[glibc/vineet/arc-port-latest] aarch64: ensure objects are BTI compatible

[glibc/vineet/arc-port-latest] aarch64: ensure objects are BTI compatible

[Vineet Gupta]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=de9301c02e898fb20a609b459d81afda42f39c61

commit de9301c02e898fb20a609b459d81afda42f39c61
Author: Szabolcs Nagy <szabolcs.nagy@arm.com>
Date:   Tue Jun 30 11:12:40 2020 +0100

    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:
---
 sysdeps/aarch64/Makefile     | 8 ++++++++
 sysdeps/aarch64/configure    | 2 ++
 sysdeps/aarch64/configure.ac | 1 +
 3 files changed, 11 insertions(+)

diff --git a/sysdeps/aarch64/Makefile b/sysdeps/aarch64/Makefile
index 5ae8b082b0..7f82fc055e 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 70477a7fa5..c637540436 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 798f494740..2c2817514d 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