[gcc r14-4108] Darwin, debug : Switch to DWARF 3 or 4 when dsymutil supports it.

[gcc r14-4108] Darwin, debug : Switch to DWARF 3 or 4 when dsymutil supports it.

[Iain D Sandoe]

https://gcc.gnu.org/g:47346acb72b50d178dae72393c851d57beec383f

commit r14-4108-g47346acb72b50d178dae72393c851d57beec383f
Author: Iain Sandoe <iain@sandoe.co.uk>
Date:   Sun Sep 17 15:56:07 2023 +0100

    Darwin,debug : Switch to DWARF 3 or 4 when dsymutil supports it.
    
    The main reason that Darwin has been using DWARF2 only as debug is that
    earlier debug linkers (dsymutil) did not support any extensions to this
    so that the default "non-strict" mode used in GCC would cause tool errors.
    
    There are two sources for dsymutil, those based off a closed source base
    "dwarfutils" and those based off LLVM.
    
    For dsymutil versions based off LLVM-7+ we can use up to DWARF-4, and for
    versions based on dwarfutils 121+ we can use DWARF-3.
    
    Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
    
    gcc/ChangeLog:
    
            * config/darwin-protos.h (enum darwin_external_toolchain): New.
            * config/darwin.cc (DSYMUTIL_VERSION): New.
            (darwin_override_options): Choose the default debug DWARF version
            depending on the configured dsymutil version.

Diff:
---
 gcc/config/darwin-protos.h | 11 +++++++++++
 gcc/config/darwin.cc       | 33 +++++++++++++++++++++++++++++----
 2 files changed, 40 insertions(+), 4 deletions(-)

diff --git a/gcc/config/darwin-protos.h b/gcc/config/darwin-protos.h
index 747745fa577..9df358ee7d3 100644
--- a/gcc/config/darwin-protos.h
+++ b/gcc/config/darwin-protos.h
@@ -129,4 +129,15 @@ extern void darwin_patch_builtins (void);
 extern void darwin_rename_builtins (void);
 extern bool darwin_libc_has_function (enum function_class fn_class, tree);
 
+/* For this port, there are several possible sources for external toolchain
+   components (e.g. as, ld, dsymutil) and we have to alter the allowable
+   output in response to which version and source is in use.  */
+enum darwin_external_toolchain {
+  DET_UNKNOWN=0,
+  CCTOOLS,
+  DWARFUTILS,
+  LLVM,
+  CLANG
+};
+
 #endif /* CONFIG_DARWIN_PROTOS_H */
diff --git a/gcc/config/darwin.cc b/gcc/config/darwin.cc
index 154a2b2755a..d8c8607892b 100644
--- a/gcc/config/darwin.cc
+++ b/gcc/config/darwin.cc
@@ -114,6 +114,19 @@ static bool ld_needs_eh_markers = false;
 /* Emit a section-start symbol for mod init and term sections.  */
 static bool ld_init_term_start_labels = false;
 
+/* The source and version of dsymutil in use.  */
+#ifndef DSYMUTIL_VERSION
+# warning Darwin toolchain without a defined dsymutil.
+# define DSYMUTIL_VERSION DET_UNKNOWN,0,0,0
+#endif
+
+struct {
+  darwin_external_toolchain kind; /* cctools, llvm, clang etc.  */
+  int major; /* version number.  */
+  int minor;
+  int tiny;
+} dsymutil_version = {DSYMUTIL_VERSION};
+
 /* Section names.  */
 section * darwin_sections[NUM_DARWIN_SECTIONS];
 
@@ -3357,14 +3370,26 @@ darwin_override_options (void)
 		  global_options.x_flag_objc_abi);
     }
 
-  /* Don't emit DWARF3/4 unless specifically selected.  This is a
-     workaround for tool bugs.  */
+  /* Limit DWARF to the chosen version, the linker and debug linker might not
+     be able to consume newer structures.  */
   if (!OPTION_SET_P (dwarf_strict))
     dwarf_strict = 1;
+
   if (!OPTION_SET_P (dwarf_version))
-    dwarf_version = 2;
+    {
+      /* External toolchains based on LLVM or clang 7+ have support for
+	 dwarf-4.  */
+      if ((dsymutil_version.kind == LLVM && dsymutil_version.major >= 7)
+	  || (dsymutil_version.kind == CLANG && dsymutil_version.major >= 7))
+	dwarf_version = 4;
+      else if (dsymutil_version.kind == DWARFUTILS
+	       && dsymutil_version.major >= 121)
+	dwarf_version = 3;  /* From XC 6.4.  */
+      else
+	dwarf_version = 2;  /* Older cannot safely exceed dwarf-2.  */
+    }
 
-  if (OPTION_SET_P (dwarf_split_debug_info))
+  if (OPTION_SET_P (dwarf_split_debug_info) && dwarf_split_debug_info)
     {
       inform (input_location,
 	      "%<-gsplit-dwarf%> is not supported on this platform, ignored");