From: Szabolcs Nagy <szabolcs.nagy@arm.com>
Date: Tue, 30 Jun 2020 10:12:40 +0000 (+0100)
Subject: aarch64: ensure objects are BTI compatible
X-Git-Tag: glibc-2.32~97
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=de9301c02e898fb20a609b459d81afda42f39c61;p=thirdparty%2Fglibc.git

aarch64: ensure objects are BTI compatible

When glibc is built with branch protection (i.e. with a gcc configured
with --enable-standard-branch-protection), all glibc binaries should
be BTI compatible and marked as such.

It is easy to link BTI incompatible objects by accident and this is
silent currently which is usually not the expectation, so this is
changed into a link error. (There is no linker flag for failing on
BTI incompatible inputs so all warnings are turned into fatal errors
outside the test system when building glibc with branch protection.)

Unfortunately, outlined atomic functions are not BTI compatible in
libgcc (PR libgcc/96001), so to build glibc with current gcc use
'CC=gcc -mno-outline-atomics', this should be fixed in libgcc soon
and then glibc can be built and tested without such workarounds.

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
---

diff --git a/sysdeps/aarch64/Makefile b/sysdeps/aarch64/Makefile
index 5ae8b082b0b..7f82fc055e3 100644
--- a/sysdeps/aarch64/Makefile
+++ b/sysdeps/aarch64/Makefile
@@ -1,5 +1,13 @@
 long-double-fcts = yes
 
+ifeq (yes,$(aarch64-bti))
+# Mark linker output BTI compatible, it warns on non-BTI inputs.
+sysdep-LDFLAGS += -Wl,-z,force-bti
+# Make warnings fatal outside the test system.
+LDFLAGS-lib.so += -Wl,--fatal-warnings
+LDFLAGS-rtld += -Wl,-z,force-bti,--fatal-warnings
+endif
+
 ifeq ($(subdir),elf)
 sysdep-dl-routines += dl-bti
 endif
diff --git a/sysdeps/aarch64/configure b/sysdeps/aarch64/configure
index 70477a7fa56..c6375404364 100644
--- a/sysdeps/aarch64/configure
+++ b/sysdeps/aarch64/configure
@@ -210,6 +210,8 @@ EOF
 fi
 { $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_aarch64_bti" >&5
 $as_echo "$libc_cv_aarch64_bti" >&6; }
+config_vars="$config_vars
+aarch64-bti = $libc_cv_aarch64_bti"
 if test $libc_cv_aarch64_bti = yes; then
   $as_echo "#define HAVE_AARCH64_BTI 1" >>confdefs.h
 
diff --git a/sysdeps/aarch64/configure.ac b/sysdeps/aarch64/configure.ac
index 798f4947400..2c2817514d7 100644
--- a/sysdeps/aarch64/configure.ac
+++ b/sysdeps/aarch64/configure.ac
@@ -36,6 +36,7 @@ EOF
     libc_cv_aarch64_bti=yes
   fi
   rm -rf conftest.*])
+LIBC_CONFIG_VAR([aarch64-bti], [$libc_cv_aarch64_bti])
 if test $libc_cv_aarch64_bti = yes; then
   AC_DEFINE(HAVE_AARCH64_BTI)
 fi