gdb/gdb-rhbz2192105-ftbs-dangling-pointer

From FEDORA_PATCHES Mon Sep 17 00:00:00 2001
From: Kevin Buettner <kevinb@redhat.com>
Date: Wed, 3 May 2023 11:28:24 -0700
Subject: gdb-rhbz2192105-ftbs-dangling-pointer
MIME-Version: 1.0
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;; Backport upstream patch fixing a "dangling pointer" build problem
;; first seen when building with GCC 13.1.1 20230426 (Red Hat ;; 13.1.1-1).

Pass const frame_info_ptr reference for skip_[language_]trampoline

g++ 13.1.1 produces a -Werror=dangling-pointer=

In file included from ../../binutils-gdb/gdb/frame.h:75,
                 from ../../binutils-gdb/gdb/symtab.h:40,
                 from ../../binutils-gdb/gdb/language.c:33:
In member function ‘void intrusive_list<T, AsNode>::push_empty(T&) [with T = frame_info_ptr; AsNode = intrusive_base_node<frame_info_ptr>]’,
    inlined from ‘void intrusive_list<T, AsNode>::push_back(reference) [with T = frame_info_ptr; AsNode = intrusive_base_node<frame_info_ptr>]’ at gdbsupport/intrusive_list.h:332:24,
    inlined from ‘frame_info_ptr::frame_info_ptr(const frame_info_ptr&)’ at gdb/frame.h:241:26,
    inlined from ‘CORE_ADDR skip_language_trampoline(frame_info_ptr, CORE_ADDR)’ at gdb/language.c:530:49:
gdbsupport/intrusive_list.h:415:12: error: storing the address of local variable ‘<anonymous>’ in ‘frame_info_ptr::frame_list.intrusive_list<frame_info_ptr>::m_back’ [-Werror=dangling-pointer=]
  415 |     m_back = &elem;
      |     ~~~~~~~^~~~~~~
gdb/language.c: In function ‘CORE_ADDR skip_language_trampoline(frame_info_ptr, CORE_ADDR)’:
gdb/language.c:530:49: note: ‘<anonymous>’ declared here
  530 |       CORE_ADDR real_pc = lang->skip_trampoline (frame, pc);
      |                           ~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~
gdb/frame.h:359:41: note: ‘frame_info_ptr::frame_list’ declared here
  359 |   static intrusive_list<frame_info_ptr> frame_list;
      |                                         ^~~~~~~~~~

Each new frame_info_ptr is being pushed on a static frame list and g++
cannot see why that is safe in case the frame_info_ptr is created and
destroyed immediately when passed as value.

It isn't clear why only in this one place g++ sees the issue (probably
because it can inline enough code in this specific case).

Since passing the frame_info_ptr as const reference is cheaper, use
that as workaround for this warning.

PR build/30413
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30413

Tested-by: Kevin Buettner <kevinb@redhat.com>
Reviewed-by: Kevin Buettner <kevinb@redhat.com>
Reviewed-by: Tom Tromey <tom@tromey.com>

diff --git a/gdb/c-lang.c b/gdb/c-lang.c
--- a/gdb/c-lang.c
+++ b/gdb/c-lang.c
@@ -1003,7 +1003,7 @@ class cplus_language : public language_defn
 
   /* See language.h.  */
 
-  CORE_ADDR skip_trampoline (frame_info_ptr fi,
+  CORE_ADDR skip_trampoline (const frame_info_ptr &fi,
 			     CORE_ADDR pc) const override
   {
     return cplus_skip_trampoline (fi, pc);
diff --git a/gdb/language.c b/gdb/language.c
--- a/gdb/language.c
+++ b/gdb/language.c
@@ -528,7 +528,7 @@ add_set_language_command ()
    Return the result from the first that returns non-zero, or 0 if all
    `fail'.  */
 CORE_ADDR 
-skip_language_trampoline (frame_info_ptr frame, CORE_ADDR pc)
+skip_language_trampoline (const frame_info_ptr &frame, CORE_ADDR pc)
 {
   for (const auto &lang : language_defn::languages)
     {
diff --git a/gdb/language.h b/gdb/language.h
--- a/gdb/language.h
+++ b/gdb/language.h
@@ -471,7 +471,7 @@ struct language_defn
      If that PC falls in a trampoline belonging to this language, return
      the address of the first pc in the real function, or 0 if it isn't a
      language tramp for this language.  */
-  virtual CORE_ADDR skip_trampoline (frame_info_ptr fi, CORE_ADDR pc) const
+  virtual CORE_ADDR skip_trampoline (const frame_info_ptr &fi, CORE_ADDR pc) const
   {
     return (CORE_ADDR) 0;
   }
@@ -789,7 +789,7 @@ extern const char *language_str (enum language);
 
 /* Check for a language-specific trampoline.  */
 
-extern CORE_ADDR skip_language_trampoline (frame_info_ptr, CORE_ADDR pc);
+extern CORE_ADDR skip_language_trampoline (const frame_info_ptr &, CORE_ADDR pc);
 
 /* Return demangled language symbol, or NULL.  */
 extern gdb::unique_xmalloc_ptr<char> language_demangle
diff --git a/gdb/objc-lang.c b/gdb/objc-lang.c
--- a/gdb/objc-lang.c
+++ b/gdb/objc-lang.c
@@ -282,7 +282,7 @@ class objc_language : public language_defn
 
   /* See language.h.  */
 
-  CORE_ADDR skip_trampoline (frame_info_ptr frame,
+  CORE_ADDR skip_trampoline (const frame_info_ptr &frame,
 			     CORE_ADDR stop_pc) const override
   {
     struct gdbarch *gdbarch = get_frame_arch (frame);