hurd: break relocation loop between libc.so and lib{mach,hurd}user.so

See
https://sourceware.org/pipermail/libc-alpha/2020-November/119575.html

lib{mach,hurd}user.so gets relocated before libc.so, but its references
to strpcpy and memcpy would need an ifunc decision, which e.g. on
x86 relies on cpu_features, but libc.so's _rtld_global_ro is not
relocated yet.

We can however just make lib{mach,hurd}user.so only call non-ifunc
functions, which can be relocated before libc.so is relocated.

mach/Makefile

@@ -25,7 +25,7 @@ headers = mach_init.h mach.h mach_error.h mach-shortcuts.h mach/mach_traps.h \
 lock = spin-solid spin-lock mutex-init mutex-solid
 lock-headers = lock-intern.h spin-lock.h
 routines = $(mach-syscalls) $(mach-shortcuts) \
-	   mach_init mig_strncpy msg \
+	   mach_init mig_strncpy mig_memcpy msg \
 	   mig-alloc mig-dealloc mig-reply \
 	   msg-destroy msgserver \
 	   mach_error errstring error_compat errsystems \

mach/Versions

@@ -68,4 +68,8 @@ libc {
     __spin_lock; __spin_lock_init; __spin_lock_solid; __spin_try_lock;
     __spin_unlock;
   }
+  GLIBC_PRIVATE {
+    # functions used by RPC stubs
+    __mig_memcpy;
+  }
 }

mach/mach/mig_support.h

@@ -54,19 +54,6 @@ extern void mig_reply_setup (const mach_msg_header_t *__request,
 extern vm_size_t mig_strncpy (char *__dst, const char *__src, vm_size_t __len);
 extern vm_size_t __mig_strncpy (char *__dst, const char *__src, vm_size_t);
 
-#if defined __USE_EXTERN_INLINES && defined _LIBC
+extern void *__mig_memcpy (void *__dst, const void *__src, vm_size_t __len);
-__extern_inline vm_size_t
-__mig_strncpy (char *__dst, const char *__src, vm_size_t __len)
-{
-  return __stpncpy (__dst, __src, __len) - __dst;
-}
-__extern_inline vm_size_t
-mig_strncpy (char *__dst, const char *__src, vm_size_t __len)
-{
-  return __mig_strncpy (__dst, __src, __len);
-}
-#endif
-
-
 
 #endif	/* mach/mig_support.h */

mach/mig_memcpy.c

@@ -0,0 +1,26 @@
+/* memcpy stub for mig stubs in libmachuser and libhurduser.
+   Copyright (C) 2020 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <mach.h>
+#include <string.h>
+
+void *
+__mig_memcpy (void *dst, const void *src, vm_size_t len)
+{
+  return memcpy (dst, src, len);
+}

sysdeps/mach/include/mach/mig_support.h

@@ -4,5 +4,17 @@
 libc_hidden_proto (__mig_get_reply_port)
 libc_hidden_proto (__mig_dealloc_reply_port)
 libc_hidden_proto (__mig_init)
+
+#ifdef _LIBC
+# include <libc-symbols.h>
+
+# if defined USE_MULTIARCH && (IS_IN (libmachuser) || IS_IN (libhurduser))
+/* Avoid directly calling ifunc-enabled memcpy or strpcpy,
+   because they would introduce a relocation loop between lib*user and
+   libc.so.  */
+#  define memcpy(dest, src, n) __mig_memcpy(dest, src, n)
+# endif
+#endif
+
 #endif
 #endif