x86: fix Autoconf caching of instruction support checks [BZ #27991]

The Autoconf documentation for the AC_CACHE_CHECK macro states:

  The commands-to-set-it must have no side effects except for setting
  the variable cache-id, see below.

However, the tests for support of -msahf and -mmovbe were embedded in
the commands-to-set-it for lib_cv_include_x86_isa_level. This had the
consequence that libc_cv_have_x86_lahf_sahf and libc_cv_have_x86_movbe
were not defined whenever lib_cv_include_x86_isa_level was read from
cache. These variables' being undefined meant that their unquoted use
in later test expressions led to the 'test' built-in's misparsing its
arguments and emitting errors like "test: =: unexpected operator" or
"test: =: unary operator expected", depending on the particular shell.

This commit refactors the tests for LAHF/SAHF and MOVBE instruction
support into their own AC_CACHE_CHECK macro invocations to obey the
rule that the commands-to-set-it must have no side effects other than
setting the variable named by cache-id.

Signed-off-by: Matt Whitlock <sourceware@mattwhitlock.name>
Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

2 files changed, 53 insertions, 37 deletions

diff --git a/sysdeps/x86/configure b/sysdeps/x86/configure
index ead1295c38..62676bb686 100644
--- a/sysdeps/x86/configure
+++ b/sysdeps/x86/configure
@@ -126,8 +126,6 @@ cat > conftest2.S <<EOF
 4:
 EOF
 libc_cv_include_x86_isa_level=no
-libc_cv_have_x86_lahf_sahf=no
-libc_cv_have_x86_movbe=no
 if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS -nostartfiles -nostdlib -r -o conftest conftest1.S conftest2.S'
   { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
   (eval $ac_try) 2>&5
@@ -137,9 +135,22 @@ if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS -nostartfiles -nostdlib -r -o conftest c
   count=`LC_ALL=C $READELF -n conftest | grep NT_GNU_PROPERTY_TYPE_0 | wc -l`
   if test "$count" = 1; then
     libc_cv_include_x86_isa_level=yes
-    cat > conftest.c <<EOF
-EOF
-    if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS -fverbose-asm -S -o - conftest.c'
+  fi
+fi
+rm -f conftest*
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_include_x86_isa_level" >&5
+$as_echo "$libc_cv_include_x86_isa_level" >&6; }
+if test $libc_cv_include_x86_isa_level = yes; then
+  $as_echo "#define INCLUDE_X86_ISA_LEVEL 1" >>confdefs.h
+
+  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for LAHF/SAHF instruction support" >&5
+$as_echo_n "checking for LAHF/SAHF instruction support... " >&6; }
+if ${libc_cv_have_x86_lahf_sahf+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+      libc_cv_have_x86_lahf_sahf=no
+    if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS -fverbose-asm -S -o - -x c /dev/null'
   { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
   (eval $ac_try) 2>&5
   ac_status=$?
@@ -147,7 +158,20 @@ EOF
   test $ac_status = 0; }; } | grep -q "\-msahf"; then
       libc_cv_have_x86_lahf_sahf=yes
     fi
-    if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS -fverbose-asm -S -o - conftest.c'
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_have_x86_lahf_sahf" >&5
+$as_echo "$libc_cv_have_x86_lahf_sahf" >&6; }
+  if test $libc_cv_have_x86_lahf_sahf = yes; then
+    $as_echo "#define HAVE_X86_LAHF_SAHF 1" >>confdefs.h
+
+  fi
+  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for MOVBE instruction support" >&5
+$as_echo_n "checking for MOVBE instruction support... " >&6; }
+if ${libc_cv_have_x86_movbe+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+      libc_cv_have_x86_movbe=no
+    if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS -fverbose-asm -S -o - -x c /dev/null'
   { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
   (eval $ac_try) 2>&5
   ac_status=$?
@@ -155,23 +179,13 @@ EOF
   test $ac_status = 0; }; } | grep -q "\-mmovbe"; then
       libc_cv_have_x86_movbe=yes
     fi
-  fi
-fi
-rm -f conftest*
-fi
-{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_include_x86_isa_level" >&5
-$as_echo "$libc_cv_include_x86_isa_level" >&6; }
-if test $libc_cv_include_x86_isa_level = yes; then
-  $as_echo "#define INCLUDE_X86_ISA_LEVEL 1" >>confdefs.h
-
 fi
-if test $libc_cv_have_x86_lahf_sahf = yes; then
-  $as_echo "#define HAVE_X86_LAHF_SAHF 1" >>confdefs.h
-
-fi
-if test $libc_cv_have_x86_movbe = yes; then
-  $as_echo "#define HAVE_X86_MOVBE 1" >>confdefs.h
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_have_x86_movbe" >&5
+$as_echo "$libc_cv_have_x86_movbe" >&6; }
+  if test $libc_cv_have_x86_movbe = yes; then
+    $as_echo "#define HAVE_X86_MOVBE 1" >>confdefs.h
 
+  fi
 fi
 config_vars="$config_vars
 enable-x86-isa-level = $libc_cv_include_x86_isa_level"
diff --git a/sysdeps/x86/configure.ac b/sysdeps/x86/configure.ac
index bca97fdc2f..04a12ab680 100644
--- a/sysdeps/x86/configure.ac
+++ b/sysdeps/x86/configure.ac
@@ -98,30 +98,32 @@ cat > conftest2.S <<EOF
 4:
 EOF
 libc_cv_include_x86_isa_level=no
-libc_cv_have_x86_lahf_sahf=no
-libc_cv_have_x86_movbe=no
 if AC_TRY_COMMAND(${CC-cc} $CFLAGS $CPPFLAGS -nostartfiles -nostdlib -r -o conftest conftest1.S conftest2.S); then
   count=`LC_ALL=C $READELF -n conftest | grep NT_GNU_PROPERTY_TYPE_0 | wc -l`
   if test "$count" = 1; then
     libc_cv_include_x86_isa_level=yes
-    cat > conftest.c <<EOF
-EOF
-    if AC_TRY_COMMAND(${CC-cc} $CFLAGS $CPPFLAGS -fverbose-asm -S -o - conftest.c) | grep -q "\-msahf"; then
-      libc_cv_have_x86_lahf_sahf=yes
-    fi
-    if AC_TRY_COMMAND(${CC-cc} $CFLAGS $CPPFLAGS -fverbose-asm -S -o - conftest.c) | grep -q "\-mmovbe"; then
-      libc_cv_have_x86_movbe=yes
-    fi
   fi
 fi
 rm -f conftest*])
 if test $libc_cv_include_x86_isa_level = yes; then
   AC_DEFINE(INCLUDE_X86_ISA_LEVEL)
-fi
-if test $libc_cv_have_x86_lahf_sahf = yes; then
-  AC_DEFINE(HAVE_X86_LAHF_SAHF)
-fi
-if test $libc_cv_have_x86_movbe = yes; then
-  AC_DEFINE(HAVE_X86_MOVBE)
+  AC_CACHE_CHECK([for LAHF/SAHF instruction support],
+		 libc_cv_have_x86_lahf_sahf, [dnl
+    libc_cv_have_x86_lahf_sahf=no
+    if AC_TRY_COMMAND(${CC-cc} $CFLAGS $CPPFLAGS -fverbose-asm -S -o - -x c /dev/null) | grep -q "\-msahf"; then
+      libc_cv_have_x86_lahf_sahf=yes
+    fi])
+  if test $libc_cv_have_x86_lahf_sahf = yes; then
+    AC_DEFINE(HAVE_X86_LAHF_SAHF)
+  fi
+  AC_CACHE_CHECK([for MOVBE instruction support],
+		 libc_cv_have_x86_movbe, [dnl
+    libc_cv_have_x86_movbe=no
+    if AC_TRY_COMMAND(${CC-cc} $CFLAGS $CPPFLAGS -fverbose-asm -S -o - -x c /dev/null) | grep -q "\-mmovbe"; then
+      libc_cv_have_x86_movbe=yes
+    fi])
+  if test $libc_cv_have_x86_movbe = yes; then
+    AC_DEFINE(HAVE_X86_MOVBE)
+  fi
 fi
 LIBC_CONFIG_VAR([enable-x86-isa-level], [$libc_cv_include_x86_isa_level])