[PATCH][v2] Always default to DWARF2_DEBUG if not specified, warn about deprecated STABS

[Richard Biener <rguenther@suse.de>]

This makes defaults.h choose DWARF2_DEBUG if PREFERRED_DEBUGGING_TYPE
is not specified by the target and NO_DEBUG if DWARF is not supported.

It also makes us warn when STABS is enabled and removes the corresponding
diagnostic from the Ada frontend.  The warnings are pruned from the
testsuite output via prune_gcc_output.

This leaves the following targets without debug support:

 pdp11-*-*   pdp11 is a.out, dwarf support is difficult
 m68k*-*-openbsd*  it looks like this is a.out as well, at least it does
                   not pretend to support DWARF
 hppa[12]*-*-hpux10*  does seem to not support DWARF
 vax-*-openbsd*  seems to be a.out as well, does not support DWARF

behavior will be like

> ./cc1 -quiet t.c -g
cc1: warning: target system does not support debug output
> ./cc1 -quiet t.c -gstabs
t.c: warning: STABS debugging information is obsolete and not supported anymore

that is, -g is unsupported but -gstabs will generate STABS (the above
is for pdp11).  It would be nice if maintainers could confirm the above
listed configurations do not support DWARF and weight in whether to
(apart from pdp11) the specific configurations can be obsoleted or
adjusted.  It looks like we do not have any openbsd maintainer.
I've discussed the situation for pdp11 with Paul already at some point
but we didn't reach any conclusion besides that it would be nice to
move pdp11 to ELF.


2021-09-10  Richard Biener  <rguenther@suse.de>

gcc/
	* defaults.h (PREFERRED_DEBUGGING_TYPE): Choose DWARF2_DEBUG
	or NO_DEBUG.
	* toplev.c (process_options): Warn when STABS debugging is
	enabled.

gcc/ada/
	* gcc-interface/misc.c (gnat_post_options): Do not warn
	about DBX_DEBUG use here.

gcc/testsuite/
	* lib/prune.exp: Prune STABS obsoletion message.
---
 gcc/ada/gcc-interface/misc.c |  6 ------
 gcc/defaults.h               | 27 ++++-----------------------
 gcc/testsuite/lib/prune.exp  |  3 +++
 gcc/toplev.c                 |  5 +++++
 4 files changed, 12 insertions(+), 29 deletions(-)

diff --git a/gcc/ada/gcc-interface/misc.c b/gcc/ada/gcc-interface/misc.c
index 96199bd4b63..87a4c8662cb 100644
--- a/gcc/ada/gcc-interface/misc.c
+++ b/gcc/ada/gcc-interface/misc.c
@@ -274,12 +274,6 @@ gnat_post_options (const char **pfilename ATTRIBUTE_UNUSED)
   if (!global_options_set.x_flag_diagnostics_show_caret)
     global_dc->show_caret = false;
 
-  /* Warn only if STABS is not the default: we don't want to emit a warning if
-     the user did not use a -gstabs option.  */
-  if (PREFERRED_DEBUGGING_TYPE != DBX_DEBUG && write_symbols == DBX_DEBUG)
-    warning (0, "STABS debugging information for Ada is obsolete and not "
-		"supported anymore");
-
   /* Copy global settings to local versions.  */
   gnat_encodings = global_options.x_gnat_encodings;
   optimize = global_options.x_optimize;
diff --git a/gcc/defaults.h b/gcc/defaults.h
index ba79a8e48ed..773b93b1a2e 100644
--- a/gcc/defaults.h
+++ b/gcc/defaults.h
@@ -900,34 +900,15 @@ see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
 #define DEFAULT_GDB_EXTENSIONS 1
 #endif
 
-/* If more than one debugging type is supported, you must define
-   PREFERRED_DEBUGGING_TYPE to choose the default.  */
-
-#if 1 < (defined (DBX_DEBUGGING_INFO) \
-         + defined (DWARF2_DEBUGGING_INFO) + defined (XCOFF_DEBUGGING_INFO) \
-         + defined (VMS_DEBUGGING_INFO))
 #ifndef PREFERRED_DEBUGGING_TYPE
-#error You must define PREFERRED_DEBUGGING_TYPE
-#endif /* no PREFERRED_DEBUGGING_TYPE */
-
-/* If only one debugging format is supported, define PREFERRED_DEBUGGING_TYPE
-   here so other code needn't care.  */
-#elif defined DBX_DEBUGGING_INFO
-#define PREFERRED_DEBUGGING_TYPE DBX_DEBUG
-
-#elif defined DWARF2_DEBUGGING_INFO || defined DWARF2_LINENO_DEBUGGING_INFO
+/* We default to DWARF2_DEBUGGING_INFO.  */
+#if defined DWARF2_DEBUGGING_INFO || defined DWARF2_LINENO_DEBUGGING_INFO
 #define PREFERRED_DEBUGGING_TYPE DWARF2_DEBUG
-
-#elif defined VMS_DEBUGGING_INFO
-#define PREFERRED_DEBUGGING_TYPE VMS_AND_DWARF2_DEBUG
-
-#elif defined XCOFF_DEBUGGING_INFO
-#define PREFERRED_DEBUGGING_TYPE XCOFF_DEBUG
-
 #else
-/* No debugging format is supported by this target.  */
+/* DWARF is not supported by this target.  */
 #define PREFERRED_DEBUGGING_TYPE NO_DEBUG
 #endif
+#endif
 
 #ifndef FLOAT_LIB_COMPARE_RETURNS_BOOL
 #define FLOAT_LIB_COMPARE_RETURNS_BOOL(MODE, COMPARISON) false
diff --git a/gcc/testsuite/lib/prune.exp b/gcc/testsuite/lib/prune.exp
index 91f165bec38..c390524babb 100644
--- a/gcc/testsuite/lib/prune.exp
+++ b/gcc/testsuite/lib/prune.exp
@@ -90,6 +90,9 @@ proc prune_gcc_output { text } {
     # Ignore dsymutil warning (tool bug is actually linker)
     regsub -all "(^|\n)\[^\n\]*could not find object file symbol for symbol\[^\n\]*" $text "" text
 
+    # Ignore stabs obsoletion warnings
+    regsub -all "(^|\n)\[^\n\]*\[Ww\]arning: STABS debugging information is obsolete and not supported anymore\[^\n\]*" $text "" text
+
     # If dg-enable-nn-line-numbers was provided, then obscure source-margin
     # line numbers by converting them to "NN" form.
     set text [maybe-handle-nn-line-numbers $text]
diff --git a/gcc/toplev.c b/gcc/toplev.c
index 14d1335e79e..2b58fd373bf 100644
--- a/gcc/toplev.c
+++ b/gcc/toplev.c
@@ -1452,6 +1452,11 @@ process_options (void)
       && ctf_debug_info_level == CTFINFO_LEVEL_NONE)
     write_symbols = NO_DEBUG;
 
+  /* Warn if STABS debug gets enabled.  */
+  if (write_symbols & DBX_DEBUG)
+    warning (0, "STABS debugging information is obsolete and not "
+	     "supported anymore");
+
   if (write_symbols == NO_DEBUG)
     ;
 #if defined(DBX_DEBUGGING_INFO)
-- 
2.31.1