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authorSzabolcs Nagy <szabolcs.nagy@arm.com>2020-05-06 20:22:16 +0100
committerSzabolcs Nagy <szabolcs.nagy@arm.com>2020-06-12 14:34:39 +0100
commit088a606441f624221ce9be2038b71ca908f40c42 (patch)
treea00ca09d17cfbf8799f2534280681b12ee486518
parentd9c9571877f750e62b330753ede6bd9c5d79c84b (diff)
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aarch64: configure test for BTI support
Check BTI support in the compiler and linker.  The check also
requires READELF that understands the BTI GNU property note.
It is expected to succeed with gcc >=gcc-9 configured with
--enable-standard-branch-protection and binutils >=binutils-2.33.

Note: passing -mbranch-protection=bti in CFLAGS when building glibc
may not be enough to get a glibc that supports BTI because crtbegin*
and crtend* provided by the compiler needs to be BTI compatible too.
-rw-r--r--config.h.in3
-rw-r--r--sysdeps/aarch64/configure42
-rw-r--r--sysdeps/aarch64/configure.ac19
3 files changed, 64 insertions, 0 deletions
diff --git a/config.h.in b/config.h.in
index 831eca2fe1..67169e5d01 100644
--- a/config.h.in
+++ b/config.h.in
@@ -109,6 +109,9 @@
 /* AArch64 big endian ABI */
 #undef HAVE_AARCH64_BE
 
+/* AArch64 BTI support enabled.  */
+#define HAVE_AARCH64_BTI 0
+
 /* C-SKY ABI version.  */
 #undef CSKYABI
 
diff --git a/sysdeps/aarch64/configure b/sysdeps/aarch64/configure
index 5bd355a691..70477a7fa5 100644
--- a/sysdeps/aarch64/configure
+++ b/sysdeps/aarch64/configure
@@ -172,3 +172,45 @@ else
   config_vars="$config_vars
 default-abi = lp64"
 fi
+
+# Only consider BTI supported if -mbranch-protection=bti is
+# on by default in the compiler and the linker produces
+# binaries with GNU property notes in PT_GNU_PROPERTY segment.
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for BTI support" >&5
+$as_echo_n "checking for BTI support... " >&6; }
+if ${libc_cv_aarch64_bti+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+    cat > conftest.c <<EOF
+void foo (void) { }
+EOF
+  libc_cv_aarch64_bti=no
+  if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS -nostdlib -nostartfiles $no_ssp -shared -fPIC -o conftest.so conftest.c'
+  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
+  (eval $ac_try) 2>&5
+  ac_status=$?
+  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
+  test $ac_status = 0; }; } \
+     && { ac_try='$READELF -lW conftest.so | grep -q GNU_PROPERTY'
+  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
+  (eval $ac_try) 2>&5
+  ac_status=$?
+  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
+  test $ac_status = 0; }; } \
+     && { ac_try='$READELF -nW conftest.so | grep -q "NT_GNU_PROPERTY_TYPE_0.*AArch64 feature:.* BTI"'
+  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
+  (eval $ac_try) 2>&5
+  ac_status=$?
+  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
+  test $ac_status = 0; }; }
+  then
+    libc_cv_aarch64_bti=yes
+  fi
+  rm -rf conftest.*
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_aarch64_bti" >&5
+$as_echo "$libc_cv_aarch64_bti" >&6; }
+if test $libc_cv_aarch64_bti = yes; then
+  $as_echo "#define HAVE_AARCH64_BTI 1" >>confdefs.h
+
+fi
diff --git a/sysdeps/aarch64/configure.ac b/sysdeps/aarch64/configure.ac
index 7851dd4dac..798f494740 100644
--- a/sysdeps/aarch64/configure.ac
+++ b/sysdeps/aarch64/configure.ac
@@ -20,3 +20,22 @@ if test $libc_cv_aarch64_be = yes; then
 else
   LIBC_CONFIG_VAR([default-abi], [lp64])
 fi
+
+# Only consider BTI supported if -mbranch-protection=bti is
+# on by default in the compiler and the linker produces
+# binaries with GNU property notes in PT_GNU_PROPERTY segment.
+AC_CACHE_CHECK([for BTI support], [libc_cv_aarch64_bti], [dnl
+  cat > conftest.c <<EOF
+void foo (void) { }
+EOF
+  libc_cv_aarch64_bti=no
+  if AC_TRY_COMMAND([${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS -nostdlib -nostartfiles $no_ssp -shared -fPIC -o conftest.so conftest.c]) \
+     && AC_TRY_COMMAND([$READELF -lW conftest.so | grep -q GNU_PROPERTY]) \
+     && AC_TRY_COMMAND([$READELF -nW conftest.so | grep -q "NT_GNU_PROPERTY_TYPE_0.*AArch64 feature:.* BTI"])
+  then
+    libc_cv_aarch64_bti=yes
+  fi
+  rm -rf conftest.*])
+if test $libc_cv_aarch64_bti = yes; then
+  AC_DEFINE(HAVE_AARCH64_BTI)
+fi