gold, ld: Implement -z start-stop-visibility=... option.

gold/
	Implement -z start-stop-visibility=... option.
	* options.h (class General_options): Handle -z start-stop-visibility=.
	(General_options::start_stop_visibility_enum): New public method.
	(General_options::set_start_stop_visibility_enum): New private method.
	(General_options::start_stop_visibility_enum_): New private member.
	* options.cc (General_options::General_options): Add initializer.
	(General_options::finalize): Set this->start_stop_visibility_enum_
	from string value.
	* layout.cc (Layout::define_section_symbols): Use option setting.

bfd/
	* elflink.c (bfd_elf_define_start_stop): Use start_stop_visibility
	field of bfd_link_info.

include/
	* bfdlink.h (struct bfd_link_info): New field start_stop_visibility.

ld/
	* NEWS: Mention -z start-stop-visibility=... option for ELF.
	* ld.texi (Options): Document -z start-stop-visibility=... option.
	* ldmain.c (main): Initialize link_info.start_stop_visibility.
	* emultempl/elf.em (gld${EMULATION_NAME}_handle_option):
	Parse -z start-stop-visibility=... option.

5 files changed, 41 insertions, 0 deletions

diff --git a/ld/ChangeLog b/ld/ChangeLog
index c6de044..6700e72 100644
--- a/ld/ChangeLog
+++ b/ld/ChangeLog
@@ -1,3 +1,11 @@
+2020-06-15  Roland McGrath  <mcgrathr@google.com>
+
+	* NEWS: Mention -z start-stop-visibility=... option for ELF.
+	* ld.texi (Options): Document -z start-stop-visibility=... option.
+	* ldmain.c (main): Initialize link_info.start_stop_visibility.
+	* emultempl/elf.em (gld${EMULATION_NAME}_handle_option):
+	Parse -z start-stop-visibility=... option.
+
 2020-06-15  Alan Modra  <amodra@gmail.com>
 
 	* testsuite/ld-scripts/include.exp: Don't load ld-lib.exp.
diff --git a/ld/NEWS b/ld/NEWS
index 485e1cf..6955937 100644
--- a/ld/NEWS
+++ b/ld/NEWS
@@ -25,6 +25,9 @@
   searched relative to the directory of the linker script before other search
   paths.
 
+* Add ELF linker command-line option `-z start-stop-visibility=...' to control
+  the visibility of synthetic `__start_SECNAME` and `__stop_SECNAME` symbols.
+
 Changes in 2.34:
 
 * The ld check for "PHDR segment not covered by LOAD segment" is more
diff --git a/ld/emultempl/elf.em b/ld/emultempl/elf.em
index c4979eb..c577e8b 100644
--- a/ld/emultempl/elf.em
+++ b/ld/emultempl/elf.em
@@ -749,6 +749,21 @@ fragment <<EOF
 	{
 	  link_info.flags_1 |= DF_1_GLOBAUDIT;
 	}
+      else if (CONST_STRNEQ (optarg, "start-stop-visibility="))
+	{
+	  if (strcmp (optarg, "start-stop-visibility=default") == 0)
+	    link_info.start_stop_visibility = STV_DEFAULT;
+	  else if (strcmp (optarg, "start-stop-visibility=internal") == 0)
+	    link_info.start_stop_visibility = STV_INTERNAL;
+	  else if (strcmp (optarg, "start-stop-visibility=hidden") == 0)
+	    link_info.start_stop_visibility = STV_HIDDEN;
+	  else if (strcmp (optarg, "start-stop-visibility=protected") == 0)
+	    link_info.start_stop_visibility = STV_PROTECTED;
+	  else
+	    einfo (_("%F%P: invalid visibility in \`-z %s'; "
+		     "must be default, internal, hidden, or protected"),
+		   optarg);
+	}
 EOF
 
 if test x"$GENERATE_SHLIB_SCRIPT" = xyes; then
diff --git a/ld/ld.texi b/ld/ld.texi
index bf474d4..b89c1a5 100644
--- a/ld/ld.texi
+++ b/ld/ld.texi
@@ -1373,6 +1373,19 @@ Specify a stack size for an ELF @code{PT_GNU_STACK} segment.
 Specifying zero will override any default non-zero sized
 @code{PT_GNU_STACK} segment creation.
 
+@item start-stop-visibility=@var{value}
+@cindex visibility
+@cindex ELF symbol visibility
+Specify the ELF symbol visibility for synthesized
+@code{__start_SECNAME} and @code{__stop_SECNAME} symbols (@pxref{Input
+Section Example}).  @var{value} must be exactly @samp{default},
+@samp{internal}, @samp{hidden}, or @samp{protected}.  If no @samp{-z
+start-stop-visibility} option is given, @samp{protected} is used for
+compatibility with historical practice.  However, it's highly
+recommended to use @samp{-z start-stop-visibility=hidden} in new
+programs and shared libraries so that these symbols are not exported
+between shared objects, which is not usually what's intended.
+
 @item text
 @itemx notext
 @itemx textoff
diff --git a/ld/ldmain.c b/ld/ldmain.c
index e2c559e..b0ce69f 100644
--- a/ld/ldmain.c
+++ b/ld/ldmain.c
@@ -27,6 +27,7 @@
 #include "bfdlink.h"
 #include "ctf-api.h"
 #include "filenames.h"
+#include "elf/common.h"
 
 #include "ld.h"
 #include "ldmain.h"
@@ -307,6 +308,7 @@ main (int argc, char **argv)
 #ifdef DEFAULT_NEW_DTAGS
   link_info.new_dtags = DEFAULT_NEW_DTAGS;
 #endif
+  link_info.start_stop_visibility = STV_PROTECTED;
 
   ldfile_add_arch ("");
   emulation = get_emulation (argc, argv);