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.

1 files changed, 15 insertions, 0 deletions

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}