Re: [PATCH v2] meson: move -no-pie from linker to compiler

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

On 23/5/23 09:30, Paolo Bonzini wrote:
> The large comment in the patch says it all; the -no-pie flag is broken and
> this is why it was not included in QEMU_LDFLAGS before commit a988b4c5614
> ("build: move remaining compiler flag tests to meson", 2023-05-18).  And
> some distros made things even worse, so we have to add it to the compiler
> command line.
> 
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1664
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>   meson.build | 19 ++++++++++++++-----
>   1 file changed, 14 insertions(+), 5 deletions(-)
> 
> diff --git a/meson.build b/meson.build
> index 0a5cdefd4d3d..20accae99281 100644
> --- a/meson.build
> +++ b/meson.build
> @@ -265,12 +265,21 @@ endif
>   
>   # Meson currently only handles pie as a boolean for now, so if the user
>   # has explicitly disabled PIE we need to extend our cflags.
> +#
> +# -no-pie is supposedly a linker flag that has no effect on the compiler
> +# command line, but some distros, that didn't quite know what they were
> +# doing, made local changes to gcc's specs file that turned it into
> +# a compiler command-line flag.
> +#
> +# What about linker flags?  For a static build, no PIE is implied by -static
> +# which we added above (and if it's not because of the same specs patching,
> +# there's nothing we can do: compilation will fail, report a bug to your
> +# distro and do not use --disable-pie in the meanwhile).  For dynamic linking,
> +# instead, we can't add -no-pie because it overrides -shared: the linker then
> +# tries to build an executable instead of a shared library and fails.  So
> +# don't add -no-pie anywhere and cross fingers. :(
>   if not get_option('b_pie')
> -  qemu_common_flags += cc.get_supported_arguments('-fno-pie')
> -  if not get_option('prefer_static')
> -    # No PIE is implied by -static which we added above.
> -    qemu_ldflags += cc.get_supported_link_arguments('-no-pie')
> -  endif
> +  qemu_common_flags += cc.get_supported_arguments('-fno-pie', '-no-pie')
>   endif

This removes this annoying warning with Clang on Darwin/Aarch64:

clang: warning: argument unused during compilation: '-no-pie' 
[-Wunused-command-line-argument]

Tested-by: Philippe Mathieu-Daudé <philmd@linaro.org>