debug: Pass --gdwarf-N to assembler if fixed gas is detected during configure

> > As for the test assembly, I'd say we should take
> > #define F void foo (void) {}
> > F
> > compile it with
> > gcc -S -O2 -g1 -dA -gno-as-loc-support -fno-merge-debug-strings
> > remove .cfi_* directives, remove the ret instruction, change @function
> > and @progbits to %function and %progbits, change .uleb128 to just .byte,
> > I think all the values should be small enough, maybe change .value to
> > .2byte and .long to .4byte (whatever is most portable across different
> > arches and gas versions), simplify (shorten) strings and adjust
> > sizes, and do something with the .quad directives, that is dependent on
> > the address size, perhaps just take those attributes out and adjust
> > .debug_abbrev?  Finally, remove all comments (emit them in the first case
> > just to better understand the debug info).
>
> I'm afraid it is hard to avoid the .quad or .8byte.
> Here is a 64-bit address version that assembles fine by both x86_64 and
> aarch64 as.
> Unfortunately doesn't fail with broken gas versions with -gdwarf-2 without
> the nop, so we'll need at least a nop in there.
> Fortunately gcc/configure.ac already determines the right nop insn for the
> target, in $insn.
> So I guess what we want next is have the 32-bit version of this with .4byte
> instead of .8byte and just let's try to assemble both versions, first
> without -gdwarf-2 and the one that succeeds assemble again with -gdwarf-2
> and check for the duplicate .debug_line sections error.

Ok, here it is in patch form.
I've briefly tested it, with the older binutils I have around (no --gdwarf-N
support), with latest gas (--gdwarf-N that can be passed to as even when
compiling C/C++ etc. code and emitting .debug_line) and latest gas with Mark's fix
reverted (--gdwarf-N support, but can only pass it to as when assembling
user .s/.S files, not when compiling C/C++ etc.).

2020-10-07  Jakub Jelinek  <jakub@redhat.com>

	* configure.ac (HAVE_AS_GDWARF_5_DEBUG_FLAG,
	HAVE_AS_WORKING_DWARF_4_FLAG): New tests.
	* gcc.c (ASM_DEBUG_DWARF_OPTION): Define.
	(ASM_DEBUG_SPEC): Use ASM_DEBUG_DWARF_OPTION instead of
	"--gdwarf2".  Use %{cond:opt1;:opt2} style.
	(ASM_DEBUG_OPTION_DWARF_OPT): Define.
	(ASM_DEBUG_OPTION_SPEC): Define.
	(asm_debug_option): New variable.
	(asm_options): Add "%(asm_debug_option)".
	(static_specs): Add asm_debug_option entry.
	(static_spec_functions): Add dwarf-version-gt.
	(debug_level_greater_than_spec_func): New function.
	* config/darwin.h (ASM_DEBUG_OPTION_SPEC): Define.
	* config/darwin9.h (ASM_DEBUG_OPTION_SPEC): Redefine.
	* config.in: Regenerated.
	* configure: Regenerated.

1 files changed, 73 insertions, 4 deletions

diff --git a/gcc/gcc.c b/gcc/gcc.c
index 531f4e0..ff7b6c4 100644
--- a/gcc/gcc.c
+++ b/gcc/gcc.c
@@ -430,6 +430,7 @@ static const char *pass_through_libs_spec_func (int, const char **);
 static const char *dumps_spec_func (int, const char **);
 static const char *greater_than_spec_func (int, const char **);
 static const char *debug_level_greater_than_spec_func (int, const char **);
+static const char *dwarf_version_greater_than_spec_func (int, const char **);
 static const char *find_fortran_preinclude_file (int, const char **);
 static char *convert_white_space (char *);
 static char *quote_spec (char *);
@@ -876,22 +877,39 @@ proper position among the other output files.  */
 #endif /* HAVE_LD_COMPRESS_DEBUG >= 2 */
 
 /* Define ASM_DEBUG_SPEC to be a spec suitable for translating '-g'
-   to the assembler.  */
+   to the assembler, when compiling assembly sources only.  */
 #ifndef ASM_DEBUG_SPEC
+# if defined(HAVE_AS_GDWARF_5_DEBUG_FLAG) && defined(HAVE_AS_WORKING_DWARF_4_FLAG)
+/* If --gdwarf-N is supported and as can handle even compiler generated
+   .debug_line with it, supply --gdwarf-N in ASM_DEBUG_OPTION_SPEC rather
+   than in ASM_DEBUG_SPEC, so that it applies to both .s and .c etc.
+   compilations.  */
+#  define ASM_DEBUG_DWARF_OPTION ""
+# elif defined(HAVE_AS_GDWARF_5_DEBUG_FLAG)
+#  define ASM_DEBUG_DWARF_OPTION "%{%:dwarf-version-gt(4):--gdwarf-5;" \
+	"%:dwarf-version-gt(3):--gdwarf-4;"				\
+	"%:dwarf-version-gt(2):--gdwarf-3;"				\
+	":--gdwarf2}"
+# else
+#  define ASM_DEBUG_DWARF_OPTION "--gdwarf2"
+# endif
 # if defined(DBX_DEBUGGING_INFO) && defined(DWARF2_DEBUGGING_INFO) \
      && defined(HAVE_AS_GDWARF2_DEBUG_FLAG) && defined(HAVE_AS_GSTABS_DEBUG_FLAG)
 #  define ASM_DEBUG_SPEC						\
       (PREFERRED_DEBUGGING_TYPE == DBX_DEBUG				\
        ? "%{%:debug-level-gt(0):"					\
-	 "%{gdwarf*:--gdwarf2}%{!gdwarf*:%{g*:--gstabs}}}" ASM_MAP	\
+	 "%{gdwarf*:" ASM_DEBUG_DWARF_OPTION "};"			\
+	 ":%{g*:--gstabs}}" ASM_MAP					\
        : "%{%:debug-level-gt(0):"					\
-	 "%{gstabs*:--gstabs}%{!gstabs*:%{g*:--gdwarf2}}}" ASM_MAP)
+	 "%{gstabs*:--gstabs;"						\
+	 ":%{g*:" ASM_DEBUG_DWARF_OPTION "}}}" ASM_MAP)
 # else
 #  if defined(DBX_DEBUGGING_INFO) && defined(HAVE_AS_GSTABS_DEBUG_FLAG)
 #   define ASM_DEBUG_SPEC "%{g*:%{%:debug-level-gt(0):--gstabs}}" ASM_MAP
 #  endif
 #  if defined(DWARF2_DEBUGGING_INFO) && defined(HAVE_AS_GDWARF2_DEBUG_FLAG)
-#   define ASM_DEBUG_SPEC "%{g*:%{%:debug-level-gt(0):--gdwarf2}}" ASM_MAP
+#   define ASM_DEBUG_SPEC "%{g*:%{%:debug-level-gt(0):" \
+	ASM_DEBUG_DWARF_OPTION "}}" ASM_MAP
 #  endif
 # endif
 #endif
@@ -899,6 +917,32 @@ proper position among the other output files.  */
 # define ASM_DEBUG_SPEC ""
 #endif
 
+/* Define ASM_DEBUG_OPTION_SPEC to be a spec suitable for translating '-g'
+   to the assembler when compiling all sources.  */
+#ifndef ASM_DEBUG_OPTION_SPEC
+# if defined(HAVE_AS_GDWARF_5_DEBUG_FLAG) && defined(HAVE_AS_WORKING_DWARF_4_FLAG)
+#  define ASM_DEBUG_OPTION_DWARF_OPT					\
+	"%{%:dwarf-version-gt(4):--gdwarf-5 ;"				\
+	"%:dwarf-version-gt(3):--gdwarf-4 ;"				\
+	"%:dwarf-version-gt(2):--gdwarf-3 ;"				\
+	":--gdwarf2 }"
+#  if defined(DBX_DEBUGGING_INFO) && defined(DWARF2_DEBUGGING_INFO)
+#  define ASM_DEBUG_OPTION_SPEC						\
+      (PREFERRED_DEBUGGING_TYPE == DBX_DEBUG				\
+       ? "%{%:debug-level-gt(0):"					\
+	 "%{gdwarf*:" ASM_DEBUG_OPTION_DWARF_OPT "}}" 			\
+       : "%{%:debug-level-gt(0):"					\
+	 "%{!gstabs*:%{g*:" ASM_DEBUG_OPTION_DWARF_OPT "}}}")
+# elif defined(DWARF2_DEBUGGING_INFO)
+#   define ASM_DEBUG_OPTION_SPEC "%{g*:%{%:debug-level-gt(0):" \
+	ASM_DEBUG_OPTION_DWARF_OPT "}}"
+#  endif
+# endif
+#endif
+#ifndef ASM_DEBUG_OPTION_SPEC
+# define ASM_DEBUG_OPTION_SPEC ""
+#endif
+
 /* Here is the spec for running the linker, after compiling all files.  */
 
 /* This is overridable by the target in case they need to specify the
@@ -1113,6 +1157,7 @@ proper position among the other output files.  */
 #endif
 
 static const char *asm_debug = ASM_DEBUG_SPEC;
+static const char *asm_debug_option = ASM_DEBUG_OPTION_SPEC;
 static const char *cpp_spec = CPP_SPEC;
 static const char *cc1_spec = CC1_SPEC;
 static const char *cc1plus_spec = CC1PLUS_SPEC;
@@ -1212,6 +1257,7 @@ static const char *asm_options =
    to the assembler equivalents.  */
 "%{v} %{w:-W} %{I*} "
 #endif
+"%(asm_debug_option)"
 ASM_COMPRESS_DEBUG_SPEC
 "%a %Y %{c:%W{o*}%{!o*:-o %w%b%O}}%{!c:-o %d%w%u%O}";
 
@@ -1608,6 +1654,7 @@ static struct spec_list static_specs[] =
 {
   INIT_STATIC_SPEC ("asm",			&asm_spec),
   INIT_STATIC_SPEC ("asm_debug",		&asm_debug),
+  INIT_STATIC_SPEC ("asm_debug_option",		&asm_debug_option),
   INIT_STATIC_SPEC ("asm_final",		&asm_final_spec),
   INIT_STATIC_SPEC ("asm_options",		&asm_options),
   INIT_STATIC_SPEC ("invoke_as",		&invoke_as),
@@ -1690,6 +1737,7 @@ static const struct spec_function static_spec_functions[] =
   { "dumps",                    dumps_spec_func },
   { "gt",			greater_than_spec_func },
   { "debug-level-gt",		debug_level_greater_than_spec_func },
+  { "dwarf-version-gt",		dwarf_version_greater_than_spec_func },
   { "fortran-preinclude-file",	find_fortran_preinclude_file},
 #ifdef EXTRA_SPEC_FUNCTIONS
   EXTRA_SPEC_FUNCTIONS
@@ -10614,6 +10662,27 @@ debug_level_greater_than_spec_func (int argc, const char **argv)
   return NULL;
 }
 
+/* Returns "" if dwarf_version is greater than ARGV[ARGC-1].
+   Otherwise, return NULL.  */
+
+static const char *
+dwarf_version_greater_than_spec_func (int argc, const char **argv)
+{
+  char *converted;
+
+  if (argc != 1)
+    fatal_error (input_location,
+		 "wrong number of arguments to %%:dwarf-version-gt");
+
+  long arg = strtol (argv[0], &converted, 10);
+  gcc_assert (converted != argv[0]);
+
+  if (dwarf_version > arg)
+    return "";
+
+  return NULL;
+}
+
 static void
 path_prefix_reset (path_prefix *prefix)
 {