gremlin: Add 'strip-runpath'.

* guix/build/gremlin.scm (strip-runpath): New procedure.
* tests/gremlin.scm (c-compiler): New variable.
("strip-runpath"): New test.

guix/build/gremlin.scm

@@ -41,7 +41,8 @@
             elf-dynamic-info-runpath
             expand-origin
 
-            validate-needed-in-runpath))
+            validate-needed-in-runpath
+            strip-runpath))
 
 ;;; Commentary:
 ;;;
@@ -320,4 +321,47 @@ be found in RUNPATH ~s~%"
           ;;   (format (current-error-port) "~a is OK~%" file))
           (null? not-found))))))
 
+(define (strip-runpath file)
+  "Remove from the DT_RUNPATH of FILE any entries that are not necessary
+according to DT_NEEDED."
+  (define (minimal-runpath needed runpath)
+    (filter (lambda (directory)
+              (and (string-prefix? "/" directory)
+                   (any (lambda (lib)
+                          (file-exists? (string-append directory "/" lib)))
+                        needed)))
+            runpath))
+
+  (define port
+    (open-file file "r+b"))
+
+  (catch #t
+    (lambda ()
+      (let* ((elf      (parse-elf (get-bytevector-all port)))
+             (entries  (dynamic-entries elf (dynamic-link-segment elf)))
+             (needed   (filter-map (lambda (entry)
+                                     (and (= (dynamic-entry-type entry)
+                                             DT_NEEDED)
+                                          (dynamic-entry-value entry)))
+                                   entries))
+             (runpath  (find (lambda (entry)
+                               (= DT_RUNPATH (dynamic-entry-type entry)))
+                             entries))
+             (old      (search-path->list
+                        (dynamic-entry-value runpath)))
+             (new      (minimal-runpath needed old)))
+        (unless (equal? old new)
+          (format (current-error-port)
+                  "~a: stripping RUNPATH to ~s (removed ~s)~%"
+                  file new
+                  (lset-difference string=? old new))
+          (seek port (dynamic-entry-offset runpath) SEEK_SET)
+          (put-bytevector port (string->utf8 (string-join new ":")))
+          (put-u8 port 0))
+        (close-port port)
+        new))
+    (lambda (key . args)
+      (false-if-exception (close-port port))
+      (apply throw key args))))
+
 ;;; gremlin.scm ends here

tests/gremlin.scm

@@ -1,5 +1,5 @@
 ;;; GNU Guix --- Functional package management for GNU
-;;; Copyright © 2015 Ludovic Courtès <ludo@gnu.org>
+;;; Copyright © 2015, 2018 Ludovic Courtès <ludo@gnu.org>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -18,12 +18,14 @@
 
 (define-module (test-gremlin)
   #:use-module (guix elf)
+  #:use-module ((guix utils) #:select (call-with-temporary-directory))
   #:use-module (guix build utils)
   #:use-module (guix build gremlin)
   #:use-module (srfi srfi-1)
   #:use-module (srfi srfi-26)
   #:use-module (srfi srfi-64)
   #:use-module (rnrs io ports)
+  #:use-module (ice-9 popen)
   #:use-module (ice-9 match))
 
 (define %guile-executable
@@ -37,6 +39,9 @@
 (define read-elf
   (compose parse-elf get-bytevector-all))
 
+(define c-compiler
+  (or (which "gcc") (which "cc") (which "g++")))
+
 
 (test-begin "gremlin")
 
@@ -63,4 +68,32 @@
          "../${ORIGIN}/bar/$ORIGIN/baz"
          "ORIGIN/foo")))
 
+(unless c-compiler
+  (test-skip 1))
+(test-equal "strip-runpath"
+  "hello\n"
+  (call-with-temporary-directory
+   (lambda (directory)
+     (with-directory-excursion directory
+       (call-with-output-file "t.c"
+         (lambda (port)
+           (display "int main () { puts(\"hello\"); }" port)))
+       (invoke c-compiler "t.c"
+               "-Wl,-rpath=/foo" "-Wl,-rpath=/bar")
+       (let* ((dyninfo (elf-dynamic-info
+                        (parse-elf (call-with-input-file "a.out"
+                                     get-bytevector-all))))
+              (old     (elf-dynamic-info-runpath dyninfo))
+              (new     (strip-runpath "a.out"))
+              (new*    (strip-runpath "a.out")))
+         (validate-needed-in-runpath "a.out")
+         (and (member "/foo" old) (member "/bar" old)
+              (not (member "/foo" new))
+              (not (member "/bar" new))
+              (equal? new* new)
+              (let* ((pipe (open-input-pipe "./a.out"))
+                     (str  (get-string-all pipe)))
+                (close-pipe pipe)
+                str)))))))
+
 (test-end "gremlin")