[PATCH v3 1/4] aarch64: add configure checks for BTI support

[Adhemerval Zanella Netto]

Maybe extend the commit message a bit, with some rationale why this patch is
needed and why you need to check both the compiler, linker, and the GNU
property support.

The patch looks ok, thanks.

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

On 26/11/25 13:45, Yury Khrustalev wrote:
> ---
>  sysdeps/aarch64/configure    | 144 +++++++++++++++++++++++++++++++++++
>  sysdeps/aarch64/configure.ac |  36 +++++++++
>  2 files changed, 180 insertions(+)
> 
> diff --git a/sysdeps/aarch64/configure b/sysdeps/aarch64/configure
> index eecdd324b2..44b833ea1d 100755
> --- a/sysdeps/aarch64/configure
> +++ b/sysdeps/aarch64/configure
> @@ -196,6 +196,150 @@ fi
>  
>  libc_cv_support_sframe=yes
>  
> +# Check if compilers support BTI in branch protection:
> +
> +{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking if compiler supports -mbranch-protection=bti" >&5
> +printf %s "checking if compiler supports -mbranch-protection=bti... " >&6; }
> +if test ${libc_cv_cc_bti+y}
> +then :
> +  printf %s "(cached) " >&6
> +else case e in #(
> +  e) if { ac_try='${CC-cc} -Werror -mbranch-protection=bti -xc /dev/null -S -o /dev/null'
> +  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
> +  (eval $ac_try) 2>&5
> +  ac_status=$?
> +  printf "%s\n" "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
> +  test $ac_status = 0; }; }
> +then :
> +  libc_cv_cc_bti=yes
> +else case e in #(
> +  e) libc_cv_cc_bti=no ;;
> +esac
> +fi ;;
> +esac
> +fi
> +{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: $libc_cv_cc_bti" >&5
> +printf "%s\n" "$libc_cv_cc_bti" >&6; }
> +if test "$TEST_CC" = "$CC"; then
> +  libc_cv_test_cc_bti=$libc_cv_cc_bti
> +else
> +
> +saved_CC="$CC"
> +CC="$TEST_CC"
> +{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking if compiler supports -mbranch-protection=bti in testing" >&5
> +printf %s "checking if compiler supports -mbranch-protection=bti in testing... " >&6; }
> +if test ${libc_cv_test_cc_bti+y}
> +then :
> +  printf %s "(cached) " >&6
> +else case e in #(
> +  e) if { ac_try='${CC-cc} -Werror -mbranch-protection=bti -xc /dev/null -S -o /dev/null'
> +  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
> +  (eval $ac_try) 2>&5
> +  ac_status=$?
> +  printf "%s\n" "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
> +  test $ac_status = 0; }; }
> +then :
> +  libc_cv_test_cc_bti=yes
> +else case e in #(
> +  e) libc_cv_test_cc_bti=no
> + ;;
> +esac
> +fi ;;
> +esac
> +fi
> +{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: $libc_cv_test_cc_bti" >&5
> +printf "%s\n" "$libc_cv_test_cc_bti" >&6; }
> +
> +CC="$saved_CC"
> +
> +fi
> +
> +
> +# Check if linker supports BTI marking
> +{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking for linker that supports -z force-bti" >&5
> +printf %s "checking for linker that supports -z force-bti... " >&6; }
> +libc_linker_feature=no
> +cat > conftest.c <<EOF
> +int _start (void) { return 42; }
> +EOF
> +if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp
> +		  -Wl,-z,force-bti -nostdlib -nostartfiles
> +		  -fPIC -shared -o conftest.so conftest.c
> +		  1>&5'
> +  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
> +  (eval $ac_try) 2>&5
> +  ac_status=$?
> +  printf "%s\n" "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
> +  test $ac_status = 0; }; }
> +then
> +  if ${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS $no_ssp -Wl,-z,force-bti -nostdlib \
> +      -nostartfiles -fPIC -shared -o conftest.so conftest.c 2>&1 \
> +      | grep "warning: -z force-bti ignored" > /dev/null 2>&1; then
> +    true
> +  else
> +    libc_linker_feature=yes
> +  fi
> +fi
> +rm -f conftest*
> +if test $libc_linker_feature = yes; then
> +  libc_cv_ld_bti=yes
> +else
> +  libc_cv_ld_bti=no
> +
> +fi
> +{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: $libc_linker_feature" >&5
> +printf "%s\n" "$libc_linker_feature" >&6; }
> +
> +# Check if toolchain is enabled to support BTI
> +{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking if toolchain is enabled to support BTI" >&5
> +printf %s "checking if toolchain is enabled to support BTI... " >&6; }
> +libc_elf_property=no
> +cat > conftest.c <<EOF
> +int foo (void) { return 42; }
> +EOF
> +if { ac_try='${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS
> +		  -fPIC -shared -o conftest.so conftest.c
> +		  1>&5'
> +  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
> +  (eval $ac_try) 2>&5
> +  ac_status=$?
> +  printf "%s\n" "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
> +  test $ac_status = 0; }; }
> +then
> +  if { ac_try='LC_ALL=C $READELF -n --wide conftest.so | grep "AArch64 feature: .*BTI" 1>&5'
> +  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
> +  (eval $ac_try) 2>&5
> +  ac_status=$?
> +  printf "%s\n" "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
> +  test $ac_status = 0; }; }
> +  then
> +    libc_elf_property=yes
> +  else
> +    libc_elf_property=no
> +  fi
> +fi
> +rm -f conftest*
> +if test $libc_elf_property = yes; then
> +  libc_cv_bti_supported=yes
> +else
> +  libc_cv_bti_supported=no
> +
> +fi
> +{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: result: $libc_elf_property" >&5
> +printf "%s\n" "$libc_elf_property" >&6; }
> +
> +if test $libc_cv_cc_bti = yes && \
> +  test $libc_cv_test_cc_bti = yes && \
> +  test $libc_cv_ld_bti = yes && \
> +  test $libc_cv_bti_supported = yes
> +then
> +  config_vars="$config_vars
> +have-test-bti = yes"
> +else
> +  config_vars="$config_vars
> +have-test-bti = no"
> +fi
> +
>  # Check if compilers support GCS in branch protection:
>  
>  { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking if compiler supports -mbranch-protection=gcs" >&5
> diff --git a/sysdeps/aarch64/configure.ac b/sysdeps/aarch64/configure.ac
> index 8b01aa843d..b9981861f6 100644
> --- a/sysdeps/aarch64/configure.ac
> +++ b/sysdeps/aarch64/configure.ac
> @@ -34,6 +34,42 @@ fi
>  
>  libc_cv_support_sframe=yes
>  
> +# Check if compilers support BTI in branch protection:
> +LIBC_TRY_CC_AND_TEST_CC_OPTION(
> +  [if compiler supports -mbranch-protection=bti],
> +  [-Werror -mbranch-protection=bti],
> +  libc_cv_cc_bti,
> +  [libc_cv_cc_bti=yes],
> +  [libc_cv_cc_bti=no],
> +  libc_cv_test_cc_bti,
> +  [libc_cv_test_cc_bti=yes],
> +  [libc_cv_test_cc_bti=no]
> +)
> +
> +# Check if linker supports BTI marking
> +LIBC_LINKER_FEATURE(
> +  [-z force-bti], [-Wl,-z,force-bti],
> +  [libc_cv_ld_bti=yes], [libc_cv_ld_bti=no]
> +)
> +
> +# Check if toolchain is enabled to support BTI
> +LIBC_CHECK_ELF_PROPERTY(
> +  [if toolchain is enabled to support BTI],
> +  [AArch64 feature: .*BTI],
> +  [libc_cv_bti_supported=yes],
> +  [libc_cv_bti_supported=no]
> +)
> +
> +if test $libc_cv_cc_bti = yes && \
> +  test $libc_cv_test_cc_bti = yes && \
> +  test $libc_cv_ld_bti = yes && \
> +  test $libc_cv_bti_supported = yes
> +then
> +  LIBC_CONFIG_VAR([have-test-bti], [yes])
> +else
> +  LIBC_CONFIG_VAR([have-test-bti], [no])
> +fi
> +
>  # Check if compilers support GCS in branch protection:
>  LIBC_TRY_CC_AND_TEST_CC_OPTION(
>    [if compiler supports -mbranch-protection=gcs],