Properly handle uninitialized common symbol

Uninitialized common symbol behavior in executables is target and linker
dependent.  default_binds_local_p_3 is made public and updated to take an
argument to indicate if the linker can guarantee that an uninitialized
common symbol in the executable will still be defined (through COPY
relocation) in the executable.  If common symbol is local to executable,
default_binds_local_p_3 will treat non-external variable as defined
locally.  default_binds_local_p_2 is changed to treat common symbol as
local for non-PIE binaries.

For i386, common symbol is local only for non-PIE binaries.  For x86-64,
common symbol is local only for non-PIE binaries or linker supports copy
reloc in PIE binaries.  If a target treats common symbol as local only
for non-PIE binaries, it can define TARGET_BINDS_LOCAL_P as
default_binds_local_p_2.

gcc/

	PR target/65780
	* output.h (default_binds_local_p_3): New.
	* varasm.c (default_binds_local_p_3): Make it public.  Take an
	argument to indicate if common symbol may be local.  If common
	symbol may be local, treat non-external variable as defined
	locally.
	(default_binds_local_p_2): Pass !flag_pic to default_binds_local_p_3.
	(default_binds_local_p_1): Pass false to default_binds_local_p_3.
	* config/i386/i386.c (ix86_binds_local_p): New.
	(TARGET_BINDS_LOCAL_P): Replace default_binds_local_p_2 with
	ix86_binds_local_p.

gcc/testsuite/

	PR target/65780
	* gcc.dg/pr65780-1.c: New test.
	* gcc.dg/pr65780-2.c: Likewise.
	* gcc.target/i386/pr32219-9.c: Likewise.
	* gcc.target/i386/pr32219-1.c (xxx): Make it initialized common
	symbol.
	* gcc.target/i386/pr64317.c (c): Initialize.

From-SVN: r222184

1 files changed, 23 insertions, 12 deletions

diff --git a/gcc/varasm.c b/gcc/varasm.c
index e644b1d..e8d996c 100644
--- a/gcc/varasm.c
+++ b/gcc/varasm.c
@@ -6809,9 +6809,13 @@ resolution_local_p (enum ld_plugin_symbol_resolution resolution)
 	  || resolution == LDPR_RESOLVED_EXEC);
 }
 
-static bool
+/* COMMON_LOCAL_P is true means that the linker can guarantee that an
+   uninitialized common symbol in the executable will still be defined
+   (through COPY relocation) in the executable.  */
+
+bool
 default_binds_local_p_3 (const_tree exp, bool shlib, bool weak_dominate,
-			 bool extern_protected_data)
+			 bool extern_protected_data, bool common_local_p)
 {
   /* A non-decl is an entry in the constant pool.  */
   if (!DECL_P (exp))
@@ -6836,7 +6840,16 @@ default_binds_local_p_3 (const_tree exp, bool shlib, bool weak_dominate,
      because dynamic linking might overwrite symbols
      in shared libraries.  */
   bool resolved_locally = false;
-  bool defined_locally = !DECL_EXTERNAL (exp);
+
+  bool uninited_common = (DECL_COMMON (exp)
+			  && (DECL_INITIAL (exp) == NULL
+			      || (!in_lto_p
+				  && DECL_INITIAL (exp) == error_mark_node)));
+
+  /* A non-external variable is defined locally only if it isn't
+     uninitialized COMMON variable or common_local_p is true.  */
+  bool defined_locally = (!DECL_EXTERNAL (exp)
+			  && (!uninited_common || common_local_p));
   if (symtab_node *node = symtab_node::get (exp))
     {
       if (node->in_other_partition)
@@ -6878,10 +6891,7 @@ default_binds_local_p_3 (const_tree exp, bool shlib, bool weak_dominate,
 
   /* Uninitialized COMMON variable may be unified with symbols
      resolved from other modules.  */
-  if (DECL_COMMON (exp)
-      && !resolved_locally
-      && (DECL_INITIAL (exp) == NULL
-	  || (!in_lto_p && DECL_INITIAL (exp) == error_mark_node)))
+  if (uninited_common && !resolved_locally)
     return false;
 
   /* Otherwise we're left with initialized (or non-common) global data
@@ -6895,21 +6905,22 @@ default_binds_local_p_3 (const_tree exp, bool shlib, bool weak_dominate,
 bool
 default_binds_local_p (const_tree exp)
 {
-  return default_binds_local_p_3 (exp, flag_shlib != 0, true, false);
+  return default_binds_local_p_3 (exp, flag_shlib != 0, true, false, false);
 }
 
-/* Similar to default_binds_local_p, but protected data may be
-   external.  */
+/* Similar to default_binds_local_p, but common symbol may be local.  */
+
 bool
 default_binds_local_p_2 (const_tree exp)
 {
-  return default_binds_local_p_3 (exp, flag_shlib != 0, true, true);
+  return default_binds_local_p_3 (exp, flag_shlib != 0, true, false,
+				  !flag_pic);
 }
 
 bool
 default_binds_local_p_1 (const_tree exp, int shlib)
 {
-  return default_binds_local_p_3 (exp, shlib != 0, false, false);
+  return default_binds_local_p_3 (exp, shlib != 0, false, false, false);
 }
 
 /* Return true when references to DECL must bind to current definition in