Source: emacs24
Version: 24.5+1-6
Severity: wishlist
Tags: patch upstream
User: reproducible-builds@lists.alioth.debian.org
Usertags: toolchain
X-Debbugs-Cc: reproducible-builds@lists.alioth.debian.org
Dear Maintainer,
When bytecompiling elisp files, cl-gensym-counter is initialized from
the current time, leading to unreproducible results. This can affect
reproducibility [1] of some software packages that build-depend on emacs
(and of emacs24 itself). I suggest to set the initial value of
cl-gensym-counter from the names of the files to be compiled (see
proposed patch).
Test-case:
cd /tmp
wget
https://sources.debian.net/data/main/e/emacs24/24.5+1-5/lisp/org/ob-C.el
emacs -batch --no-site-file --no-site-lisp -f batch-byte-compile ob-C.el
cp ob-C.elc ob-C.elc.0
sleep 1
emacs -batch --no-site-file --no-site-lisp -f batch-byte-compile ob-C.el
diff ob-C.elc ob-C.elc.0
The two files should be the same, but they differ (with different #:Gnnn
values)
Regards,
Alexis Bienvenüe.
[1] https://wiki.debian.org/ReproducibleBuilds/
Description: Reproducible gensym-counter
When calling batch-byte-compile, set the start value of gensym-counter from
a hash of the command-line arguments instead of time, so that the compiled
files can be reproducible.
Author: Alexis Bienvenüe <p...@passoire.fr>
Index: emacs24-24.5+1/lisp/emacs-lisp/bytecomp.el
===================================================================
--- emacs24-24.5+1.orig/lisp/emacs-lisp/bytecomp.el
+++ emacs24-24.5+1/lisp/emacs-lisp/bytecomp.el
@@ -4625,6 +4625,10 @@ already up-to-date."
(if (not noninteractive)
(error "`batch-byte-compile' is to be used only with -batch"))
(let ((error nil))
+ ;; Init gensym-counter from command-line arguments instead of
+ ;; time, to get a reproducible result.
+ (cl-init-gensym-counter
+ (mapconcat 'identity (sort command-line-args-left 'string<) ";"))
(while command-line-args-left
(if (file-directory-p (expand-file-name (car command-line-args-left)))
;; Directory as argument.
Index: emacs24-24.5+1/lisp/emacs-lisp/cl-lib.el
===================================================================
--- emacs24-24.5+1.orig/lisp/emacs-lisp/cl-lib.el
+++ emacs24-24.5+1/lisp/emacs-lisp/cl-lib.el
@@ -261,6 +261,12 @@ so that they are registered at compile-t
(defvar cl--gensym-counter (* (logand (cl--random-time) 1023) 100))
+(defun cl-init-gensym-counter (string)
+ "Set gensym-counter from a hash of string."
+ (setq cl--gensym-counter (* (logand
+ (string-to-number (substring (secure-hash 'sha1 string) -3) 16)
+ 1023) 100)))
+
;;; Numbers.
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