See <http://lists.gnu.org/archive/html/bug-patch/2015-06/msg00009.html>

From 0507dfad5f060161f01840067e1bb1615257b636 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ludovic=20Court=C3=A8s?= <ludo@gnu.org>
Date: Mon, 8 Jun 2015 17:27:56 +0200
Subject: [PATCH] Do not rely on PATH_MAX when reading a symlink target.

* src/util.c (move_file, copy_file): Use 'fromst->st_size + 1' and
'tost->st_size + 1' for the allocation, and 'fromst->st_size' and
'tost->st_size' instead of PATH_MAX.  Fixes compilation on GNU/Hurd.
---
 src/util.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/src/util.c b/src/util.c
index 1cc08ba..67dbd3a 100644
--- a/src/util.c
+++ b/src/util.c
@@ -460,12 +460,12 @@ move_file (char const *from, bool *from_needs_removal,
 
 	  /* FROM contains the contents of the symlink we have patched; need
 	     to convert that back into a symlink. */
-	  char *buffer = xmalloc (PATH_MAX);
+	  char *buffer = xmalloc (fromst->st_size + 1);
 	  int fd, size = 0, i;
 
 	  if ((fd = safe_open (from, O_RDONLY | O_BINARY, 0)) < 0)
 	    pfatal ("Can't reopen file %s", quotearg (from));
-	  while ((i = read (fd, buffer + size, PATH_MAX - size)) > 0)
+	  while ((i = read (fd, buffer + size, fromst->st_size - size)) > 0)
 	    size += i;
 	  if (i != 0 || close (fd) != 0)
 	    read_fatal ();
@@ -610,10 +610,10 @@ copy_file (char const *from, char const *to, struct stat *tost,
 
   if (S_ISLNK (mode))
     {
-      char *buffer = xmalloc (PATH_MAX + 1);
+      char *buffer = xmalloc (tost->st_size + 1);
       ssize_t r;
 
-      if ((r = safe_readlink (from, buffer, PATH_MAX)) < 0)
+      if ((r = safe_readlink (from, buffer, tost->st_size)) < 0)
 	pfatal ("Can't read %s %s", "symbolic link", from);
       buffer[r] = '\0';
       if (safe_symlink (buffer, to) != 0)
-- 
2.16.2

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<div class='path'>path: <a href='/guix/log/?id=b4ce58746ee46034c6bcc514db3dbec017b1a243'>root</a>/<a href='/guix/log/gnu?id=b4ce58746ee46034c6bcc514db3dbec017b1a243'>gnu</a>/<a href='/guix/log/gnu/packages?id=b4ce58746ee46034c6bcc514db3dbec017b1a243'>packages</a>/<a href='/guix/log/gnu/packages/debian.scm?id=b4ce58746ee46034c6bcc514db3dbec017b1a243'>debian.scm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/gnu/packages/debian.scm?id=b4ce58746ee46034c6bcc514db3dbec017b1a243&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2022-02-16 09:59:29 +0200'>2022-02-16</span></td><td><a href='/guix/commit/gnu/packages/debian.scm?id=34755d912efd29d4c1118b318a4096fb8a65005d'>gnu: debian-ports-archive-keyring: Update to 2022.02.15.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/debian.scm (debian-ports-archive-keyring): Update to 2022.02.15.
</span></span></td><td>Efraim Flashner</td></tr>
<tr><td><span title='2022-01-12 16:08:11 +0200'>2022-01-12</span></td><td><a href='/guix/commit/gnu/packages/debian.scm?id=9e3b4d69dae190a7c2bd670e5f42ca6a522c5708'>gnu: debian-ports-archive-keyring: Update to 2021.12.30.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/debian.scm (debian-ports-archive-keyring): Update to 2021.12.30.
</span></span></td><td>Efraim Flashner</td></tr>
<tr><td><span title='2021-12-16 16:27:03 +0100'>2021-12-16</span></td><td><a href='/guix/commit/gnu/packages/debian.scm?id=12e9687eb925eff12200f86c479344261203a464'>gnu: dpkg: Update to 1.21.0.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/debian.scm (dpkg): Update to 1.21.0.
[arguments]: Don't explicitly return #t from phases.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2021-12-13 22:15:07 +0100'>2021-12-13</span></td><td><a href='/guix/commit/gnu/packages/debian.scm?id=e3196755e60ba7f1ed9d432e73f26a85e0c8893c'>gnu: Further simplify package inputs.</a><span class='msg-avail'>...<span class='msg-tooltip'>This is the result of running:

  ./pre-inst-env guix style --input-simplification=safe

and manually undoing changes on a dozen of packages to reduce
rebuilds (derivations for emacs, icecat, and libreoffice are unchanged.)
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2021-12-13 17:48:25 +0100'>2021-12-13</span></td><td><a href='/guix/commit/gnu/packages/debian.scm?id=8394619baceb118df92e355377fd543bb1aa501a'>gnu: Simplify package inputs.</a><span class='msg-avail'>...<span class='msg-tooltip'>This commit was obtained by running:

  ./pre-inst-env guix style

without any additional argument.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2021-11-09 08:48:49 +0200'>2021-11-09</span></td><td><a href='/guix/commit/gnu/packages/debian.scm?id=4d03acbb02a1f8bdb03dd986f34ddfe7de3d827c'>gnu: debianutils: Update to 5.5-1.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/debian.scm (debianutils): Update to 5.5-1.
[arguments]: Remove custom 'create-translations phase.
</span></span></td><td>Efraim Flashner</td></tr>
<tr><td><span title='2021-11-09 08:48:35 +0200'>2021-11-09</span></td><td><a href='/guix/commit/gnu/packages/debian.scm?id=1b95a7b2b187dd8b8b996628c7651c8c08593249'>gnu: debootstrap: Update to 1.0.126.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/debian.scm (debootstrap): Update to 1.0.126.
</span></span></td><td>Efraim Flashner</td></tr>
<tr><td><span title='2021-10-10 16:12:46 +0300'>2021-10-10</span></td><td><a href='/guix/commit/gnu/packages/debian.scm?id=6cb8c0052ed6490fdf2fdd487569c04f32758686'>gnu: Add debian-ports-archive-keyring: New variable.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/debian.scm (debian-ports-archive-keyring): New variable.
</span></span></td><td>Efraim Flashner</td></tr>