Re: [Buildroot] [PATCH] package/qemu: force the host compiler to look at HOST_DIR first

["Yann E. MORIN" <yann.morin.1998@free.fr>]

Romain, All,

+Bernd for the meson bump

On 2023-08-19 01:46 +0200, Romain Naour spake thusly:
> Since meson 1.2.0, compiler's search path are retrieved and used
> to link a library. If the same library is installed on the host
> and build by Buildroot (HOST_DIR/lib), meson now link against
> the one found in the compiler's search path instead of linking
> agains the one provided by Buildroot.
> 
> See: https://github.com/mesonbuild/meson/issues/11914#issuecomment-1678090566
> 
> Help the compiler by setting -Bprefix that specifies a path where to find the
> executables, libraries, include files, and data files of the compiler itself.
> For each subprogram to be run, the compiler driver first tries the -B prefix,
> if any. If that name is not found, or if -B is not specified, the driver
> tries two standard prefixes, /usr/lib/gcc/ and /usr/local/lib/gcc/.

So, I understand that this makes qemu actually build, but I am afraid
this is just hidign the problem.

Indeed, it is possible that we have other host packages that depend on
some of the host libs we build and that may exist on the system, and
those packages are also going to break.

For example, host-efl is a host-meson-package, and depends on
host-libglib2, so presumably we would hav e the issue there too.

We can't fix the breakage by adding -B to all the host packages one by
one. If -B is idneed the correct fix (I doubt it), then we will have to
add it to the common HOST_CFLAGS, HOST_CXXFLAGS and so on...

However, what bothers me slighhtly, is why the qemu link step uses two
different ways to link with the libglib2 libraries, e.g.:

    -l/path/to/host/lib/libgio-2.0.so
    -L/path/to/host/lib -lgmodule-2.0

So, why is libgio handled with an absolute path, while libgmodule is
not? Note that libgio does have a DT_NEEDED on libgmodule.

However, let's have a look at the pkg-config files, let's start with
gio-2.0.pc:

    Requires: glib-2.0, gobject-2.0
    Requires.private: gmodule-no-export-2.0, zlib, mount >= 2.23
    Libs: -L${libdir} -lgio-2.0
    Libs.private: -ldl -lresolv

OK, then gmodule-no-export-2.0.pc:

    Requires: glib-2.0
    Libs: -L${libdir} -lgmodule-2.0 -pthread
    Libs.private: -ldl

So, the two are similar. I am not sure to understand how we end up in
this situation, though... :-/

In the meantime, since the bump to meson 1.2.0 is causing the issue with
out an easy fix in sight, I'll revert the meson bump.

Regards,
Yann E. MORIN.

> Fixes:
>     host/lib/libgio-2.0.so: undefined reference to `g_module_open_full'
>     collect2: error: ld returned 1 exit statu
> 
> The problem only appear if we have two version of the glib2 library installed
> on the system:
> 
> [Buildroot]/host/lib/libgio-2.0.so.0.7600.1
> /usr/lib/x86_64-linux-gnu/libgio-2.0.so.0.6600.8
> 
> This is probably a meson bug introduced by [1] since the error message is wrong!
> 
> $ strings output/host/lib/libgio-2.0.so | grep g_module_open_full
> g_module_open_full
> 
> The libgio-2.0.so provided by Buildroot contains the g_module_open_full symbol
> while the libgio-2.0.so installed on the host is too old to have it:
> 
> $ strings /usr/lib/x86_64-linux-gnu/libgio-2.0.so.0.6600.8 | grep g_module_open_full
> 
> [1] https://github.com/mesonbuild/meson/commit/59cfbf68e00aa774a9868101f423bd662938c15d
> 
> Signed-off-by: Romain Naour <romain.naour@gmail.com>
> Cc: Nicolas CARRIER <carrier.nicolas0@gmail.com>
> ---
> This meson issue may be not specific to host-qemu...
> ---
>  package/qemu/qemu.mk | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/package/qemu/qemu.mk b/package/qemu/qemu.mk
> index b341d0220d..8a8dddee58 100644
> --- a/package/qemu/qemu.mk
> +++ b/package/qemu/qemu.mk
> @@ -401,7 +401,18 @@ HOST_QEMU_ARCH = sh4eb
>  endif
>  HOST_QEMU_SYS_ARCH ?= $(HOST_QEMU_ARCH)
>  
> -HOST_QEMU_CFLAGS = $(HOST_CFLAGS)
> +# Since meson 1.2.0, compiler's search path are retrieved and used
> +# to link a library. If the same library is installed on the host
> +# and build by Buildroot (HOST_DIR/lib), meson now link against
> +# the one found in the compiler's search path instead of linking
> +# agains the one provided by Buildroot.
> +# https://github.com/mesonbuild/meson/issues/11914#issuecomment-1678090566
> +# Help the compiler by setting -Bprefix that specifies where to find the
> +# executables, libraries, include files, and data files of the compiler itself.
> +# For each subprogram to be run, the compiler driver first tries the -B prefix,
> +# if any. If that name is not found, or if -B is not specified, the driver
> +# tries two standard prefixes, /usr/lib/gcc/ and /usr/local/lib/gcc/.
> +HOST_QEMU_CFLAGS = $(HOST_CFLAGS) -B$(HOST_DIR)/lib
>  
>  ifeq ($(BR2_PACKAGE_HOST_QEMU_SYSTEM_MODE),y)
>  HOST_QEMU_TARGETS += $(HOST_QEMU_SYS_ARCH)-softmmu
> -- 
> 2.41.0
> 
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