[PATCH v6 09/14] aarch64: ensure objects are BTI compatible

[Adhemerval Zanella]

On 01/07/2020 11:39, Szabolcs Nagy wrote:
> 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.

Is the outlined atomic present in any current released gcc? If so
should we add a configure handler to add -mno-outline-atomics for
such cases?

Besides that LGTM, thanks.

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

> ---
>  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

Ok.

> 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
> 

Ok.