Implement the "retain" attribute

diff --git a/gcc/c-family/c-attribs.c b/gcc/c-family/c-attribs.c
index a3b2b3d58bd..72c0c61993e 100644
--- a/gcc/c-family/c-attribs.c
+++ b/gcc/c-family/c-attribs.c
@@ -155,6 +155,7 @@  static tree handle_designated_init_attribute (tree *, tree, tree, int, bool *);
 static tree handle_patchable_function_entry_attribute (tree *, tree, tree,
 						       int, bool *);
 static tree handle_copy_attribute (tree *, tree, tree, int, bool *);
+static tree handle_retain_attribute (tree *, tree, tree, int, bool *);
 
 /* Helper to define attribute exclusions.  */
 #define ATTR_EXCL(name, function, type, variable)	\
@@ -505,6 +506,8 @@  const struct attribute_spec c_common_attribute_table[] =
 			      handle_noinit_attribute, attr_noinit_exclusions },
   { "access",		      1, 3, false, true, true, false,
 			      handle_access_attribute, NULL },
+  { "retain",		      0, 0, true, false, false, false,
+			      handle_retain_attribute, NULL },
   { NULL,                     0, 0, false, false, false, false, NULL, NULL }
 };
 
@@ -2592,6 +2595,45 @@  handle_alias_ifunc_attribute (bool is_alias, tree *node, tree name, tree args,
 	       decl, is_alias ? "alias" : "ifunc");
     }
 
+  return NULL_TREE;
+}
+
+/* Handle a "retain" attribute; arguments as in
+   struct attribute_spec.handler.  */
+static tree
+handle_retain_attribute (tree *pnode ATTRIBUTE_UNUSED,
+			 tree   name,
+			 tree   args ATTRIBUTE_UNUSED,
+			 int    flags ATTRIBUTE_UNUSED,
+			 bool *no_add_attrs)
+{
+#if HAVE_GAS_SECTION_RETAIN
+  tree node = *pnode;
+
+  if (!targetm_common.have_named_sections)
+    {
+      warning (OPT_Wattributes, "%qE attribute not supported by this target",
+	       name);
+      *no_add_attrs = true;
+    }
+  else if (TREE_CODE (node) == FUNCTION_DECL
+	   || (VAR_P (node) && TREE_STATIC (node)))
+    {
+      TREE_USED (node) = 1;
+      DECL_PRESERVE_P (node) = 1;
+      DECL_RETAIN_P (node) = 1;
+      if (VAR_P (node))
+	DECL_READ_P (node) = 1;
+    }
+  else
+    {
+      warning (OPT_Wattributes, "%qE attribute ignored", name);
+      *no_add_attrs = true;
+    }
+#else
+  warning (OPT_Wattributes, "%qE attribute not supported by this target", name);
+  *no_add_attrs = true;
+#endif
 
   return NULL_TREE;
 }
diff --git a/gcc/config.in b/gcc/config.in
index 3657c46f349..343f2929588 100644
--- a/gcc/config.in
+++ b/gcc/config.in
@@ -1352,6 +1352,12 @@ 
 #endif
 
 
+/* Define if your assembler supports specifying the retain section flag. */
+#ifndef USED_FOR_TARGET
+#undef HAVE_GAS_SECTION_RETAIN
+#endif
+
+
 /* Define 0/1 if your assembler supports marking sections with SHF_MERGE flag.
    */
 #ifndef USED_FOR_TARGET
diff --git a/gcc/configure b/gcc/configure
index abff47d30eb..7abda5c13ab 100755
--- a/gcc/configure
+++ b/gcc/configure
@@ -24223,6 +24223,42 @@  cat >>confdefs.h <<_ACEOF
 _ACEOF
 
 
+# Test if the assembler supports the section flag 'R' for specifying a
+# section which should not be garbage collected by the linker.
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking assembler for section retain flag" >&5
+$as_echo_n "checking assembler for section retain flag... " >&6; }
+if ${gcc_cv_as_section_retain_r+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  gcc_cv_as_section_retain_r=no
+  if test x$gcc_cv_as != x; then
+    $as_echo '.section foo1,"aR"
+  .byte 0' > conftest.s
+    if { ac_try='$gcc_cv_as $gcc_cv_as_flags  -o conftest.o conftest.s >&5'
+  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
+  (eval $ac_try) 2>&5
+  ac_status=$?
+  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
+  test $ac_status = 0; }; }
+    then
+	gcc_cv_as_section_retain_r=yes
+    else
+      echo "configure: failed program was" >&5
+      cat conftest.s >&5
+    fi
+    rm -f conftest.o conftest.s
+  fi
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $gcc_cv_as_section_retain_r" >&5
+$as_echo "$gcc_cv_as_section_retain_r" >&6; }
+
+
+
+cat >>confdefs.h <<_ACEOF
+#define HAVE_GAS_SECTION_RETAIN `if test $gcc_cv_as_section_retain_r = yes; then echo 1; else echo 0; fi`
+_ACEOF
+
+
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking assembler for section merging support" >&5
 $as_echo_n "checking assembler for section merging support... " >&6; }
 if ${gcc_cv_as_shf_merge+:} false; then :
diff --git a/gcc/configure.ac b/gcc/configure.ac
index 26a5d8e3619..035df137cf6 100644
--- a/gcc/configure.ac
+++ b/gcc/configure.ac
@@ -3216,6 +3216,15 @@  AC_DEFINE_UNQUOTED(HAVE_GAS_SECTION_EXCLUDE,
   [`if test $gcc_cv_as_section_exclude_e = yes || test $gcc_cv_as_section_exclude_hash = yes; then echo 1; else echo 0; fi`],
 [Define if your assembler supports specifying the exclude section flag.])
 
+# Test if the assembler supports the section flag 'R' for specifying a
+# section which should not be garbage collected by the linker.
+gcc_GAS_CHECK_FEATURE([section retain flag], gcc_cv_as_section_retain_r,,,
+ [.section foo1,"aR"
+  .byte 0])
+AC_DEFINE_UNQUOTED(HAVE_GAS_SECTION_RETAIN,
+  [`if test $gcc_cv_as_section_retain_r = yes; then echo 1; else echo 0; fi`],
+[Define if your assembler supports specifying the retain section flag.])
+
 gcc_GAS_CHECK_FEATURE(section merging support, gcc_cv_as_shf_merge,
  [elf,2,12,0], [--fatal-warnings],
  [.section .rodata.str, "aMS", @progbits, 1])
diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
index 4a7c85822a7..25d49382fbb 100644
--- a/gcc/doc/extend.texi
+++ b/gcc/doc/extend.texi
@@ -3578,6 +3578,17 @@  diagnosed.  Because a pure function cannot have any observable side
 effects it does not make sense for such a function to return @code{void}.
 Declaring such a function is diagnosed.
 
+@item retain
+@cindex @code{retain} function attribute
+The @code{retain} attribute, attached to a function, means that function must
+not be garbage collected by the linker, even if it appears unused.
+
+The function is put in a new, unique section marked with the
+@code{SHF_GNU_RETAIN} flag.  This flag is a GNU extension to the ELF format.
+
+This attribute implies, and has the same restrictions as, the @code{used}
+attribute.
+
 @item returns_nonnull
 @cindex @code{returns_nonnull} function attribute
 The @code{returns_nonnull} attribute specifies that the function
@@ -7197,6 +7208,18 @@  been fixed in GCC 4.4 but the change can lead to differences in the
 structure layout.  See the documentation of
 @option{-Wpacked-bitfield-compat} for more information.
 
+@item retain
+@cindex @code{retain} variable attribute
+The @code{retain} attribute, attached to a variable with static storage, means
+that variable must not be garbage collected by the linker, even if it appears
+unused.
+
+The variable is put in a new, unique section marked with the
+@code{SHF_GNU_RETAIN} flag.  This flag is a GNU extension to the ELF format.
+
+This attribute implies, and has the same restrictions as, the @code{used}
+attribute.
+
 @item section ("@var{section-name}")
 @cindex @code{section} variable attribute
 Normally, the compiler places the objects it generates in sections like
diff --git a/gcc/doc/sourcebuild.texi b/gcc/doc/sourcebuild.texi
index 49316a5d0ff..85f13483d40 100644
--- a/gcc/doc/sourcebuild.texi
+++ b/gcc/doc/sourcebuild.texi
@@ -2551,6 +2551,9 @@  Target supports @option{-pie}, @option{-fpie} and @option{-fPIE}.
 @item rdynamic
 Target supports @option{-rdynamic}.
 
+@item retain
+Target supports the @code{retain} function/variable attribute.
+
 @item scalar_all_fma
 Target supports all four fused multiply-add optabs for both @code{float}
 and @code{double}.  These optabs are: @code{fma_optab}, @code{fms_optab},
diff --git a/gcc/output.h b/gcc/output.h
index eb253c50329..2a723969bd9 100644
--- a/gcc/output.h
+++ b/gcc/output.h
@@ -381,7 +381,8 @@  extern void no_asm_to_stream (FILE *);
 #define SECTION_COMMON   0x800000	/* contains common data */
 #define SECTION_RELRO	 0x1000000	/* data is readonly after relocation processing */
 #define SECTION_EXCLUDE  0x2000000	/* discarded by the linker */
-#define SECTION_MACH_DEP 0x4000000	/* subsequent bits reserved for target */
+#define SECTION_RETAIN   0x4000000	/* retained by the linker, SHF_GNU_RETAIN */
+#define SECTION_MACH_DEP 0x8000000	/* subsequent bits reserved for target */
 
 /* This SECTION_STYLE is used for unnamed sections that we can switch
    to using a special assembler directive.  */
diff --git a/gcc/testsuite/c-c++-common/attr-retain-1.c b/gcc/testsuite/c-c++-common/attr-retain-1.c
new file mode 100644
index 00000000000..c264eb654fc
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/attr-retain-1.c
@@ -0,0 +1,19 @@ 
+/* { dg-do compile } */
+/* { dg-require-effective-target retain } */
+/* { dg-final { scan-assembler "\\.section\t\[^,\]*retain0\[^,\]*,\"\\w+R" } } */
+/* { dg-final { scan-assembler "\\.section\t\[^,\]*retain1\[^,\]*,\"\\w+R" } } */
+/* { dg-final { scan-assembler "\\.section\t\[^,\]*retain2\[^,\]*,\"\\w+R" } } */
+/* { dg-final { scan-assembler "\\.section\t\[^,\]*retain3\[^,\]*,\"\\w+R" } } */
+/* { dg-final { scan-assembler "\\.section\t\[^,\]*sretain0\[^,\]*,\"\\w+R" } } */
+/* { dg-final { scan-assembler "\\.section\t\[^,\]*sretain1\[^,\]*,\"\\w+R" } } */
+/* { dg-final { scan-assembler "\\.section\t\[^,\]*sretain3\[^,\]*,\"\\w+R" } } */
+/* { dg-final { scan-assembler "\\.section\t\[^,\]*fretain0\[^,\]*,\"\\w+R" } } */
+/* { dg-final { scan-assembler "\\.section\t\[^,\]*retained_var\[^,\]*,\"\\w+R" } } */
+/* { dg-final { scan-assembler "\\.section\t\[^,\]*retained_fn\[^,\]*,\"\\w+R" } } */
+/* { dg-final { scan-assembler "\\.section\t\[^,\]*retain4\[^,\]*,\"\\w+R" } } */
+/* { dg-final { scan-assembler "\\.section\t\[^,\]*retain5\[^,\]*,\"\\w+R" } } */
+/* { dg-final { scan-assembler "\\.section\t\[^,\]*retain6\[^,\]*,\"\\w+R" } } */
+/* { dg-final { scan-assembler "\\.section\t\[^,\]*retain7\[^,\]*,\"\\w+R" } } */
+
+/* Test the retain attribute.  */
+#include "attr-retain-main.inc"
diff --git a/gcc/testsuite/c-c++-common/attr-retain-2.c b/gcc/testsuite/c-c++-common/attr-retain-2.c
new file mode 100644
index 00000000000..a69516547ae
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/attr-retain-2.c
@@ -0,0 +1,21 @@ 
+/* { dg-do compile } */
+/* { dg-require-effective-target retain } */
+/* { dg-options "-ffunction-sections -fdata-sections" } */
+/* { dg-final { scan-assembler "\\.section\t\[^,\]*retain0\[^,\]*,\"\\w+R" } } */
+/* { dg-final { scan-assembler "\\.section\t\[^,\]*retain1\[^,\]*,\"\\w+R" } } */
+/* { dg-final { scan-assembler "\\.section\t\[^,\]*retain2\[^,\]*,\"\\w+R" } } */
+/* { dg-final { scan-assembler "\\.section\t\[^,\]*retain3\[^,\]*,\"\\w+R" } } */
+/* { dg-final { scan-assembler "\\.section\t\[^,\]*sretain0\[^,\]*,\"\\w+R" } } */
+/* { dg-final { scan-assembler "\\.section\t\[^,\]*sretain1\[^,\]*,\"\\w+R" } } */
+/* { dg-final { scan-assembler "\\.section\t\[^,\]*sretain3\[^,\]*,\"\\w+R" } } */
+/* { dg-final { scan-assembler "\\.section\t\[^,\]*fretain0\[^,\]*,\"\\w+R" } } */
+/* { dg-final { scan-assembler "\\.section\t\[^,\]*retained_var\[^,\]*,\"\\w+R" } } */
+/* { dg-final { scan-assembler "\\.section\t\[^,\]*retained_fn\[^,\]*,\"\\w+R" } } */
+/* { dg-final { scan-assembler "\\.section\t\[^,\]*retain4\[^,\]*,\"\\w+R" } } */
+/* { dg-final { scan-assembler "\\.section\t\[^,\]*retain5\[^,\]*,\"\\w+R" } } */
+/* { dg-final { scan-assembler "\\.section\t\[^,\]*retain6\[^,\]*,\"\\w+R" } } */
+/* { dg-final { scan-assembler "\\.section\t\[^,\]*retain7\[^,\]*,\"\\w+R" } } */
+
+/* Test the retain attribute when -ffunction-sections and -fdata-sections
+   options are in use.  */
+#include "attr-retain-main.inc"
diff --git a/gcc/testsuite/c-c++-common/attr-retain-3.c b/gcc/testsuite/c-c++-common/attr-retain-3.c
new file mode 100644
index 00000000000..a9f2b20183c
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/attr-retain-3.c
@@ -0,0 +1,10 @@ 
+/* { dg-do compile } */
+/* { dg-require-effective-target retain } */
+
+typedef int int_retain __attribute__((retain)); /* { dg-warning "'retain' attribute ignored" } */
+
+void
+foo (void)
+{
+  int __attribute__((retain)) a; /* { dg-warning "'retain' attribute ignored" } */
+}
diff --git a/gcc/testsuite/c-c++-common/attr-retain-main.inc b/gcc/testsuite/c-c++-common/attr-retain-main.inc
new file mode 100644
index 00000000000..0ae3b71b9ce
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/attr-retain-main.inc
@@ -0,0 +1,26 @@ 
+/* The "retain" attribute set on this group of functions and data should protect
+   them from linker garbage collection.  */
+int __attribute__((retain)) retain0;
+int __attribute__((retain)) retain1 = 0;
+int __attribute__((retain)) retain2 = 1;
+const int __attribute__((retain)) retain3 = 2;
+static int __attribute__((retain)) sretain0;
+static int __attribute__((retain)) sretain1 = 0;
+static int __attribute__((retain)) sretain2 = 1;
+static const int __attribute__((retain)) sretain3 = 2;
+
+void __attribute__((retain)) fretain0 (void) {}
+
+int __attribute__((retain,section(".data.retained_var"))) var_retain_sec = 42;
+void __attribute__((retain,section(".text.retained_fn"))) fn_retain_sec (void) {}
+
+/* The section containing fdiscard2 should be garbage collected, but the static
+   variables defined inside it with the retain attribute applied should not.  */
+void
+fdiscard2 (void)
+{
+  static int __attribute__((retain)) retain4;
+  static int __attribute__((retain)) retain5 = 0;
+  static int __attribute__((retain)) retain6 = 1;
+  static const int __attribute__((retain)) retain7 = 2;
+}
diff --git a/gcc/testsuite/lib/target-supports.exp b/gcc/testsuite/lib/target-supports.exp
index 8439720baea..af38d7e1155 100644
--- a/gcc/testsuite/lib/target-supports.exp
+++ b/gcc/testsuite/lib/target-supports.exp
@@ -380,6 +380,15 @@  proc check_effective_target_noinit { } {
     return 0
 }
 
+# The retain attribute is only supported by some targets.
+# This proc returns 1 if it's supported, 0 if it's not.
+
+proc check_effective_target_retain { } {
+    return [check_no_compiler_messages retain_available assembly {
+	int __attribute__((retain)) a = 1;
+    }]
+}
+
 ###############################
 # proc check_visibility_available { what_kind }
 ###############################
diff --git a/gcc/tree-core.h b/gcc/tree-core.h
index 752bec31c3f..42e6e4b82f5 100644
--- a/gcc/tree-core.h
+++ b/gcc/tree-core.h
@@ -1691,6 +1691,7 @@  struct GTY(()) tree_decl_common {
   unsigned abstract_flag : 1;
   unsigned artificial_flag : 1;
   unsigned preserve_flag: 1;
+  unsigned retain_flag: 1;
   unsigned debug_expr_is_from : 1;
 
   unsigned lang_flag_0 : 1;
diff --git a/gcc/tree.h b/gcc/tree.h
index f43ac9f1942..731d6d8c558 100644
--- a/gcc/tree.h
+++ b/gcc/tree.h
@@ -2648,6 +2648,13 @@  extern tree vector_element_bits_tree (const_tree);
 #define DECL_PRESERVE_P(DECL) \
   DECL_COMMON_CHECK (DECL)->decl_common.preserve_flag
 
+/* Nonzero for a decl that is decorated using attribute retain.
+   This indicates to compiler tools that this decl needs to be preserved,
+   and to the link editor that the section containing the decl should not be
+   garbage collected.  */
+#define DECL_RETAIN_P(DECL) \
+  DECL_COMMON_CHECK (DECL)->decl_common.retain_flag
+
 /* For function local variables of COMPLEX and VECTOR types,
    indicates that the variable is not aliased, and that all
    modifications to the variable have been adjusted so that
diff --git a/gcc/varasm.c b/gcc/varasm.c
index ea0b59cf44a..dc7c7176a10 100644
--- a/gcc/varasm.c
+++ b/gcc/varasm.c
@@ -464,7 +464,8 @@  resolve_unique_section (tree decl, int reloc ATTRIBUTE_UNUSED,
   if (DECL_SECTION_NAME (decl) == NULL
       && targetm_common.have_named_sections
       && (flag_function_or_data_sections
-	  || DECL_COMDAT_GROUP (decl)))
+	  || DECL_COMDAT_GROUP (decl)
+	  || DECL_RETAIN_P (decl)))
     {
       targetm.asm_out.unique_section (decl, reloc);
       if (DECL_SECTION_NAME (decl))
@@ -6619,6 +6620,9 @@  default_section_type_flags (tree decl, const char *name, int reloc)
   if (decl && VAR_P (decl) && DECL_THREAD_LOCAL_P (decl))
     flags |= SECTION_TLS | SECTION_WRITE;
 
+  if (decl && DECL_RETAIN_P (decl))
+    flags |= SECTION_RETAIN;
+
   if (strcmp (name, ".bss") == 0
       || strncmp (name, ".bss.", 5) == 0
       || strncmp (name, ".gnu.linkonce.b.", 16) == 0
@@ -6738,6 +6742,8 @@  default_elf_asm_named_section (const char *name, unsigned int flags,
       if (flags & SECTION_MACH_DEP)
 	*f++ = MACH_DEP_SECTION_ASM_FLAG;
 #endif
+      if (flags & SECTION_RETAIN)
+	*f++ = 'R';
       *f = '\0';
     }