gnu: Add second ld-wrapper to work around readlink dereferencing bug.

Suggested by Mark H Weaver.

* gnu/packages/ld-wrapper2.in: New file.
* gnu-system.am (MISC_DISTRO_FILES): Add it.
* gnu/packages/commencement.scm (fixed-ld-wrapper): New procedure.

gnu-system.am

@@ -575,7 +575,8 @@ dist_patch_DATA =						\
   gnu/packages/patches/zathura-plugindir-environment-variable.patch
 
 MISC_DISTRO_FILES =				\
-  gnu/packages/ld-wrapper.in
+  gnu/packages/ld-wrapper.in			\
+  gnu/packages/ld-wrapper2.in
 
 bootstrapdir = $(guilemoduledir)/gnu/packages/bootstrap
 bootstrap_x86_64_linuxdir = $(bootstrapdir)/x86_64-linux

gnu/packages/commencement.scm

@@ -708,6 +708,19 @@ COREUTILS-FINAL vs. COREUTILS, etc."
 ;;; GCC toolchain.
 ;;;
 
+(define (fixed-ld-wrapper)
+  ;; FIXME: In this cycle, a bug was introduced in ld-wrapper: it would
+  ;; incorrectly flag ~/.guix-profile/lib/libfoo.so as "impure", due to a bug
+  ;; in its symlink resolution code.  To work around that while avoiding a
+  ;; full rebuild, use an ld-wrapper with the bug-fix for 'gcc-toolchain'.
+  (let ((orig (car (assoc-ref %final-inputs "ld-wrapper"))))
+    (package
+      (inherit orig)
+      (location (source-properties->location (current-source-location)))
+      (inputs `(("wrapper" ,(search-path %load-path
+                                         "gnu/packages/ld-wrapper2.in"))
+                ,@(package-inputs orig))))))
+
 (define (gcc-toolchain gcc)
   "Return a complete toolchain for GCC."
   (package
@@ -746,7 +759,7 @@ and binaries, plus debugging symbols in the 'debug' output), and Binutils.")
     ;; install everything that we need, and (2) to make sure ld-wrapper comes
     ;; before Binutils' ld in the user's profile.
     (inputs `(("gcc" ,gcc)
-              ("ld-wrapper" ,(car (assoc-ref %final-inputs "ld-wrapper")))
+              ("ld-wrapper" ,(fixed-ld-wrapper))
               ("binutils" ,binutils-final)
               ("libc" ,glibc-final)
               ("libc-debug" ,glibc-final "debug")))))

gnu/packages/ld-wrapper2.in

@@ -0,0 +1,201 @@
+#!@BASH@
+# -*- mode: scheme; coding: utf-8; -*-
+
+# XXX: We have to go through Bash because there's no command-line switch to
+# augment %load-compiled-path, and because of the silly 127-byte limit for
+# the shebang line in Linux.
+# Use `load-compiled' because `load' (and `-l') doesn't otherwise load our
+# .go file (see <http://bugs.gnu.org/12519>).
+
+main="(@ (gnu build-support ld-wrapper) ld-wrapper)"
+exec @GUILE@ -c "(load-compiled \"@SELF@.go\") (apply $main (cdr (command-line)))" "$@"
+!#
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2012, 2013, 2014, 2015 Ludovic Courtès <ludo@gnu.org>
+;;;
+;;; This file is part of GNU Guix.
+;;;
+;;; GNU Guix is free software; you can redistribute it and/or modify it
+;;; under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 3 of the License, or (at
+;;; your option) any later version.
+;;;
+;;; GNU Guix is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;;; GNU General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (gnu build-support ld-wrapper)
+  #:use-module (srfi srfi-1)
+  #:use-module (ice-9 match)
+  #:export (ld-wrapper))
+
+;;; Commentary:
+;;;
+;;; This is a wrapper for the linker.  Its purpose is to inspect the -L and
+;;; -l switches passed to the linker, add corresponding -rpath arguments, and
+;;; invoke the actual linker with this new set of arguments.
+;;;
+;;; The alternatives to this hack would be:
+;;;
+;;;   1. Using $LD_RUN_PATH.  However, that would tend to include more than
+;;;      needed in the RPATH; for instance, given a package with `libfoo' as
+;;;      an input, all its binaries would have libfoo in their RPATH,
+;;;      regardless of whether they actually NEED it.
+;;;
+;;;   2. Use a GCC "lib" spec string such as `%{L*:-rpath %*}', which adds a
+;;;      `-rpath LIBDIR' argument for each occurrence of `-L LIBDIR'.
+;;;      However, this doesn't work when $LIBRARY_PATH is used, because the
+;;;      additional `-L' switches are not matched by the above rule, because
+;;;      the rule only matches explicit user-provided switches.  See
+;;;      <http://gcc.gnu.org/ml/gcc-help/2012-09/msg00110.html> for details.
+;;;
+;;; As a bonus, this wrapper checks for "impurities"--i.e., references to
+;;; libraries outside the store.
+;;;
+;;; Code:
+
+(define %real-ld
+  ;; Name of the linker that we wrap.
+  "@LD@")
+
+(define %store-directory
+  ;; File name of the store.
+  (or (getenv "NIX_STORE") "/gnu/store"))
+
+(define %temporary-directory
+  ;; Temporary directory.
+  (or (getenv "TMPDIR") "/tmp"))
+
+(define %build-directory
+  ;; Top build directory when run from a builder.
+  (getenv "NIX_BUILD_TOP"))
+
+(define %allow-impurities?
+  ;; Whether to allow references to libraries outside the store.
+  (getenv "GUIX_LD_WRAPPER_ALLOW_IMPURITIES"))
+
+(define %debug?
+  ;; Whether to emit debugging output.
+  (getenv "GUIX_LD_WRAPPER_DEBUG"))
+
+(define %disable-rpath?
+  ;; Whether to disable automatic '-rpath' addition.
+  (getenv "GUIX_LD_WRAPPER_DISABLE_RPATH"))
+
+(define (readlink* file)
+  ;; Call 'readlink' until the result is not a symlink.
+  (define %max-symlink-depth 50)
+
+  (let loop ((file  file)
+             (depth 0))
+    (define (absolute target)
+      (if (absolute-file-name? target)
+          target
+          (string-append (dirname file) "/" target)))
+
+    (catch 'system-error
+      (lambda ()
+        (if (>= depth %max-symlink-depth)
+            file
+            (loop (absolute (readlink file)) (+ depth 1))))
+      (lambda args
+        (let ((errno (system-error-errno args)))
+          (if (or (= errno EINVAL) (= errno ENOENT))
+              file
+              (apply throw args)))))))
+
+(define (pure-file-name? file)
+  ;; Return #t when FILE is the name of a file either within the store
+  ;; (possibly via a symlink) or within the build directory.
+  (let ((file (readlink* file)))
+    (or (not (string-prefix? "/" file))
+        (string-prefix? %store-directory file)
+        (string-prefix? %temporary-directory file)
+        (and %build-directory
+             (string-prefix? %build-directory file)))))
+
+(define (store-file-name? file)
+  ;; Return #t when FILE is a store file, possibly indirectly.
+  (string-prefix? %store-directory (readlink* file)))
+
+(define (shared-library? file)
+  ;; Return #t when FILE denotes a shared library.
+  (or (string-suffix? ".so" file)
+      (let ((index (string-contains file ".so.")))
+        ;; Since we cannot use regexps during bootstrap, roll our own.
+        (and index
+             (string-every (char-set-union (char-set #\.) char-set:digit)
+                           (string-drop file (+ index 3)))))))
+
+(define (library-files-linked args)
+  ;; Return the file names of shared libraries explicitly linked against via
+  ;; `-l' or with an absolute file name in ARGS.
+  (define path+files
+    (fold (lambda (argument result)
+            (match result
+              ((library-path . library-files)
+               (cond ((string-prefix? "-L" argument) ;augment the search path
+                      (cons (append library-path
+                                    (list (string-drop argument 2)))
+                            library-files))
+                     ((string-prefix? "-l" argument) ;add library
+                      (let* ((lib  (string-append "lib"
+                                                  (string-drop argument 2)
+                                                  ".so"))
+                             (full (search-path library-path lib)))
+                        (if full
+                            (cons library-path
+                                  (cons full library-files))
+                            result)))
+                     ((and (string-prefix? %store-directory argument)
+                           (shared-library? argument)) ;add library
+                      (cons library-path
+                            (cons argument library-files)))
+                     (else
+                      result)))))
+          (cons '() '())
+          args))
+
+  (match path+files
+    ((path . files)
+     (reverse files))))
+
+(define (rpath-arguments library-files)
+  ;; Return the `-rpath' argument list for each of LIBRARY-FILES, a list of
+  ;; absolute file names.
+  (fold-right (lambda (file args)
+                ;; Add '-rpath' if and only if FILE is in the store; we don't
+                ;; want to add '-rpath' for files under %BUILD-DIRECTORY or
+                ;; %TEMPORARY-DIRECTORY because that could leak to installed
+                ;; files.
+                (cond ((and (not %disable-rpath?)
+                            (store-file-name? file))
+                       (cons* "-rpath" (dirname file) args))
+                      ((or %allow-impurities?
+                           (pure-file-name? file))
+                       args)
+                      (else
+                       (begin
+                         (format (current-error-port)
+                                 "ld-wrapper: error: attempt to use \
+impure library ~s~%"
+                                 file)
+                         (exit 1)))))
+              '()
+              library-files))
+
+(define (ld-wrapper . args)
+  ;; Invoke the real `ld' with ARGS, augmented with `-rpath' switches.
+  (let* ((libs (library-files-linked args))
+         (args (append args (rpath-arguments libs))))
+    (when %debug?
+      (format (current-error-port)
+              "ld-wrapper: invoking `~a' with ~s~%"
+              %real-ld args))
+    (apply execl %real-ld (basename %real-ld) args)))
+
+;;; ld-wrapper.scm ends here