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# -*- 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 <>).
# Unset 'GUILE_LOAD_COMPILED_PATH' to make sure we do not stumble upon
# incompatible .go files. See
# <>.
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, 2016, 2017, 2018 Ludovic Courtès <>
;;; Copyright © 2020 Marius Bakke <>
;;; 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
;;; 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 <>.
(define-module (gnu build-support ld-wrapper)
#:use-module (srfi srfi-1)
#:use-module (ice-9 match)
#:autoload (ice-9 rdelim) (read-delimited)
#: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
;;; <> 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.
(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.
;; Allow them by default for convenience.
(let ((value (getenv "GUIX_LD_WRAPPER_ALLOW_IMPURITIES")))
(or (not value)
(let ((value (string-downcase value)))
(cond ((member value '("yes" "y" "t" "true" "1"))
((member value '("no" "n" "f" "false" "0"))
(format (current-error-port)
"ld-wrapper: ~s: invalid value for \
(define %debug?
;; Whether to emit debugging output.
(define %disable-rpath?
;; Whether to disable automatic '-rpath' addition.
(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)
(string-append (dirname file) "/" target)))
(if (>= depth %max-symlink-depth)
(lambda ()
(catch 'system-error
(lambda ()
(values #t (readlink file)))
(lambda args
(let ((errno (system-error-errno args)))
(if (or (= errno EINVAL) (= errno ENOENT))
(values #f file)
(apply throw args))))))
(lambda (success? target)
(if success?
(loop (absolute target) (+ depth 1))
(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-search-path args)
;; Return the library search path as a list of directory names. The GNU ld
;; manual notes that "[a]ll `-L' options apply to all `-l' options,
;; regardless of the order in which the options appear", so we must compute
;; the search path independently of the -l options.
(let loop ((args args)
(path '()))
(match args
(reverse path))
(("-L" directory . rest)
(loop rest (cons directory path)))
((argument . rest)
(if (string-prefix? "-L" argument) ;augment the search path
(loop rest
(cons (string-drop argument 2) path))
(loop rest path))))))
(define (library-files-linked args library-path)
;; Return the absolute file names of shared libraries explicitly linked
;; against via `-l' or with an absolute file name in ARGS, looking them up
(define files+args
(fold (lambda (argument result)
(match result
((library-files ((and flag
(or "-dynamic-linker" "-plugin"))
. rest))
;; When passed '-dynamic-linker', ignore ''; when
;; passed '-plugin', ignore
;; ''. See <>.
(list library-files
(cons* argument flag rest)))
((library-files previous-args)
(cond ((string-prefix? "-l" argument) ;add library
(let* ((lib (string-append "lib"
(string-drop argument 2)
(full (search-path library-path lib)))
(list (if full
(cons full library-files)
(cons argument previous-args))))
((and (string-prefix? %store-directory argument)
(shared-library? argument)) ;add library
(list (cons argument library-files)
(cons argument previous-args)))
(list library-files
(cons argument previous-args)))))))
(list '() '())
(match files+args
((files arguments)
(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))
(format (current-error-port)
"ld-wrapper: error: attempt to use \
library outside of ~a: ~s~%"
%store-directory file)
(exit 1)))))
(define (expand-arguments args)
;; Expand ARGS such that "response file" arguments, such as "@args.txt", are
;; expanded (info "(gcc) Overall Options").
(define (response-file-arguments file)
(define (tokenize port)
;; Return a list of all strings found in PORT. Quote characters are
;; removed, but whitespaces within quoted strings are preserved.
(let loop ((tokens '()))
(let* ((token+delimiter (read-delimited " '\"\n" port 'split))
(token (car token+delimiter))
(delim (cdr token+delimiter)))
(if (eof-object? token)
(reverse tokens)
(case delim
((#\") (loop (cons (read-delimited "\"" port) tokens)))
((#\') (loop (cons (read-delimited "'" port) tokens)))
(else (if (> (string-length token) 0)
(loop (cons token tokens))
(loop tokens))))))))
(when %debug?
(format (current-error-port)
"ld-wrapper: attempting to read arguments from '~a'~%" file))
(call-with-input-file file tokenize))
(define result
(fold-right (lambda (arg result)
(if (string-prefix? "@" arg)
(let ((file (string-drop arg 1)))
(append (catch 'system-error
(lambda ()
(response-file-arguments file))
(lambda args
;; FILE doesn't exist or cannot be read so
;; leave ARG as is.
(list arg)))
(cons arg result)))
;; If there are "@" arguments in RESULT *and* we can expand them (they don't
;; refer to nonexistent files), then recurse.
(if (equal? result args)
(expand-arguments result)))
(define (ld-wrapper . args)
;; Invoke the real `ld' with ARGS, augmented with `-rpath' switches.
(let* ((args (expand-arguments args))
(path (library-search-path args))
(libs (library-files-linked args path))
(args (append args (rpath-arguments libs))))
(when %debug?
(format (current-error-port)
"ld-wrapper: library search path: ~s~%" path)
(format (current-error-port)
"ld-wrapper: libraries linked: ~s~%" libs)
(format (current-error-port)
"ld-wrapper: invoking `~a' with ~s~%"
%real-ld args)
(force-output (current-error-port)))
(apply execl %real-ld (basename %real-ld) args)))
;;; ld-wrapper.scm ends here