Subject: [PATCH core-updates] gnu: glibc-final: Catch all cases of a glibc user not requesting 64-bit offsets and then using readdir.

From: Danny Milosavljevic <[email-masked]>
Date: Thu, 24 Sep 2020 16:12:11 +0200

* gnu/packages/commencement.scm (glibc-final): Catch all cases of a glibc user not
requesting 64-bit offsets and then using readdir.
---
 gnu/packages/commencement.scm | 52 ++++++++++++++++++++++++++++++++++-
 1 file changed, 51 insertions(+), 1 deletion(-)

diff --git a/gnu/packages/commencement.scm b/gnu/packages/commencement.scm
index e5a4caa95c..5a62c9df3a 100644
--- a/gnu/packages/commencement.scm
+++ b/gnu/packages/commencement.scm
@@ -3462,7 +3462,57 @@ exec ~a/bin/~a-~a -B~a/lib -Wl,-dynamic-linker -Wl,~a/~a \"$@\"~%"
                ,hurd-headers-boot0)
              '())
        ,@(package-outputs glibc-final-with-bootstrap-bash))
-      ,@(package-arguments glibc-final-with-bootstrap-bash)))))
+      ,@(substitute-keyword-arguments
+         (package-arguments glibc-final-with-bootstrap-bash)
+         ((#:phases phases)
+          `(modify-phases ,phases
+             (add-after 'unpack 'patch-dirent
+               (lambda* (#:key outputs #:allow-other-keys)
+                 ;; QEMU transparent emulation is in somewhat of a pickle sometimes.
+                 ;; There is no support in the kernel syscalls of specifying what
+                 ;; kind of userspace you are emulating.  Some parts of the
+                 ;; structures passed back-and-forth between kernel and guest
+                 ;; userspace can change size (including size of individual fields).
+                 ;;
+                 ;; One of the affected structures is "struct dirent".  The ext4
+                 ;; file system puts a 64 bit hash into "d_off" on the kernel side.
+                 ;; If the guest system's glibc is 32 bit it is going to be very
+                 ;; confused (it does check whether d_off fits into the structure
+                 ;; it gives back to the user--and it doesn't fit.  Hence readdir
+                 ;; fails).
+                 ;; This manifests itself in simple directory reads not working
+                 ;; anymore in parts of cmake, for example.
+                 ;;
+                 ;; There is a very simple and complete way to avoid this problem:
+                 ;; Just always use 64 bit offsets in user space programs (also
+                 ;; on 32 bit machines).
+                 ;;
+                 ;; Note: We might want to avoid using 64 bit when bootstrapping
+                 ;; using mescc (since mescc doesn't directly support 64 bit
+                 ;; values)--but then bootstrapping has to be done on a
+                 ;; file system other than ext4, or on ext4 with the feature
+                 ;; "dir_index" disabled.
+                 ;;
+                 ;; The change below does not affect 64 bit users.
+                 ;;
+                 ;; See <https://issues.guix.gnu.org/43513>.
+                 (let ((port (open-file "include/dirent.h" "a")))
+                   (display "
+#if __SIZEOF_LONG__ < 8
+#ifndef __USE_FILE_OFFSET64
+#undef readdir
+#define readdir @READDIR_WITHOUT_FILE_OFFSET64_IS_A_REALLY_BAD_IDEA@
+#endif
+#endif
+" port)
+                   (close-port port))
+                 ;; This file includes <dirent.h> and thus checks sanity already.
+                 ;; TODO: Check dirent/scandir-tail.c, dirent/scandir64-tail.c.
+                 (substitute* "posix/glob.c"
+                  (("(#[ ]*define[ ][ ]*readdir)") "
+#undef readdir
+#define readdir"))
+                 #t)))))))))
 
 (define/system-dependent gcc-boot0-wrapped
   ;; Make the cross-tools GCC-BOOT0 and BINUTILS-BOOT0 available under the