PR 22843: ld, gold: Add --dependency-file option.users/roland/ld-depfile

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.

16 files changed, 173 insertions, 3 deletions

diff --git a/gold/ChangeLog b/gold/ChangeLog
index f4679f9a646..025a12a11c9 100644
--- a/gold/ChangeLog
+++ b/gold/ChangeLog
@@ -1,3 +1,16 @@
+2020-06-22  Roland McGrath  <mcgrathr@google.com>
+
+	PR 22843
+	* 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.
+
 2020-06-18  Fangrui Song  <i@maskray.me>
 
 	PR gold/26039
diff --git a/gold/fileread.cc b/gold/fileread.cc
index bebe0aba8d0..5f8ef62ee6f 100644
--- a/gold/fileread.cc
+++ b/gold/fileread.cc
@@ -124,6 +124,7 @@ static Initialize_lock file_counts_initialize_lock(&file_counts_lock);
 unsigned long long File_read::total_mapped_bytes;
 unsigned long long File_read::current_mapped_bytes;
 unsigned long long File_read::maximum_mapped_bytes;
+std::vector<std::string> File_read::files_read;
 
 // Class File_read::View.
 
@@ -211,6 +212,8 @@ File_read::open(const Task* task, const std::string& name)
       gold_debug(DEBUG_FILES, "Attempt to open %s succeeded",
 		 this->name_.c_str());
       this->token_.add_writer(task);
+      Hold_optional_lock hl(file_counts_lock);
+      record_file_read(this->name_);
     }
 
   return this->descriptor_ >= 0;
@@ -1138,4 +1141,31 @@ Input_file::open_binary(const Task* task, const std::string& name)
 			  binary_to_elf.converted_size());
 }
 
+void
+File_read::record_file_read(const std::string& name)
+{
+  File_read::files_read.push_back(name);
+}
+
+void
+File_read::write_dependency_file(const char* dependency_file_name,
+                                 const char* output_file_name)
+{
+  FILE *depfile = fopen(dependency_file_name, "w");
+
+  fprintf(depfile, "%s:", output_file_name);
+  for (std::vector<std::string>::const_iterator it = files_read.begin();
+       it != files_read.end();
+       ++it)
+    fprintf(depfile, " \\\n  %s", it->c_str());
+  fprintf(depfile, "\n");
+
+  for (std::vector<std::string>::const_iterator it = files_read.begin();
+       it != files_read.end();
+       ++it)
+    fprintf(depfile, "\n%s:\n", it->c_str());
+
+  fclose(depfile);
+}
+
 } // End namespace gold.
diff --git a/gold/fileread.h b/gold/fileread.h
index cf92367c2ca..4a04ed9fb9c 100644
--- a/gold/fileread.h
+++ b/gold/fileread.h
@@ -207,6 +207,15 @@ class File_read
   static void
   print_stats();
 
+  // Write the dependency file listing all files read.
+  static void
+  write_dependency_file(const char* dependency_file_name,
+                        const char* output_file_name);
+
+  // Record that a file was read.  File_read::open does this.
+  static void
+  record_file_read(const std::string& name);
+
   // Return the open file descriptor (for plugins).
   int
   descriptor()
@@ -214,7 +223,7 @@ class File_read
     this->reopen_descriptor();
     return this->descriptor_;
   }
-  
+
   // Return the file last modification time.  Calls gold_fatal if the stat
   // system call failed.
   Timespec
@@ -247,6 +256,9 @@ class File_read
   // --stats.
   static unsigned long long maximum_mapped_bytes;
 
+  // Set of names of all files read.
+  static std::vector<std::string> files_read;
+
   // A view into the file.
   class View
   {
diff --git a/gold/layout.cc b/gold/layout.cc
index 0c7be85240e..b8eaa3d2df5 100644
--- a/gold/layout.cc
+++ b/gold/layout.cc
@@ -2922,6 +2922,8 @@ Layout::read_layout_from_file()
     gold_fatal(_("unable to open --section-ordering-file file %s: %s"),
 	       filename, strerror(errno));
 
+  File_read::record_file_read(filename);
+
   std::getline(in, line);   // this chops off the trailing \n, if any
   unsigned int position = 1;
   this->set_section_ordering_specified();
@@ -6156,6 +6158,10 @@ Close_task_runner::run(Workqueue*, const Task*)
   if (this->options_->oformat_enum() != General_options::OBJECT_FORMAT_ELF)
     this->layout_->write_binary(this->of_);
 
+  if (this->options_->dependency_file())
+    File_read::write_dependency_file(this->options_->dependency_file(),
+                                     this->options_->output_file_name());
+
   this->of_->close();
 }
 
diff --git a/gold/options.h b/gold/options.h
index f0e9fbddcd5..b9b83aefae2 100644
--- a/gold/options.h
+++ b/gold/options.h
@@ -472,7 +472,7 @@ struct Struct_special : public Struct_var
   options::String_set::const_iterator					  \
   varname__##_end() const						  \
   { return this->varname__##_.value.end(); }                              \
-                                                                          \
+									  \
   options::String_set::size_type                                          \
   varname__##_size() const                                                \
   { return this->varname__##_.value.size(); }                             \
@@ -800,6 +800,10 @@ class General_options
 	      N_("Do not demangle C++ symbols in log messages"),
 	      NULL);
 
+  DEFINE_string(dependency_file, options::TWO_DASHES, '\0', NULL,
+		N_("Write a dependency file listing all files read"),
+		N_("FILE"));
+
   DEFINE_bool(detect_odr_violations, options::TWO_DASHES, '\0', false,
 	      N_("Look for violations of the C++ One Definition Rule"),
 	      N_("Do not look for violations of the C++ One Definition Rule"));
diff --git a/ld/ChangeLog b/ld/ChangeLog
index b67cd518a6a..ad441fc9a20 100644
--- a/ld/ChangeLog
+++ b/ld/ChangeLog
@@ -1,3 +1,21 @@
+2020-06-22  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.
+
 2020-06-22  Nelson Chu  <nelson.chu@sifive.com>
 
 	* testsuite/ld-riscv-elf/attr-merge-priv-spec-failed-01.d: Updated.
diff --git a/ld/NEWS b/ld/NEWS
index 6955937429b..4dd4f3c7528 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 71fd7812677..1790dc81a66 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 ecdbf775eb3..40b042de9b9 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 8f2167e8895..6fa09cfe6f1 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 f3de2c2356a..acd712376a8 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;
 
@@ -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 7868dca3499..5ea083ebeb3 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 d34d30ae337..8c427f04b14 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)
 {
@@ -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 0f05821d1e8..ac7db5720d5 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 65a94531852..5288255ccc0 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,
@@ -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;
 	}
     }
 
diff --git a/ld/pe-dll.c b/ld/pe-dll.c
index f72b6583411..3e8fe1be9b3 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))
     {