See https://github.com/thepowersgang/mrustc/archive/v0.8.0.tar.gz

--- rustc-1.19.0-src-orig/src/libcore/intrinsics.rs
+++ rustc-1.19.0-src/src/libcore/intrinsics.rs
@@ -678,5 +678,9 @@
     pub fn min_align_of_val<T: ?Sized>(_: &T) -> usize;
 
+    /// Obtain the length of a slice pointer
+    #[cfg(rust_compiler="mrustc")]
+    pub fn mrustc_slice_len<T>(pointer: *const [T]) -> usize;
+
     /// Gets a static string slice containing the name of a type.
     pub fn type_name<T: ?Sized>() -> &'static str;

--- rustc-1.19.0-src-orig/src/libcore/slice/mod.rs
+++ rustc-1.19.0-src/src/libcore/slice/mod.rs
@@ -413,6 +413,8 @@
     #[inline]
     fn len(&self) -> usize {
-        unsafe {
-            mem::transmute::<&[T], Repr<T>>(self).len
-        }
+        #[cfg(not(rust_compiler="mrustc"))]
+        let rv = unsafe { mem::transmute::<&[T], Repr<T>>(self).len };
+        #[cfg(rust_compiler="mrustc")]
+        let rv = unsafe { ::intrinsics::mrustc_slice_len(self) };
+        rv
     }
ble>
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<div class='path'>path: <a href='/guix/log/?id=a33f036064531d36da8dc632fdb63850e1cac0fd'>root</a>/<a href='/guix/log/tests?id=a33f036064531d36da8dc632fdb63850e1cac0fd'>tests</a>/<a href='/guix/log/tests/guix-archive.sh?id=a33f036064531d36da8dc632fdb63850e1cac0fd'>guix-archive.sh</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/tests/guix-archive.sh?id=a33f036064531d36da8dc632fdb63850e1cac0fd&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2020-12-15 17:32:09 +0100'>2020-12-15</span></td><td><a href='/guix/commit/tests/guix-archive.sh?id=ed7d02f7c198970ce3fe94bcee47592963326446'>serialization: 'restore-file' sets canonical timestamp and permissions.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-09-28 21:06:36 -0500'>2020-09-28</span></td><td><a href='/guix/commit/tests/guix-archive.sh?id=d8934360d2453a403b5433e71d09188e4ed23b57'>tests: Simplify shell exit status negation;</a><span class='msg-avail'>...</span></td><td>Eric Bavier</td></tr>
<tr><td><span title='2019-12-12 17:56:58 +0100'>2019-12-12</span></td><td><a href='/guix/commit/tests/guix-archive.sh?id=044277f610b02c3821afa0afdc2b2b140bb92cb4'>guix archive: Add '--list'.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>