[PATCH] PR ld/21903: Treat common symbol as undefined for --no-define-common

["H.J. Lu" <hjl dot tools at gmail dot com>]

When --no-define-common is used to build shared library, treat common
symbol as undefined so that common symbols that are referenced from a
shared library to be assigned addresses only in the main program.  This
eliminates the unused duplicate space in the shared library, and also
prevents any possible confusion over resolving to the wrong duplicate
when there are many dynamic modules with specialized search paths for
runtime symbol resolution.

--no-define-common is only allowed when building a shared library.

OK for master?

H.J.
---
bfd/

	PR ld/21903:
	* elflink.c (elf_link_add_object_symbols): Treat common symbol
	as undefined for --no-define-common.

include/

	PR ld/21903:
	* bfdlink.h (bfd_link_info): Add inhibit_common_definition.

ld/

	PR ld/21903:
	* ld.h (command_line): Remove inhibit_common_definition.
	* ldgram.y: Replace command_line.inhibit_common_definition with
	link_info.inhibit_common_definition.
	* ldlang.c (lang_common): Likewise.
	* lexsup.c (parse_args): Likewise.
	* ldmain.c (main): Only allow --no-define-common with -shared.
	* testsuite/ld-elf/pr21903.s: New file.
	* testsuite/ld-elf/pr21903a.d: Likewise.
	* testsuite/ld-elf/pr21903b.d: Likewise.
	* testsuite/ld-elf/pr21903c.d: Likewise.
	* testsuite/ld-elf/pr21903d.d: Likewise.
	* testsuite/ld-elf/pr21903e.d: Likewise.
---
 bfd/elflink.c                  |  5 +++++
 include/bfdlink.h              |  3 +++
 ld/ld.h                        |  3 ---
 ld/ldgram.y                    |  2 +-
 ld/ldlang.c                    |  2 +-
 ld/ldmain.c                    |  3 +++
 ld/lexsup.c                    |  2 +-
 ld/testsuite/ld-elf/pr21903.s  | 15 +++++++++++++++
 ld/testsuite/ld-elf/pr21903a.d |  8 ++++++++
 ld/testsuite/ld-elf/pr21903b.d |  8 ++++++++
 ld/testsuite/ld-elf/pr21903c.d |  3 +++
 ld/testsuite/ld-elf/pr21903d.d |  4 ++++
 ld/testsuite/ld-elf/pr21903e.d |  3 +++
 13 files changed, 55 insertions(+), 6 deletions(-)
 create mode 100644 ld/testsuite/ld-elf/pr21903.s
 create mode 100644 ld/testsuite/ld-elf/pr21903a.d
 create mode 100644 ld/testsuite/ld-elf/pr21903b.d
 create mode 100644 ld/testsuite/ld-elf/pr21903c.d
 create mode 100644 ld/testsuite/ld-elf/pr21903d.d
 create mode 100644 ld/testsuite/ld-elf/pr21903e.d

diff --git a/bfd/elflink.c b/bfd/elflink.c
index eff53acbbe..0cc5f871db 100644
--- a/bfd/elflink.c
+++ b/bfd/elflink.c
@@ -4250,6 +4250,11 @@ error_free_dyn:
 
       override = FALSE;
 
+      /* Treat common symbol as undefined for --no-define-common.  */
+      if (isym->st_shndx == SHN_COMMON
+	  && info->inhibit_common_definition)
+	isym->st_shndx = SHN_UNDEF;
+
       flags = BSF_NO_FLAGS;
       sec = NULL;
       value = isym->st_value;
diff --git a/include/bfdlink.h b/include/bfdlink.h
index e7c7836f7f..2370c0d45a 100644
--- a/include/bfdlink.h
+++ b/include/bfdlink.h
@@ -489,6 +489,9 @@ struct bfd_link_info
   /* TRUE if generate a 1-byte NOP as suffix for x86 call instruction.  */
   unsigned int call_nop_as_suffix : 1;
 
+  /* TRUE if common symbols should be treated as undefined.  */
+  unsigned int inhibit_common_definition : 1;
+
   /* The 1-byte NOP for x86 call instruction.  */
   char call_nop_byte;
 
diff --git a/ld/ld.h b/ld/ld.h
index 162e156f08..c6fa1247f0 100644
--- a/ld/ld.h
+++ b/ld/ld.h
@@ -132,9 +132,6 @@ typedef struct
   /* 1 => assign space to common symbols even if `relocatable_output'.  */
   bfd_boolean force_common_definition;
 
-  /* 1 => do not assign addresses to common symbols.  */
-  bfd_boolean inhibit_common_definition;
-
   /* If TRUE, build MIPS embedded PIC relocation tables in the output
      file.  */
   bfd_boolean embedded_relocs;
diff --git a/ld/ldgram.y b/ld/ldgram.y
index 771d990a5c..e2998f1553 100644
--- a/ld/ldgram.y
+++ b/ld/ldgram.y
@@ -339,7 +339,7 @@ ifile_p1:
 	|	FORCE_GROUP_ALLOCATION
 		{ command_line.force_group_allocation = TRUE ; }
 	|	INHIBIT_COMMON_ALLOCATION
-		{ command_line.inhibit_common_definition = TRUE ; }
+		{ link_info.inhibit_common_definition = TRUE ; }
 	|	INPUT '(' input_list ')'
 	|	GROUP
 		  { lang_enter_group (); }
diff --git a/ld/ldlang.c b/ld/ldlang.c
index b8b214dfdb..196b2ccc72 100644
--- a/ld/ldlang.c
+++ b/ld/ldlang.c
@@ -6260,7 +6260,7 @@ lang_check (void)
 static void
 lang_common (void)
 {
-  if (command_line.inhibit_common_definition)
+  if (link_info.inhibit_common_definition)
     return;
   if (bfd_link_relocatable (&link_info)
       && !command_line.force_common_definition)
diff --git a/ld/ldmain.c b/ld/ldmain.c
index 5d1a3f46f5..cb1e2d158b 100644
--- a/ld/ldmain.c
+++ b/ld/ldmain.c
@@ -395,6 +395,9 @@ main (int argc, char **argv)
   if (argc == 2 && version_printed)
     xexit (0);
 
+  if (link_info.inhibit_common_definition && !bfd_link_dll (&link_info))
+    einfo (_("%P%F: --no-define-common may not be used without -shared\n"));
+
   if (!lang_has_input_file)
     {
       if (version_printed || command_line.print_output_format)
diff --git a/ld/lexsup.c b/ld/lexsup.c
index 08106bcc1a..effa277b16 100644
--- a/ld/lexsup.c
+++ b/ld/lexsup.c
@@ -908,7 +908,7 @@ parse_args (unsigned argc, char **argv)
 	  input_flags.dynamic = FALSE;
 	  break;
 	case OPTION_NO_DEFINE_COMMON:
-	  command_line.inhibit_common_definition = TRUE;
+	  link_info.inhibit_common_definition = TRUE;
 	  break;
 	case OPTION_NO_DEMANGLE:
 	  demangling = FALSE;
diff --git a/ld/testsuite/ld-elf/pr21903.s b/ld/testsuite/ld-elf/pr21903.s
new file mode 100644
index 0000000000..9dbf96c62e
--- /dev/null
+++ b/ld/testsuite/ld-elf/pr21903.s
@@ -0,0 +1,15 @@
+	.text
+	.global start	/* Used by SH targets.  */
+start:
+	.global _start
+_start:
+	.global __start
+__start:
+	.global main	/* Used by HPPA targets.  */
+main:
+	.dc.a foo
+	.ifdef	HPUX
+foo	.comm	4
+	.else
+	.comm	foo, 4, 4
+	.endif
diff --git a/ld/testsuite/ld-elf/pr21903a.d b/ld/testsuite/ld-elf/pr21903a.d
new file mode 100644
index 0000000000..020c5612e9
--- /dev/null
+++ b/ld/testsuite/ld-elf/pr21903a.d
@@ -0,0 +1,8 @@
+#source: pr21903.s
+#ld: -shared --no-define-common
+#readelf: --dyn-syms
+#target: *-*-linux* *-*-gnu*
+
+#...
+.*: 0+0 +0 +OBJECT +GLOBAL +DEFAULT +UND foo
+#pass
diff --git a/ld/testsuite/ld-elf/pr21903b.d b/ld/testsuite/ld-elf/pr21903b.d
new file mode 100644
index 0000000000..decd4f3e27
--- /dev/null
+++ b/ld/testsuite/ld-elf/pr21903b.d
@@ -0,0 +1,8 @@
+#source: pr21903.s
+#ld: -shared
+#readelf: --dyn-syms
+#target: *-*-linux* *-*-gnu*
+
+#...
+.*: [0-9a-f]+ +4 +OBJECT +GLOBAL +DEFAULT +[0-9]+ foo
+#pass
diff --git a/ld/testsuite/ld-elf/pr21903c.d b/ld/testsuite/ld-elf/pr21903c.d
new file mode 100644
index 0000000000..d3910ec79b
--- /dev/null
+++ b/ld/testsuite/ld-elf/pr21903c.d
@@ -0,0 +1,3 @@
+#source: pr21903.s
+#ld: --no-define-common
+#error: --no-define-common may not be used without -shared
diff --git a/ld/testsuite/ld-elf/pr21903d.d b/ld/testsuite/ld-elf/pr21903d.d
new file mode 100644
index 0000000000..ec729007d1
--- /dev/null
+++ b/ld/testsuite/ld-elf/pr21903d.d
@@ -0,0 +1,4 @@
+#source: pr21903.s
+#ld: --no-define-common -pie
+#target: *-*-linux* *-*-gnu*
+#error: --no-define-common may not be used without -shared
diff --git a/ld/testsuite/ld-elf/pr21903e.d b/ld/testsuite/ld-elf/pr21903e.d
new file mode 100644
index 0000000000..894c595c43
--- /dev/null
+++ b/ld/testsuite/ld-elf/pr21903e.d
@@ -0,0 +1,3 @@
+#source: pr21903.s
+#ld: -r --no-define-common
+#error: --no-define-common may not be used without -shared
-- 
2.13.3