[dpdk-dev] [dpdk-stable] [PATCH 2/2] eal: fix loading of shared libs from driver plugin directories

[David Marchand]

On Tue, Nov 24, 2020 at 4:15 PM Timothy Redaelli <tredaelli at redhat.com> wrote:
>
> Commit 49b536fc3060 ("eal: load only shared libs from driver plugin directories")
> introduced a check that any shared library must ends with .so, but it can't
> work, at least, on Fedora/CentOS/RHEL since .so symlinks are not installed
> when you install dpdk package, but only when you install dpdk-devel package.
>
> This commit adds also a check for .so.ABI_VERSION to check for shared
> lib.
>
> See Fedora Packaging Guidelines for more informations:
> https://docs.fedoraproject.org/en-US/packaging-guidelines/#_devel_packages
>
> Fixes: 49b536fc3060 ("eal: load only shared libs from driver plugin directories")
> Cc: bruce.richardson at intel.com
> Signed-off-by: Timothy Redaelli <tredaelli at redhat.com>
> ---
>  lib/librte_eal/common/eal_common_options.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/lib/librte_eal/common/eal_common_options.c b/lib/librte_eal/common/eal_common_options.c
> index e6f77ad217..e9e2362c53 100644
> --- a/lib/librte_eal/common/eal_common_options.c
> +++ b/lib/librte_eal/common/eal_common_options.c
> @@ -402,8 +402,10 @@ eal_plugindir_init(const char *path)
>                 struct stat sb;
>                 int nlen = strnlen(dent->d_name, sizeof(dent->d_name));
>
> -               /* check if name ends in .so */
> -               if (strcmp(&dent->d_name[nlen - 3], ".so") != 0)
> +               /* check if name ends in .so or .so.ABI_VERSION */
> +               if (strcmp(&dent->d_name[nlen - 3], ".so") != 0 &&
> +                   strcmp(&dent->d_name[nlen - 4 - strlen(ABI_VERSION)],
> +                          ".so."ABI_VERSION) != 0)
>                         continue;
>
>                 snprintf(sopath, sizeof(sopath), "%s/%s", path, dent->d_name);

A first doubt I had about this patch is about multiple loading of the
same driver, and its effects.
So I first had a look at the main branch current state (using
devtools/test-null.sh) and I can see multiple loading already happens
for statically linked drivers like the bond driver.

$ LD_LIBRARY_PATH=build/lib gdb build/app/dpdk-testpmd -ex "b main"
-ex "run -c 3 --no-huge -m 20 -d build/drivers '--log-level=*:debug'
-a 0:0.0 --vdev net_null1 --vdev net_null2 -- --no-mlockall
--total-num-mbufs=2048 -ia"
...
(gdb) info sharedlibrary
...
0x00007ffff796d5b0  0x00007ffff797d2d6  Yes
/home/dmarchan/dpdk/build/app/../drivers/librte_net_bond.so.21
...
(gdb) b rte_eal_init
(gdb) c
(gdb) finish
...
EAL: open shared lib build/drivers/librte_net_avp.so
EAL: open shared lib build/drivers/librte_net_bond.so
EAL: open shared lib build/drivers/librte_net_ixgbe.so
...
(gdb) set $elm=*(struct shared_driver *)solib_list.tqh_first
(gdb) while $elm
p $elm
set $elm=*(struct shared_driver *)($elm.next.tqe_next)
end
...
$67 = {next = {tqe_next = 0x5c3350, tqe_prev = 0x5c1310}, name =
"build/drivers/librte_net_avp.so", '\000' <repeats 4064 times>,
lib_handle = 0x616870}
$68 = {next = {tqe_next = 0x5c4370, tqe_prev = 0x5c2330}, name =
"build/drivers/librte_net_bond.so", '\000' <repeats 4063 times>,
lib_handle = 0x7ffff7995a80}
$69 = {next = {tqe_next = 0x5c5390, tqe_prev = 0x5c3350}, name =
"build/drivers/librte_net_ixgbe.so", '\000' <repeats 4062 times>,
lib_handle = 0x7ffff7942fc0}
...

I could not confirm the 0x7ffff7995a80 handle points at the first load
of the bond driver.
gdb does not seem to know of the linker internal structures, a bit
hard to tell but the addresses are in the same range, so likely the
same object.

I confirmed the bond constructor only being called once when the bond
driver is loaded because of static link:

$ LD_LIBRARY_PATH=build/lib gdb build/app/dpdk-testpmd -ex "b
vdrvinitfn_pmd_bond_drv" -ex "run -c 3 --no-huge -m 20 -d
build/drivers '--log-level=*:debug' -a 0:0.0 --vdev net_null1 --vdev
net_null2 -- --no-mlockall --total-num-mbufs=2048 -ia"
GNU gdb (GDB) Fedora 8.3.50.20190824-30.fc31
...
Reading symbols from build/app/dpdk-testpmd...
Function "vdrvinitfn_pmd_bond_drv" not defined.
Make breakpoint pending on future shared library load? (y or [n]) y
Breakpoint 1 (vdrvinitfn_pmd_bond_drv) pending.
Starting program: /home/dmarchan/dpdk/build/app/dpdk-testpmd -c 3
--no-huge -m 20 -d build/drivers '--log-level=*:debug' -a 0:0.0 --vdev
net_null1 --vdev net_null2 -- --no-mlockall --total-num-mbufs=2048 -ia
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/usr/lib64/libthread_db.so.1".

Breakpoint 1, vdrvinitfn_pmd_bond_drv () at
../drivers/net/bonding/rte_eth_bond_pmd.c:3755
3755    RTE_PMD_REGISTER_VDEV(net_bonding, pmd_bond_drv);
Missing separate debuginfos, use: dnf debuginfo-install
elfutils-libelf-0.179-2.fc31.x86_64 glibc-2.30-13.fc31.x86_64
jansson-2.12-4.fc31.x86_64 libbsd-0.9.1-4.fc31.x86_64
libfdt-1.6.0-1.fc31.x86_64 numactl-libs-2.0.12-3.fc31.x86_64
zlib-1.2.11-20.fc31.x86_64

(gdb) c
Continuing.
...
EAL: open shared lib build/drivers/librte_net_avp.so
EAL: open shared lib build/drivers/librte_net_bond.so
EAL: open shared lib build/drivers/librte_net_ixgbe.so
...
testpmd>


Now, about this patch.
In this test, it has the effect of loading all drivers twice (or
thrice if statically linked).
I see no problem with it since the linker is intelligent enough and
constructors are only called once.


My only remaining doubt is whether we should be looking for
.ABI_VERSION or .ABI_MAJOR extension.
This could be discussed, but in its current form, this patch lgtm.

Acked-by: David Marchand <david.marchand at redhat.com>


-- 
David Marchand