[dpdk-users] Compiling 32-bit dpdk with meson in 64-bit container

[Renata Saiakhova]

Hi Bruce,

thanks, the second variant is indeed easy! Is there any advantage to create a cross-file instead of just passing an option to compiler and linker and specifying pkg-config libdir? or would it be more "canonical"?

Kind regards,
Renata
________________________________
From: Bruce Richardson <bruce.richardson at intel.com>
Sent: Tuesday, October 13, 2020 6:04 PM
To: Renata Saiakhova <renata.saiakhova at ekinops.com>
Cc: users at dpdk.org <users at dpdk.org>
Subject: Re: Compiling 32-bit dpdk with meson in 64-bit container

On Tue, Oct 13, 2020 at 03:54:13PM +0000, Renata Saiakhova wrote:
>    Hi all, hi Bruce,
>
>    I have an issue to compile 32 bit dpdk (version 20.08) with meson in a
>    64-bit container.
>
>    As I can see from meson.build, it deducts the arch from the cc sizeof:
>
>    dpdk_conf.set('RTE_ARCH_64', cc.sizeof('void *') == 8)
>
>    The attempts to workaround it and set RTE_ARCH_64 to false gives good
>    values in build/rte_build_config.h:
>
>    #define RTE_ARCH i686
>    #undef RTE_ARCH_64
>    #define RTE_ARCH_I686 1
>    #define RTE_ARCH_X86 1
>    #define RTE_CACHE_LINE_SIZE 64
>    but, nevertheless, dpdk is compiled for 64 bit and not for 32 bit.
>    Before, with make build system, RTE_ARCH_ values defined arch and
>    compilation flags for x86 (like -m32 for i686), but with meson it seems
>    to be more complicated?
>    Is there a way to compile 32 bit dpdk (version 20.08) with meson in a
>    64-bit environment?
>    Kind regards,
>    Renata

Hi Renata,

there are two ways to do this - firstly one can create and use a
cross-file, but secondly, and easier, one just needs to tell the compiler
to create 32-bit binaries using the -m32 flag. In this second case, the
only additional complication is that you need to ensure that pkg-config
looks for the relevant .pc files in a 32-bit lib directory rather than a
64-bit one.

Based on that, on my Ubuntu system, the following commands will work to do a
32-bit build of DPDK:

$ PKG_CONFIG_LIBDIR=/usr/lib/i386-linux-gnu/pkgconfig/ meson -Dc_args='-m32' \
        -Dc_link_args='-m32' build-32bit

$ ninja -C build-32bit

Checking the resulting binary:

$ file build-32bit/app/dpdk-testpmd
build-32bit/app/dpdk-testpmd: ELF 32-bit LSB shared object, Intel 80386, \
        version 1 (SYSV), dynamically linked, ...

Depending on your Linux distribution, the pkg-config libdir you need to
specify may be different, e.g. /usr/lib32/pkgconfig, perhaps. Note also
that it's the "_LIBDIR" variable rather than "PKG_CONFIG_PATH" that must
be set, since the latter just appends to the search paths rather than
replacing them with 32-bit versions.

Regards,
/Bruce