[PATCH] PE/COFF: Implement visibility attribute via .drectve

On PE/COFF targets (MinGW, Cygwin), the visibility attribute was
previously ignored with a warning.  This patch makes it functional
by emitting -exclude-symbols directives into the .drectve section,
matching Clang's behavior.  The GNU linker already reads and
respects these directives during auto-export, so hidden/internal
symbols are now correctly excluded from DLL exports.

gcc/ChangeLog:

	* config/mingw/winnt.cc (i386_pe_assemble_visibility): Emit
	-exclude-symbols directive into .drectve for VISIBILITY_HIDDEN
	and VISIBILITY_INTERNAL instead of warning.

gcc/testsuite/ChangeLog:

	* gcc.target/i386/visibility-hidden-mingw.c: New test.

Signed-off-by: Oleg Tolmatcev <[email protected]>
---
 gcc/config/mingw/winnt.cc                     | 20 +++++++++-------
 .../gcc.target/i386/visibility-hidden-mingw.c | 24 +++++++++++++++++++
 2 files changed, 36 insertions(+), 8 deletions(-)
 create mode 100644 gcc/testsuite/gcc.target/i386/visibility-hidden-mingw.c

diff --git a/gcc/config/mingw/winnt.cc b/gcc/config/mingw/winnt.cc
index 66d7450652..6f2d85b090 100644
--- a/gcc/config/mingw/winnt.cc
+++ b/gcc/config/mingw/winnt.cc
@@ -256,18 +256,22 @@ i386_pe_maybe_mangle_decl_assembler_name (tree decl, tree id)
 
 /* Emit an assembler directive to set symbol for DECL visibility to
    the visibility type VIS, which must not be VISIBILITY_DEFAULT.
-   As for PE there is no hidden support in gas, we just warn for
-   user-specified visibility attributes.  */
+   Emit a -exclude-symbols directive into .drectve, compatible with
+   what Clang emits for hidden visibility on PE/COFF.  */
 
 void
-i386_pe_assemble_visibility (tree decl, int)
+i386_pe_assemble_visibility (tree decl, int vis)
 {
-  if (!decl
-      || !lookup_attribute ("visibility", DECL_ATTRIBUTES (decl)))
+  if (!decl)
     return;
-  if (!DECL_ARTIFICIAL (decl))
-    warning (OPT_Wattributes, "visibility attribute not supported "
-			      "in this configuration; ignored");
+
+  if (vis == VISIBILITY_HIDDEN || vis == VISIBILITY_INTERNAL)
+    {
+      tree id = DECL_ASSEMBLER_NAME (decl);
+      const char *name = IDENTIFIER_POINTER (id);
+      drectve_section ();
+      fprintf (asm_out_file, "\t.ascii \" -exclude-symbols:%s\"\n", name);
+    }
 }
 
 #if !defined (TARGET_AARCH64_MS_ABI)
diff --git a/gcc/testsuite/gcc.target/i386/visibility-hidden-mingw.c b/gcc/testsuite/gcc.target/i386/visibility-hidden-mingw.c
new file mode 100644
index 0000000000..12d792631d
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/visibility-hidden-mingw.c
@@ -0,0 +1,24 @@
+/* { dg-do link { target *-*-mingw* *-*-cygwin* } } */
+/* { dg-require-dll "" } */
+/* { dg-options "-shared -fvisibility=hidden -Wl,--output-def,visibility-hidden-mingw.def" } */
+
+void __attribute__((visibility("default"))) exported_func(void) {}
+void hidden_func(void) {}
+void __attribute__((visibility("hidden"))) explicit_hidden_func(void) {}
+void __attribute__((visibility("internal"))) internal_func(void) {}
+
+/* exported_func has default visibility, so it should be exported.  */
+/* { dg-final { scan-file visibility-hidden-mingw.def "(?n)^\\s*exported_func(?:\\s+@\[0-9\]+)?$" } } */
+
+/* hidden_func gets hidden from -fvisibility=hidden, so it should not be
+   auto-exported.  */
+/* { dg-final { scan-file-not visibility-hidden-mingw.def "(?n)^\\s*hidden_func(?:\\s+@\[0-9\]+)?$" } } */
+
+/* explicit_hidden_func is explicitly hidden, so it should not be
+   auto-exported.  */
+/* { dg-final { scan-file-not visibility-hidden-mingw.def "(?n)^\\s*explicit_hidden_func(?:\\s+@\[0-9\]+)?$" } } */
+
+/* internal_func has internal visibility, so it should not be auto-exported.  */
+/* { dg-final { scan-file-not visibility-hidden-mingw.def "(?n)^\\s*internal_func(?:\\s+@\[0-9\]+)?$" } } */
+
+/* { dg-final { remove-build-file "visibility-hidden-mingw.def" } } */
-- 
2.55.0.windows.1