[PATCH v2 3/6] configure: Repurpose have-cc-with-libunwind for clang support

[Sam James]

Adhemerval Zanella <adhemerval.zanella@linaro.org> writes:

> The `have-cc-with-libunwind` check (and its corresponding macro
> HAVE_CC_WITH_LIBUNWIND) was historically specific to IA64, intended
> to supplement libgcc with libunwind.  Since this logic is unused in
> current GCC configurations, this patch repurposes it to support
> clang-based toolchains that utilize LLVM's libunwind instead of
> libgcc_s.
>
> The configure script now detects if the compiler natively supports
> unwinding via `-lunwind`.

I was going to comment about this then checked the next patch :)

>
> Additionally, when this mode is enabled, `-lclang_rt.builtins` is
> explicitly added to the `libgcc_eh` definition.  This is necessary
> because `links-dso-program` otherwise fails to link due to a missing
> `__gcc_personality_v0` symbol.  It appears that clang does not
> automatically link the builtins providing this personality routine
> when `rlink-path` is actively used during the build.

Yes, we've ran into this before.

LGTM, thanks.

Reviewed-by: Sam James <sam@gentoo.org>

> ---
>  Makeconfig       |  6 ++++--
>  Makerules        |  3 ++-
>  config.make.in   |  1 -
>  configure        | 11 ++++++-----
>  configure.ac     |  9 +++++----
>  support/Makefile |  2 +-
>  6 files changed, 18 insertions(+), 14 deletions(-)
>
> diff --git a/Makeconfig b/Makeconfig
> index 6a05e1d973..ea509dd3bc 100644
> --- a/Makeconfig
> +++ b/Makeconfig
> @@ -711,10 +711,12 @@ link-libc-static-tests = -Wl,--start-group $(common-objpfx)libc.a $(static-gnuli
>  ifndef gnulib
>  ifneq ($(have-cc-with-libunwind),yes)
>    libunwind =
> +  libgcc_s  = -lgcc_s
>  else
> -  libunwind = -lunwind
> +  libunwind = -lunwind $(libgcc-name)
> +  libgcc_s = $(libunwind)
>  endif
> -libgcc_eh := -Wl,--as-needed -lgcc_s $(libunwind) -Wl,--no-as-needed
> +libgcc_eh := -Wl,--as-needed $(libgcc_s) -Wl,--no-as-needed
>  gnulib-arch =
>  gnulib = $(libgcc-name) $(gnulib-arch)
>  gnulib-tests := $(libgcc-name) $(libgcc_eh)
> diff --git a/Makerules b/Makerules
> index 30c3559a28..180cbee251 100644
> --- a/Makerules
> +++ b/Makerules
> @@ -565,7 +565,8 @@ $(LINK.o) -shared -static-libgcc $(sysdep-LDFLAGS) $(rtld-LDFLAGS) \
>  	  -B$(csu-objpfx) $(load-map-file) \
>  	  $(LDFLAGS.so) $(LDFLAGS-$(@F:%.so=%).so) \
>  	  $(link-test-modules-rpath-link) \
> -	  -L$(subst :, -L,$(rpath-link)) -Wl,-rpath-link=$(rpath-link)
> +	  -L$(subst :, -L,$(rpath-link)) -Wl,-rpath-link=$(rpath-link) \
> +	  $(libgcc_eh)
>  endef
>  
>  # This macro is similar to build-shlib but it does not define a soname
> diff --git a/config.make.in b/config.make.in
> index fca75ab5d3..42889716e4 100644
> --- a/config.make.in
> +++ b/config.make.in
> @@ -69,7 +69,6 @@ no-fortify-source = @no_fortify_source@
>  have-selinux = @have_selinux@
>  have-libaudit = @have_libaudit@
>  have-libcap = @have_libcap@
> -have-cc-with-libunwind = @libc_cv_cc_with_libunwind@
>  bind-now = @bindnow@
>  have-cxx-thread_local = @libc_cv_cxx_thread_local@
>  have-loop-to-function = @libc_cv_cc_loop_to_function@
> diff --git a/configure b/configure
> index 672b1abad8..d156912063 100755
> --- a/configure
> +++ b/configure
> @@ -7069,18 +7069,17 @@ if test $libc_cv_have_sdata_section = yes; then
>  
>  fi
>  
> -{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking for libunwind-support in compiler" >&5
> -printf %s "checking for libunwind-support in compiler... " >&6; }
> +{ printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether the compiler links with libunwind" >&5
> +printf %s "checking whether the compiler links with libunwind... " >&6; }
>  if test ${libc_cv_cc_with_libunwind+y}
>  then :
>    printf %s "(cached) " >&6
>  else case e in #(
> -  e)
> -  cat > conftest.c <<EOF
> +  e) cat > conftest.c <<EOF
>  int main (void) { return 0; }
>  EOF
>    if ${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS -static -o conftest \
> -     conftest.c -v 2>&1 >/dev/null | grep ' -lunwind ' >/dev/null; then
> +     conftest.c -v 2>&1 >/dev/null | grep 'libunwind.a' >/dev/null; then
>      libc_cv_cc_with_libunwind=yes
>    else
>      libc_cv_cc_with_libunwind=no
> @@ -7095,6 +7094,8 @@ if test $libc_cv_cc_with_libunwind = yes; then
>    printf "%s\n" "#define HAVE_CC_WITH_LIBUNWIND 1" >>confdefs.h
>  
>  fi
> +config_vars="$config_vars
> +have-cc-with-libunwind = $libc_cv_cc_with_libunwind"
>  
>  ASFLAGS_config=
>  { printf "%s\n" "$as_me:${as_lineno-$LINENO}: checking whether --noexecstack is desirable for .S files" >&5
> diff --git a/configure.ac b/configure.ac
> index aa50f28e60..776695486a 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -1289,13 +1289,13 @@ if test $libc_cv_have_sdata_section = yes; then
>    AC_DEFINE(HAVE_SDATA_SECTION)
>  fi
>  
> -AC_CACHE_CHECK(for libunwind-support in compiler,
> -	       libc_cv_cc_with_libunwind, [
> -  cat > conftest.c <<EOF
> +AC_CACHE_CHECK(whether the compiler links with libunwind,
> +	       libc_cv_cc_with_libunwind, [dnl
> +cat > conftest.c <<EOF
>  int main (void) { return 0; }
>  EOF
>    if ${CC-cc} $CFLAGS $CPPFLAGS $LDFLAGS -static -o conftest \
> -     conftest.c -v 2>&1 >/dev/null | grep ' -lunwind ' >/dev/null; then
> +     conftest.c -v 2>&1 >/dev/null | grep 'libunwind.a' >/dev/null; then
>      libc_cv_cc_with_libunwind=yes
>    else
>      libc_cv_cc_with_libunwind=no
> @@ -1305,6 +1305,7 @@ AC_SUBST(libc_cv_cc_with_libunwind)
>  if test $libc_cv_cc_with_libunwind = yes; then
>    AC_DEFINE(HAVE_CC_WITH_LIBUNWIND)
>  fi
> +LIBC_CONFIG_VAR([have-cc-with-libunwind], [$libc_cv_cc_with_libunwind])
>  
>  ASFLAGS_config=
>  AC_CACHE_CHECK(whether --noexecstack is desirable for .S files,
> diff --git a/support/Makefile b/support/Makefile
> index b83350180c..1dae2802cf 100644
> --- a/support/Makefile
> +++ b/support/Makefile
> @@ -319,7 +319,7 @@ LINKS_DSO_PROGRAM = links-dso-program-c
>  LDLIBS-links-dso-program-c = $(gnulib)
>  ifeq ($(have-libgcc_s),yes)
>  CFLAGS-links-dso-program-c.c += -fexceptions
> -LDLIBS-links-dso-program-c += -lgcc_s $(libunwind)
> +LDLIBS-links-dso-program-c += $(libgcc_s) $(libunwind)
>  endif
>  else
>  LINKS_DSO_PROGRAM = links-dso-program
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