Re: [PATCH] meson: remove -no-pie linker flag

[Daniel P . Berrangé]

On Mon, May 22, 2023 at 10:08:16AM +0200, 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).
> 
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1664
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  meson.build | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/meson.build b/meson.build
> index 0a5cdefd4d3d..6733b2917081 100644
> --- a/meson.build
> +++ b/meson.build
> @@ -267,10 +267,15 @@ endif
>  # has explicitly disabled PIE we need to extend our cflags.
>  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
> +  # What about linker flags?  For a static build, no PIE is implied by 
> -static
> +  # which we added above.  For dynamic linking, adding -no-pie is messy 
> because
> +  # it overrides -shared: the linker then wants to build an executable 
> instead
> +  # of a shared library and the build fails.  Before moving this code to 
> Meson,
> +  # we went through a dozen different commits affecting the usage of -no-pie,
> +  # ultimately settling for a completely broken one that added -no-pie to the
> +  # compiler flags together with -fno-pie... except that -no-pie is a linker
> +  # flag that has no effect on the compiler command line.  So, don't add
> +  # -no-pie anywhere and cross fingers.
>  endif

I'm curious why we need to do anything ?  I would have thought that meson
should handle 'b_pie' itself, passing the right args to $CC that it feels
are appropriate. I don't recall seeing other apps using meson trying to
handle b_pie logic - what's special about QEMU ? IOW, is it possible to
delete this entire b_pie condition and thus avoid worrying about this
problem ?

With regards,
Daniel
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