[Bug tdep/30028] [gdb/tdep, x86_64] Epilogue unwinder preferred over dwarf unwinder based on gcc 4.4

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

https://sourceware.org/bugzilla/show_bug.cgi?id=30028

--- Comment #7 from Tom de Vries <vries at gcc dot gnu.org> ---
(In reply to Tom de Vries from comment #6)
> (In reply to Tom de Vries from comment #5)
> > So, maybe we should just flip the switch on the default assumption.
> 
> Like so:
> ...
> diff --git a/gdb/amd64-tdep.c b/gdb/amd64-tdep.c
> index 76e843ecc35..86e12b4304a 100644
> --- a/gdb/amd64-tdep.c
> +++ b/gdb/amd64-tdep.c
> @@ -2905,7 +2905,7 @@ amd64_stack_frame_destroyed_p
>    struct compunit_symtab *cust;
>  
>    cust = find_pc_compunit_symtab (pc);
> -  if (cust != NULL && cust->epilogue_unwind_valid ())
> +  if (cust == NULL || cust->epilogue_unwind_valid ())
>      return 0;
>  
>    if (target_read_memory (pc, &insn, 1))
> diff --git a/gdb/i386-tdep.c b/gdb/i386-tdep.c
> index 580664d2ce5..46ad2913788 100644
> --- a/gdb/i386-tdep.c
> +++ b/gdb/i386-tdep.c
> @@ -2222,7 +2222,7 @@ i386_stack_frame_destroyed_p
>    struct compunit_symtab *cust;
>  
>    cust = find_pc_compunit_symtab (pc);
> -  if (cust != NULL && cust->epilogue_unwind_valid ())
> +  if (cust == NULL || cust->epilogue_unwind_valid ())
>      return 0;
>  
>    if (target_read_memory (pc, &insn, 1))
> ...

And likewise:
...
diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
index 44b54f77de9..44e85ebcfe9 100644
--- a/gdb/dwarf2/read.c
+++ b/gdb/dwarf2/read.c
@@ -8484,7 +8484,15 @@ process_full_comp_unit (dwarf2_cu *cu, enum language
pretend_la
nguage)
       if (cu->has_loclist && gcc_4_minor >= 5)
        cust->set_locations_valid (true);

-      if (gcc_4_minor >= 5)
+      if (cu->producer == nullptr)
+       /* In absence of producer information, optimistically assume that we're
+          not dealing with gcc < 4.5.0.  */
+       cust->set_epilogue_unwind_valid (true);
+      if (!producer_is_gcc (cu->producer, nullptr, nullptr))
+       /* Not gcc.  */
+       cust->set_epilogue_unwind_valid (true);
+      else if (gcc_4_minor >= 5)
+       /* gcc >= 4.5.0.  */
        cust->set_epilogue_unwind_valid (true);

       cust->set_call_site_htab (cu->call_site_htab);
...

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