Warn used and not used symbols in section with the same name

When SECTION_RETAIN is used, issue a warning when a symbol without used
attribute and a symbol with used attribute are placed in the section with
the same name, like

int __attribute__((used,section(".data.foo"))) foo2 = 2;
int __attribute__((section(".data.foo"))) foo1 = 1;

since assembler will put them in different sections with the same section
name.

gcc/

	PR target/98146
	* varasm.c (switch_to_section): Warn when a symbol without used
	attribute and a symbol with used attribute are placed in the
	section with the same name.

gcc/testsuite/

	PR target/98146
	* c-c++-common/attr-used-5.c: Updated.
	* c-c++-common/attr-used-6.c: Likewise.
	* c-c++-common/attr-used-7.c: Likewise.
	* c-c++-common/attr-used-8.c: Likewise.

1 files changed, 19 insertions, 3 deletions

diff --git a/gcc/varasm.c b/gcc/varasm.c
index cfec870..a1a8d3b 100644
--- a/gcc/varasm.c
+++ b/gcc/varasm.c
@@ -7765,11 +7765,27 @@ switch_to_section (section *new_section, tree decl)
 	{
 	  /* If the SECTION_RETAIN bit doesn't match, switch to a new
 	     section.  */
+	  tree used_decl, no_used_decl;
+
 	  if (DECL_PRESERVE_P (decl))
-	    new_section->common.flags |= SECTION_RETAIN;
+	    {
+	      new_section->common.flags |= SECTION_RETAIN;
+	      used_decl = decl;
+	      no_used_decl = new_section->named.decl;
+	    }
 	  else
-	    new_section->common.flags &= ~(SECTION_RETAIN
-					   | SECTION_DECLARED);
+	    {
+	      new_section->common.flags &= ~(SECTION_RETAIN
+					     | SECTION_DECLARED);
+	      used_decl = new_section->named.decl;
+	      no_used_decl = decl;
+	    }
+	  warning (OPT_Wattributes,
+		   "%+qD without %<used%> attribute and %qD with "
+		   "%<used%> attribute are placed in a section with "
+		   "the same name", no_used_decl, used_decl);
+	  inform (DECL_SOURCE_LOCATION (used_decl),
+		  "%qD was declared here", used_decl);
 	}
       else
 	return;