Subject: Re: [bug#39807] [PATCH] guix: pack: Only wrap executable files.

From: Ludovic Courtès <[email-masked]>
Date: Wed, 21 Oct 2020 11:07:11 +0200

Hi Eric,

Eric Bavier <[email-masked]> skribis:

> In gnu/packages/aux-files/run-in-namespace.c:620-626 we try to calculate the name of the relocated store directory.  So
> far this calculation seems to "accidentaly" work:
>
> /tmp/pack-dir/gnu/store/78xrsg1z...-emacs-no-x-27.1R/bin/emacs
>              /gnu/store/w9csar3m...-emacs-no-x-27.1/bin//emacs
>
> The "R" suffix appended to the wrapper store directory name and the double-slash we get from find-files (c.f.
> guix/scripts/pack.scm:881) "cancel out".   But we might not be so fortunate and can get something like this:
>
>                           |
> /tmp/pack-dir/gnu/store/80|kbbxnz...-wrapperR/bin/hello (self)
>                 /gnu/store|/zc92ghli...-test/bin//hello (@PROG@)
>                 /gnu/store|                     (original_store)
>                           |
>
> Because the manifest entry used in the tests added in this patch enters the "else" case of `wrapped-package` (c.f.
> guix/scripts/pack.scm:904) the index calculation strays and we get a non-directory mount point.  I can make the test
> pass by using a slightly longer name of "testing" for the file-union :)
>
> I don't think we can enforce a stricter match between the wrapper and target store item names to ensure their lengths
> are the same, right?  It seems like we maybe want to ignore @WRAPPED_PROGRAM@ and use only /proc/self/exe and
> original_store to find the relocated store directory?  A regex search might be too costly.  We could use strstr to
> search for the first occurrence of original_store, if we don't mind assuming that most people will probably not unpack
> into $HOME/.guix/gnu/store/mine/packs/foo e.g.

Good catch!  This is embarrassing.

Instead of searching for an occurrence of ORIGINAL_STORE, can’t we use
the file name of the wrapper (as opposed to WRAPPED_PROGRAM) in the
index calculation?  Along these lines:

diff --git a/gnu/packages/aux-files/run-in-namespace.c b/gnu/packages/aux-files/run-in-namespace.c
index 52a16a5362..947ff02dda 100644
--- a/gnu/packages/aux-files/run-in-namespace.c
+++ b/gnu/packages/aux-files/run-in-namespace.c
@@ -620,7 +620,7 @@ main (int argc, char *argv[])
   /* SELF is something like "/home/ludo/.local/gnu/store/…-foo/bin/ls" and we
      want to extract "/home/ludo/.local/gnu/store".  */
   size_t index = strlen (self)
-    - strlen ("@WRAPPED_PROGRAM@") + strlen (original_store);
+    - strlen (WRAPPER_PROGRAM) + strlen (original_store);
   char *store = strdup (self);
   store[index] = '\0';
 
diff --git a/guix/scripts/pack.scm b/guix/scripts/pack.scm
index a5a70d5162..c353f50ced 100644
--- a/guix/scripts/pack.scm
+++ b/guix/scripts/pack.scm
@@ -856,6 +856,7 @@ last resort for relocation."
               (mkdir-p (dirname result))
               (apply invoke #$compiler "-std=gnu99" "-static" "-Os" "-g0" "-Wall"
                      "run.c" "-o" result
+                     (string-append "-DWRAPPER_PROGRAM=\"" result "\"")
                      (append (if proot
                                  (list (string-append "-DPROOT_PROGRAM=\""
                                                       proot "\""))

Thanks,
Ludo’.