Re: 18/36: services: hurd: Add dummy loopback.

["Ludovic Courtès" <ludo@gnu.org>]

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Hi,

Jan Nieuwenhuizen <janneke@gnu.org> skribis:

>> Could it be ‘ifreq-struct-size’ that’s off on GNU/Hurd, or one of its
>> friends?
>
> Something like that: sizeof-ifconf is set to 16 (like on x86_64), but
> it's size should be 8.

Oh, that’s because ‘define-c-struct’ does all the work at
macro-expansion time, with the host types and alignment constraints.  I
wonder how we didn’t notice it earlier.  Cross-compiling from x86_64 to
ARMv7 has the same problem, but maybe the networking ioctls work by
chance.

The patch below appears to fix it:

--8<---------------cut here---------------start------------->8---
$ ./pre-inst-env guild compile --target=i686-pc-linux-gnu guix/build/syscalls.scm -o guix/build/syscalls.go
wrote `guix/build/syscalls.go'
$ guix environment -s i686-linux -C --ad-hoc guile-next -- guile -L . -C .
GNU Guile 3.0.2
Copyright (C) 1995-2020 Free Software Foundation, Inc.

Guile comes with ABSOLUTELY NO WARRANTY; for details type `,show w'.
This program is free software, and you are welcome to redistribute it
under certain conditions; type `,show c' for details.

Enter `,help' for help.
scheme@(guile-user)> ,use(guix build syscalls)
scheme@(guile-user)> ,m(guix build syscalls)
scheme@(guix build syscalls)> sizeof-ifconf
$1 = 8
scheme@(guix build syscalls)> %host-type
$2 = "i686-unknown-linux-gnu"
--8<---------------cut here---------------end--------------->8---

Thank you!

Ludo’.


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diff --git a/guix/build/syscalls.scm b/guix/build/syscalls.scm
index 73b439fb7d..00d8ceb480 100644
--- a/guix/build/syscalls.scm
+++ b/guix/build/syscalls.scm
@@ -23,6 +23,7 @@
 
 (define-module (guix build syscalls)
   #:use-module (system foreign)
+  #:use-module (system base target)
   #:use-module (rnrs bytevectors)
   #:autoload   (ice-9 binary-ports) (get-bytevector-n)
   #:use-module (srfi srfi-1)
@@ -194,9 +195,14 @@
      (* (sizeof* type) n))
     ((_ type)
      (let-syntax ((v (lambda (s)
-                       (let ((val (sizeof type)))
-                         (syntax-case s ()
-                           (_ val))))))
+                       ;; When compiling natively, call 'sizeof' at expansion
+                       ;; time; otherwise, emit code to call it at run time.
+                       (syntax-case s ()
+                         (_
+                          (if (= (target-word-size)
+                                 (with-target %host-type target-word-size))
+                              (sizeof type)
+                              #'(sizeof type)))))))
        v))))
 
 (define-syntax alignof*
@@ -208,9 +214,14 @@
      (alignof* type))
     ((_ type)
      (let-syntax ((v (lambda (s)
-                       (let ((val (alignof type)))
-                         (syntax-case s ()
-                           (_ val))))))
+                       ;; When compiling natively, call 'sizeof' at expansion
+                       ;; time; otherwise, emit code to call it at run time.
+                       (syntax-case s ()
+                         (_
+                          (if (= (target-word-size)
+                                 (with-target %host-type target-word-size))
+                              (alignof type)
+                              #'(alignof type)))))))
        v))))
 
 (define-syntax align                             ;as found in (system foreign)