDED,
   OPTION_NON_CONTIGUOUS_REGIONS,
   OPTION_NON_CONTIGUOUS_REGIONS_WARNINGS,
+  OPTION_DEPENDENCY_FILE,
 };
 
 /* The initial parser states.  */
diff --git a/ld/ldmain.c b/ld/ldmain.c
index 94a745e..08be903 100644
--- a/ld/ldmain.c
+++ b/ld/ldmain.c
@@ -160,6 +160,53 @@ static bfd_error_handler_type default_bfd_error_handler;
 
 struct bfd_link_info link_info;
 
+struct dependency_file
+{
+  struct dependency_file *next;
+  char *name;
+};
+
+static struct dependency_file *dependency_files, *dependency_files_tail;
+
+void
+track_dependency_files (const char *filename)
+{
+  struct dependency_file *dep
+    = (struct dependency_file *) xmalloc (sizeof (*dep));
+  dep->name = xstrdup (filename);
+  dep->next = NULL;
+  if (dependency_files == NULL)
+    dependency_files = dep;
+  else
+    dependency_files_tail->next = dep;
+  dependency_files_tail = dep;
+}
+
+static void
+write_dependency_file (void)
+{
+  FILE *out;
+  struct dependency_file *dep;
+
+  out = fopen (config.dependency_file, FOPEN_WT);
+  if (out == NULL)
+    {
+      einfo (_("%F%P: cannot open dependency file %s: %E\n"),
+	     config.dependency_file);
+    }
+
+  fprintf (out, "%s:", output_filename);
+
+  for (dep = dependency_files; dep != NULL; dep = dep->next)
+    fprintf (out, " \\\n  %s", dep->name);
+
+  fprintf (out, "\n");
+  for (dep = dependency_files; dep != NULL; dep = dep->next)
+    fprintf (out, "\n%s:\n", dep->name);
+
+  fclose (out);
+}
+
 static void
 ld_cleanup (void)
 {
@@ -239,7 +286,7 @@ main (int argc, char **argv)
       /* is_sysrooted_pathname() relies on no trailing dirsep.  */
       if (ld_canon_sysroot_len > 0
 	  && IS_DIR_SEPARATOR (ld_canon_sysroot [ld_canon_sysroot_len - 1]))
-        ld_canon_sysroot [--ld_canon_sysroot_len] = '\0';
+	ld_canon_sysroot [--ld_canon_sysroot_len] = '\0';
     }
   else
     ld_canon_sysroot_len = -1;
@@ -481,6 +528,9 @@ main (int argc, char **argv)
   ldexp_finish ();
   lang_finish ();
 
+  if (config.dependency_file != NULL)
+    write_dependency_file ();
+
   /* Even if we're producing relocatable output, some non-fatal errors should
      be reported in the exit status.  (What non-fatal errors, if any, do we
      want to ignore for relocatable output?)  */
diff --git a/ld/ldmain.h b/ld/ldmain.h
index 0f05821..ac7db57 100644
--- a/ld/ldmain.h
+++ b/ld/ldmain.h
@@ -58,5 +58,6 @@ extern void add_ysym (const char *);
 extern void add_wrap (const char *);
 extern void add_ignoresym (struct bfd_link_info *, const char *);
 extern void add_keepsyms_file (const char *);
+extern void track_dependency_files (const char *);
 
 #endif
diff --git a/ld/lexsup.c b/ld/lexsup.c
index 65a9453..48c6eca 100644
--- a/ld/lexsup.c
+++ b/ld/lexsup.c
@@ -111,6 +111,8 @@ static const struct ld_option ld_options[] =
     'c', N_("FILE"), N_("Read MRI format linker script"), TWO_DASHES },
   { {"dc", no_argument, NULL, 'd'},
     'd', NULL, N_("Force common symbols to be defined"), ONE_DASH },
+  { {"dependency-file", required_argument, NULL, OPTION_DEPENDENCY_FILE},
+    '\0', N_("FILE"), N_("Write dependency file"), TWO_DASHES },
   { {"dp", no_argument, NULL, 'd'},
     '\0', NULL, NULL, ONE_DASH },
   { {"force-group-allocation", no_argument, NULL,
@@ -1441,7 +1443,7 @@ parse_args (unsigned argc, char **argv)
 	      = lang_new_vers_pattern (NULL, xstrdup (optarg), NULL,
 				       FALSE);
 	    lang_append_dynamic_list (&export_list, expr);
-          }
+	  }
 	  break;
 	case OPTION_EXPORT_DYNAMIC_SYMBOL_LIST:
 	  /* This option indicates a small script that only specifies
@@ -1631,6 +1633,10 @@ parse_args (unsigned argc, char **argv)
 	case OPTION_PRINT_MAP_DISCARDED:
 	  config.print_map_discarded = TRUE;
 	  break;
+
+	case OPTION_DEPENDENCY_FILE:
+	  config.dependency_file = optarg;
+	  break;
 	}
     }
 
@@ -1906,14 +1912,14 @@ elf_shlib_list_options (FILE *file)
     }
   fprintf (file, _("\
   -P AUDITLIB, --depaudit=AUDITLIB\n" "\
-                              Specify a library to use for auditing dependencies\n"));
+			      Specify a library to use for auditing dependencies\n"));
   fprintf (file, _("\
   -z combreloc                Merge dynamic relocs into one section and sort\n"));
   fprintf (file, _("\
   -z nocombreloc              Don't merge dynamic relocs into one section\n"));
   fprintf (file, _("\
   -z global                   Make symbols in DSO available for subsequently\n\
-                               loaded objects\n"));
+			       loaded objects\n"));
   fprintf (file, _("\
   -z initfirst                Mark DSO to be initialized first at runtime\n"));
   fprintf (file, _("\
@@ -1936,7 +1942,7 @@ elf_shlib_list_options (FILE *file)
   -z now                      Mark object non-lazy runtime binding\n"));
   fprintf (file, _("\
   -z origin                   Mark object requiring immediate $ORIGIN\n\
-                                processing at runtime\n"));
+				processing at runtime\n"));
 #if DEFAULT_LD_Z_RELRO
   fprintf (file, _("\
   -z relro                    Create RELRO program header (default)\n"));
@@ -1994,13 +2000,13 @@ elf_static_list_options (FILE *file)
   --build-id[=STYLE]          Generate build ID note\n"));
   fprintf (file, _("\
   --compress-debug-sections=[none|zlib|zlib-gnu|zlib-gabi]\n\
-                              Compress DWARF debug sections using zlib\n"));
+			      Compress DWARF debug sections using zlib\n"));
 #ifdef DEFAULT_FLAG_COMPRESS_DEBUG
   fprintf (file, _("\
-                               Default: zlib-gabi\n"));
+			       Default: zlib-gabi\n"));
 #else
   fprintf (file, _("\
-                               Default: none\n"));
+			       Default: none\n"));
 #endif
   fprintf (file, _("\
   -z common-page-size=SIZE    Set common page size to SIZE\n"));
@@ -2025,7 +2031,7 @@ elf_plt_unwind_list_options (FILE *file)
   --ld-generated-unwind-info  Generate exception handling info for PLT\n"));
   fprintf (file, _("\
   --no-ld-generated-unwind-info\n\
-                              Don't generate exception handling info for PLT\n"));
+			      Don't generate exception handling info for PLT\n"));
 }
 
 static void
diff --git a/ld/pe-dll.c b/ld/pe-dll.c
index f72b658..3e8fe1b 100644
--- a/ld/pe-dll.c
+++ b/ld/pe-dll.c
@@ -3344,6 +3344,8 @@ pe_implied_import_dll (const char *filename)
       return FALSE;
     }
 
+  track_dependency_files (filename);
+
   /* PEI dlls seem to be bfd_objects.  */
   if (!bfd_check_format (dll, bfd_object))
     {