[PATCH, AArch64] Detect assembler vector mov parsing bug

[Richard Henderson]

The strchr implementation that was recently committed to mainline tickles an
assembler bug fixed by

commit 8db49cc2de52033990ae5d4d6aacedc8f986e803
Author: Will Newton <will.newton@linaro.org>
Date:   Thu Oct 31 17:21:11 2013 -0700

    config/tc-aarch64.c: Avoid trying to parse a vector mov as immediate.
    ...

Obviously not a problem with a relatively new binutils installed, but Carlos
ran into this problem building mainline glibc on a system using binutils 2.23.

It's not a silent error (we die linking ld.so), but its somewhat cryptic.
Carlos opined to me that we ought to error out at configure time with an
understandable message.

Rather than check for version numbers, let's check for functionality.

Ok?


r~
-------------- next part --------------
	* sysdeps/aarch64/configure.ac: Check for assembler mov bug.
	* sysdeps/aarch64/configure: Regenerate.

diff --git a/sysdeps/aarch64/configure.ac b/sysdeps/aarch64/configure.ac
index 7851dd4..6654684 100644
--- a/sysdeps/aarch64/configure.ac
+++ b/sysdeps/aarch64/configure.ac
@@ -20,3 +20,19 @@ if test $libc_cv_aarch64_be = yes; then
 else
   LIBC_CONFIG_VAR([default-abi], [lp64])
 fi
+
+# Check to see if the assembler has fixed a parsing bug wrt vector "mov"
+# instructions leading to undefined symbols.
+AC_MSG_CHECKING([for assembler vector mov bug])
+old_LDFLAGS="$LDFLAGS"
+LDFLAGS="$LDFLAGS -nostdlib -nostartfiles"
+AC_LINK_IFELSE([[void _start(void) { asm("mov x0,v0.2d[0]"); }]],
+  [AC_MSG_RESULT([no])],
+  [AC_MSG_RESULT([yes])
+   AC_MSG_ERROR(
+[*** Version of binutils is too old to support AArch64.
+*** Your version of binutils contains a bug in the handling
+*** of vector names. Please upgrade to a version of binutils
+*** that contains commit:
+*** 8db49cc2de52033990ae5d4d6aacedc8f986e803])])
+LDFLAGS="$old_LDFLAGS"