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

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

[Paolo Bonzini]

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
 
 if not get_option('stack_protector').disabled()
-- 
2.40.1

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

[Philippe Mathieu-Daudé]

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>

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

[Richard Henderson]

On 5/23/23 00:30, 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(-)

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Tested-by: Richard Henderson <richard.henderson@linaro.org>


r~

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

[Volker Rümelin]

Am 23.05.23 um 09:30 schrieb Paolo Bonzini:
> 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
>   
>   if not get_option('stack_protector').disabled()

I tested that QEMU builds on Windows with MSYS2 mingw64.

One unrelated note: The DLL loader doesn't find the libslirp-0.dll when 
QEMU was built with libslirp from the subprojects folder and started 
from the build folder. It's necessary to copy this library to a folder 
in the DLL search path.

Tested-by: Volker Rümelin <vr_qemu@t-online.de>