Make using separate debugging info easier.

pkgs/applications/version-management/git-and-tools/git/default.nix

@@ -153,6 +153,7 @@ stdenv.mkDerivation {
      '');
 
   enableParallelBuilding = true;
+  separateDebugInfo = true;
 
   meta = {
     homepage = http://git-scm.com/;

pkgs/build-support/setup-hooks/separate-debug-info.sh

@@ -1,19 +1,19 @@
 export NIX_SET_BUILD_ID=1
-export NIX_LDFLAGS+=" --compress-debug-sections=zlib"
-export NIX_CFLAGS_COMPILE+=" -ggdb -Wa,--compress-debug-sections"
+export NIX_CFLAGS_COMPILE+=' -ggdb'
 dontStrip=1
 
 fixupOutputHooks+=(_separateDebugInfo)
 
 _separateDebugInfo() {
-    local dst="${debug:-$out}"
-    if [ "$prefix" = "$dst" ]; then return; fi
+    local debugout="${debug:-$out}"
+    if [ "$prefix" = "$debugout" ]; then return; fi
 
-    dst="$dst/lib/debug/.build-id"
+    local hashandname="$(basename "$debugout")"
+    local debugpath="$(dirname "$debugout")/${hashandname:0:2} ${hashandname:2}"
 
     # Find executables and dynamic libraries.
     local i magic
-    while IFS= read -r -d $'\0' i; do
+    while read -r -d $'\0' i; do
         if ! isELF "$i"; then continue; fi
 
         # Extract the Build ID. FIXME: there's probably a cleaner way.
@@ -25,11 +25,18 @@ _separateDebugInfo() {
 
         # Extract the debug info.
         header "separating debug info from $i (build ID $id)"
-        mkdir -p "$dst/${id:0:2}"
-        objcopy --only-keep-debug "$i" "$dst/${id:0:2}/${id:2}.debug"
-        strip --strip-debug "$i"
-
+        local relpath="lib/debug/.build-id/${id:0:2}/${id:2}.debug"
+        local debugfile="$debugout/$relpath"
+        mkdir -p $(dirname "$debugfile")
+        objcopy --only-keep-debug --compress-debug-sections "$i" "$debugfile"
         # Also a create a symlink <original-name>.debug.
-        ln -sfn ".build-id/${id:0:2}/${id:2}.debug" "$dst/../$(basename "$i")"
+        ln -sfn ".build-id/${id:0:2}/${id:2}.debug" "$debugout/lib/debug/$(basename "$i").debug"
+
+        if ! objdump -sj .nix_debug "$i" &> /dev/null; then
+            # The space is to prevent a reference.
+            objcopy --add-section=.nix_debug=<(echo "$debugpath/$relpath") "$i"
+        fi
+        strip $commonStripFlags "$i"
+
     done < <(find "$prefix" -type f -print0)
 }

pkgs/development/libraries/glibc/common.nix

@@ -26,6 +26,7 @@ stdenv.mkDerivation ({
   inherit (stdenv) is64bit;
 
   enableParallelBuilding = true;
+  separateDebugInfo = true;
 
   patches =
     [ /* Have rpcgen(1) look for cpp(1) in $PATH.  */

pkgs/development/tools/misc/gdb/default.nix

@@ -1,5 +1,5 @@
 { fetchurl, stdenv, ncurses, readline, gmp, mpfr, expat, texinfo, zlib
-, dejagnu, perl, pkgconfig
+, dejagnu, perl, pkgconfig, binutils, nix
 , python ? null
 , guile ? null
 , target ? null
@@ -21,6 +21,8 @@ let
       stdenv.system == "i686-gnu"
       || (stdenv ? cross && stdenv.cross.config == "i586-pc-gnu");
 
+  nixExtension = ./nix.py;
+
 in
 
 assert isGNU -> mig != null && hurd != null;
@@ -42,6 +44,7 @@ stdenv.mkDerivation rec {
     ++ stdenv.lib.optional doCheck dejagnu;
 
   enableParallelBuilding = true;
+  separateDebugInfo = true;
 
   configureFlags = with stdenv.lib;
     [ "--with-gmp=${gmp}" "--with-mpfr=${mpfr}" "--with-system-readline"
@@ -64,6 +67,9 @@ stdenv.mkDerivation rec {
 
   postInstall =
     '' # Remove Info files already provided by Binutils and other packages.
+       sed '-es|"objcopy"|"${binutils}/bin/objcopy"|' \
+           '-es|"nix-store"|"${nix.out}/bin/nix-store"|' \
+           '${nixExtension}' > "$out/share/gdb/python/gdb/command/nix.py"
        rm -v $out/share/info/bfd.info
     '';
 

pkgs/development/tools/misc/gdb/nix.py

@@ -0,0 +1,67 @@
+import os
+import subprocess
+
+import gdb
+
+_objects_without_symbols_loaded = set()
+
+def _new_objfile(event):
+	_load(event.new_objfile)
+
+gdb.events.new_objfile.connect(_new_objfile)
+
+def _clear_objfiles(event):
+	_objects_without_symbols_loaded.clear()
+
+gdb.events.clear_objfiles.connect(_clear_objfiles)
+
+def _get_debug_file_path(obj):
+	try:
+		out = subprocess.check_output([
+			"objcopy",
+			"--dump-section=.nix_debug=/dev/stdout",
+			obj.filename,
+			"/dev/null",
+		], stderr=subprocess.STDOUT)
+		if b"File in wrong format" in out:
+			# objdump isn't exiting with failure in this case.
+			return None
+		return str(out).replace(" ", "", 1).rstrip()
+	except:
+		return None
+
+def _load(obj):
+	debugfile = _get_debug_file_path(obj)
+	if not debugfile:
+		return
+
+	try:
+		obj.add_separate_debug_file(debugfile)
+		gdb.write("Loaded symbols for {}.\n".format(obj.username))
+		_objects_without_symbols_loaded.discard(obj)
+	except Exception as e:
+		_objects_without_symbols_loaded.add(obj)
+		gdb.write("Error loading debug symbols: {}\n".format(e))
+		gdb.write("From: {}\n".format(debugfile, e))
+		gdb.write("For:  {}\n".format(obj.username))
+		if not os.path.exists(debugfile):
+			gdb.write("The debug file doesn't exists.\n")
+			gdb.write("You can download missing debug files with 'nix-download-debug'.\n")
+
+def _download(objs):
+	debugfiles = [_get_debug_file_path(obj) for obj in objs]
+	subprocess.check_call(["nix-store", "-rk"] + debugfiles)
+
+class CommandNixDownloadDebug(gdb.Command):
+	def __init__(self):
+		super(CommandNixDownloadDebug, self).__init__("nix-download-debug", gdb.COMMAND_USER)
+
+	def invoke(self, arg, from_tty):
+		assert not arg
+		try:
+			_download(_objects_without_symbols_loaded)
+		finally:
+			for obj in list(_objects_without_symbols_loaded):
+				_load(obj)
+
+CommandNixDownloadDebug()

pkgs/tools/compression/xz/default.nix

@@ -10,6 +10,8 @@ stdenv.mkDerivation rec {
 
   outputs = [ "dev" "out" "bin" "man" "doc" ];
 
+  enableParallelBuilding = true;
+  separateDebugInfo = true;
   doCheck = true;
 
   # In stdenv-linux, prevent a dependency on bootstrap-tools.