[Bug c++/105169] Compiling C++ code with -fpatchable-function-entry=16,14 results in references to discarded sections

["matz at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105169

Michael Matz <matz at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |matz at gcc dot gnu.org

--- Comment #8 from Michael Matz <matz at gcc dot gnu.org> ---
Something like this would be needed.  It's proof-of-concept.  It actually just
copy-pastes code from default_function_rodata_section without proper
integration
and caring for other cases handled there.  To be done properly it would need
abstracting what default_function_rodata_section does, just with a choosable
prefix.  Additionally the whole section dealing in GCC should be changed such
that internally not the section name is the only differentiator for the section
hash table: currently that's the reason the comdat name has to be appended
to the section name, although ELF doesn't need this for comdat sections.  So,
terrible hack, but ...

diff --git a/gcc/targhooks.c b/gcc/targhooks.c
index c9b5208853d..1ca5a4c3592 100644
--- a/gcc/targhooks.c
+++ b/gcc/targhooks.c
@@ -1963,14 +1963,36 @@ default_print_patchable_function_entry_1 (FILE *file,
       char buf[256];
       static int patch_area_number;
       section *previous_section = in_section;
+      section *sect;
       const char *asm_op = integer_asm_op (POINTER_SIZE_UNITS, false);

       gcc_assert (asm_op != NULL);
       patch_area_number++;
       ASM_GENERATE_INTERNAL_LABEL (buf, "LPFE", patch_area_number);

-      switch_to_section (get_section ("__patchable_function_entries",
-                                     flags, current_function_decl));
+      if (DECL_COMDAT_GROUP (current_function_decl) && HAVE_COMDAT_GROUP)
+       {
+         const char *dot;
+         size_t len;
+         char* rname;
+         const char *sname = "__patchable_function_entries";
+         const char *name = DECL_SECTION_NAME (current_function_decl);
+
+         dot = strchr (name + 1, '.');
+         if (!dot)
+           dot = name;
+         len = strlen (dot) + strlen (sname) + 1;
+         rname = (char *) alloca (len);
+
+         strcpy (rname, sname);
+         strcat (rname, dot);
+         sect = get_section (rname, (SECTION_LINKONCE | flags),
+                             current_function_decl);
+       }
+      else
+       sect = get_section ("__patchable_function_entries", flags,
+                           current_function_decl);
+      switch_to_section (sect);
       assemble_align (POINTER_SIZE);
       fputs (asm_op, file);
       assemble_name_raw (file, buf);