From: Vitaly Chikunov <vt@altlinux.org>
To: Ihor Solodrai <ihor.solodrai@linux.dev>
Cc: bot+bpf-ci@kernel.org, ast@kernel.org, andrii@kernel.org,
daniel@iogearbox.net, eddyz87@gmail.com, olsajiri@gmail.com,
yatsenko@meta.com, alexis.lothore@bootlin.com,
ameryhung@gmail.com, bpf@vger.kernel.org,
linux-kernel@vger.kernel.org, kernel-team@meta.com,
martin.lau@kernel.org, yonghong.song@linux.dev, clm@meta.com
Subject: Re: [PATCH bpf v3 01/15] selftests/bpf: Pass through build flags to bpftool and resolve_btfids
Date: Tue, 3 Mar 2026 07:01:00 +0300 [thread overview]
Message-ID: <aaZOdWs7OS8Pn1Pl@altlinux.org> (raw)
In-Reply-To: <de42bb10-dafd-45da-97fe-b59be487f30b@linux.dev>
Ihor,
On Mon, Mar 02, 2026 at 02:42:11PM -0800, Ihor Solodrai wrote:
> On 3/2/26 12:27 PM, Vitaly Chikunov wrote:
> > On Mon, Mar 02, 2026 at 10:01:59AM -0800, Ihor Solodrai wrote:
> >> On 3/2/26 7:22 AM, Vitaly Chikunov wrote:
> >>> On Fri, Feb 20, 2026 at 08:23:51PM -0800, Ihor Solodrai wrote:
> >>>> On 2/20/26 2:57 PM, bot+bpf-ci@kernel.org wrote:
> >>>>>> diff --git a/tools/bpf/resolve_btfids/Makefile b/tools/bpf/resolve_btfids/Makefile
> >>>>>> index 1733a6e93a07..ef083602b73a 100644
> >>>>>> --- a/tools/bpf/resolve_btfids/Makefile
> >>>>>> +++ b/tools/bpf/resolve_btfids/Makefile
> >>>>>> @@ -65,6 +65,9 @@ $(BPFOBJ): $(wildcard $(LIBBPF_SRC)/*.[ch] $(LIBBPF_SRC)/Makefile) | $(LIBBPF_OU
> >>>>>> LIBELF_FLAGS := $(shell $(HOSTPKG_CONFIG) libelf --cflags 2>/dev/null)
> >>>>>> LIBELF_LIBS := $(shell $(HOSTPKG_CONFIG) libelf --libs 2>/dev/null || echo -lelf)
> >>>>>>
> >>>>>> +ZLIB_LIBS := $(shell $(HOSTPKG_CONFIG) zlib --libs 2>/dev/null || echo -lz)
> >>>>>> +ZSTD_LIBS := $(shell $(HOSTPKG_CONFIG) libzstd --libs 2>/dev/null || echo -lzstd)
> >>>>>
> >>>>> The "|| echo -lzstd" fallback makes zstd an unconditional link
> >>>>> dependency. On systems where libzstd-dev is not installed, pkg-config
> >>>>> fails and the fallback provides -lzstd, but the linker cannot find the
> >>>>> library and the build fails.
> >>>>>
> >>>>> bpftool handles the same transitive dependency conditionally via a
> >>>>> feature test:
> >>>>>
> >>>>> tools/bpf/bpftool/Makefile:
> >>>>> ifeq ($(feature-libelf-zstd),1)
> >>>>> LIBS += -lzstd
> >>>>> LIBS_BOOTSTRAP += -lzstd
> >>>>> endif
> >>>>>
> >>>>> Would it be safer to drop the fallback here so ZSTD_LIBS is empty
> >>>>> when zstd is not available?
> >>>>>
> >>>>> ZSTD_LIBS := $(shell $(HOSTPKG_CONFIG) libzstd --libs 2>/dev/null)
> >>>>>
> >>>>> This would still link zstd when present (needed for the static linking
> >>>>> case where libelf.a pulls in ZSTD symbols from elf_compress.o), but
> >>>>> avoid breaking dynamic builds on systems without libzstd-dev.
> >>>>
> >>>> [...]
> >>>>
> >>>>
> >>>> So, while AI may be technically correct that the build will fail if
> >>>> libelf is installed and libzstd is not, it seems a far-fetched
> >>>> situation, given that libelf depends on libzstd.
> >>>
> >>> This is not far-fetched, and we have build failure for v7.0-rc2 due to
> >>> this.
> >>>
> >>> ld: cannot find -lzstd: No such file or directory
> >>>
> >>> Even though libelf is linked with libzstd, this does not imply
> >>> libzstd-devel (with headers and so library) is there when building.
> >>
> >> Does AI's suggestion make sense in your case then?
> >> That is, make ZSTD_LIBS empty in case pkg-config didn't find libzstd?
> >>
> >> I'm happy to fix this, the build shouldn't fail unless it must.
> >>
> >> But I am curious how and why an environment building Linux with BTF
> >> (requiring build and run of resolve_btfids), which needs libelf-dev
> >> and presumably its dependencies, would exclude/avoid installing
> >> libzstd-dev?
> >
> > Are you providing -lzstd just to link with libelf? I don't think you need to
>
> An explicit -lzstd flag was added to enable a static build [1].
>
> > care about zstd in that case. libelf is already linked with libzstd. If you
> > don't use libzstd functions yourself you don't need to link with -lzstd.
> >
> > Example build without -lzstd:
> >
> > builder@x86_64:~/RPM/BUILD/kernel-image-7.0-rc2$ grep zstd tools/bpf/resolve_btfids/Makefile
> > ZSTD_LIBS := $(shell $(HOSTPKG_CONFIG) libzstd --libs 2>/dev/null)
> >
> > builder@x86_64:~/RPM/BUILD/kernel-image-7.0-rc2$ ldd ./tools/bpf/resolve_btfids/resolve_btfids
> > linux-vdso.so.1 (0x00007ff8b2329000)
> > libelf.so.1 => /lib64/libelf.so.1 (0x00007ff8b2287000)
> > libz.so.1 => /lib64/libz.so.1 (0x00007ff8b2269000)
> > libc.so.6 => /lib64/libc.so.6 (0x00007ff8b206e000)
> > libzstd.so.1 => /lib64/libzstd.so.1 (0x00007ff8b1fc8000)
> > /lib64/ld-linux-x86-64.so.2 (0x00007ff8b232b000)
> > builder@x86_64:~/RPM/BUILD/kernel-image-7.0-rc2$ rpm -q libzstd
> > libzstd-1.5.5-alt2.x86_64
> > builder@x86_64:~/RPM/BUILD/kernel-image-7.0-rc2$ rpm -q libzstd-devel
> > package libzstd-devel is not installed
> >
> > lib*-devel/-dev packages only required if your source is directly using the
> > target lib, in other causes this is already handled.
>
> The issue that AI has raised is whether to leave -lzstd link flag by
> default or not. I decided to leave it on the assumption that the
> environments building Linux with BTF (hence building and running
> resovle_btfids) would have libelf-dev installed (because -lelf has
> been a requirement forever [2]), and libzstd-dev is its dependency.
>
> I checked a few recent distros, all of them have libzstd-dev as a
> direct dependency of libelf-dev, which supports my assumption:
>
> # Fedora
> $ dnf repoquery --providers-of=depends elfutils-libelf-devel
> Updating and loading repositories:
> Repositories loaded.
> elfutils-libelf-0:0.194-1.fc43.i686
> elfutils-libelf-0:0.194-1.fc43.x86_64
> libzstd-devel-0:1.5.7-2.fc43.i686
> libzstd-devel-0:1.5.7-2.fc43.x86_64
Interesting, but looks like this is not needed package dependency.
[fodora:rawhide@docker /]# grep zstd /usr/lib64/pkgconfig/libelf.pc
Requires.private: zlib libzstd
It's only a private dependency not exposed to the application.
pkg-config will not add -lzstd to link with libelf.so. (Unless it's
-static linking.) See pkg-config(1):
Requires.private:
A list of packages required by this package. The difference from Requires is
that the packages listed under Requires.private are not taken into account when
a flag list is computed for dynamically linked executable (i.e., when --static
was not specified). In the situation where each .pc file corresponds to a
library, Requires.private shall be used exclusively to specify the dependencies
between the libraries.
Perhaps, for your static linking case, you just need to extract -static from
EXTRA_LDFLAGS and add it to `pkg-config libelf --libs` to get the list of
static libraries to link with libelf, without defining ZSTD_LIBS at all.
This may provide other important flags besides these, see for example:
alt:sisyphus# pkg-config libelf --libs --static
-lelf -lz -lzstd -pthread
I think it's better to rely on pkg-config instead of guessing all the required
linking flags.
> pkgconf-pkg-config-0:2.3.0-3.fc43.i686
> pkgconf-pkg-config-0:2.3.0-3.fc43.x86_64
> zlib-ng-compat-devel-0:2.3.3-1.fc43.i686
> zlib-ng-compat-devel-0:2.3.3-1.fc43.x86_64
>
> # Ubuntu
> $ apt info libelf-dev
> Package: libelf-dev
> Version: 0.190-1.1ubuntu0.1
> Priority: optional
> Section: libdevel
> Source: elfutils
> Origin: Ubuntu
> Maintainer: Ubuntu Developers <ubuntu-devel-discuss@lists.ubuntu.com>
> Original-Maintainer: Debian Elfutils Maintainers <debian-gcc@lists.debian.org>
> Bugs: https://bugs.launchpad.net/ubuntu/+filebug
> Installed-Size: 385 kB
> Depends: libelf1t64 (= 0.190-1.1ubuntu0.1), zlib1g-dev, libzstd-dev
> Conflicts: libelfg0-dev
> [...]
>
> # Debian
> $ apt info libelf-dev
> Package: libelf-dev
> Version: 0.192-4
> Priority: optional
> Section: libdevel
> Source: elfutils
> Maintainer: Debian Elfutils Maintainers <debian-gcc@lists.debian.org>
> Installed-Size: 420 kB
> Depends: libelf1t64 (= 0.192-4), zlib1g-dev, libzstd-dev
> Conflicts: libelfg0-dev
> [...]
I don't know why these distros do this sort of dependency. In ALT Linux we
don't require libzstd-devel for linelf-devel, also, I just checked OpenMandriva
and it does not require this too. But, openSUSE requires libzstd-devel.
> Of course it's plausible to have a system where libelf-dev is present
> while libzstd-dev is not, as demonstrated by you running one.
>
> Anyways this is easy to fix, I'll send a patch shortly.
Thanks,
>
> [1] https://lore.kernel.org/bpf/4ff82800-2daa-4b9f-95a9-6f512859ee70@linux.dev/
> [2] https://lore.kernel.org/bpf/20200711215329.41165-2-jolsa@kernel.org/
>
>
> >
> > Thanks,
> >
> >>
> >> Thanks.
> >>
> >>>
> >>> Thanks,
> >>>
> >>>>
> >>>> I think we can leave the default -lzstd to have an explicit
> >>>> dependency in the Makefile.
> >>>>
> >>>>
> >>>>>
> >>>>> [ ... ]
> >>
next prev parent reply other threads:[~2026-03-03 4:01 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-02-20 22:25 [PATCH bpf v3 00/15] selftests/bpf: Fixes for userspace ASAN Ihor Solodrai
2026-02-20 22:25 ` [PATCH bpf v3 01/15] selftests/bpf: Pass through build flags to bpftool and resolve_btfids Ihor Solodrai
2026-02-20 22:57 ` bot+bpf-ci
2026-02-21 4:23 ` Ihor Solodrai
2026-03-02 15:22 ` Vitaly Chikunov
2026-03-02 18:01 ` Ihor Solodrai
2026-03-02 20:27 ` Vitaly Chikunov
2026-03-02 22:42 ` Ihor Solodrai
2026-03-03 4:01 ` Vitaly Chikunov [this message]
2026-02-20 22:25 ` [PATCH bpf v3 02/15] resolve_btfids: Fix memory leaks reported by ASAN Ihor Solodrai
2026-02-20 22:25 ` [PATCH bpf v3 03/15] selftests/bpf: Add DENYLIST.asan Ihor Solodrai
2026-02-20 22:25 ` [PATCH bpf v3 04/15] selftests/bpf: Refactor bpf_get_ksyms() trace helper Ihor Solodrai
2026-02-20 22:25 ` [PATCH bpf v3 05/15] selftests/bpf: Fix memory leaks in tests Ihor Solodrai
2026-02-20 22:25 ` [PATCH bpf v3 06/15] selftests/bpf: Fix cleanup in check_fd_array_cnt__fd_array_too_big() Ihor Solodrai
2026-02-20 22:25 ` [PATCH bpf v3 07/15] veristat: Fix a memory leak for preset ENUMERATOR Ihor Solodrai
2026-02-20 22:25 ` [PATCH bpf v3 08/15] selftests/bpf: Fix use-after-free in xdp_metadata test Ihor Solodrai
2026-02-20 22:25 ` [PATCH bpf v3 09/15] selftests/bpf: Fix double thread join in uprobe_multi_test Ihor Solodrai
2026-02-20 22:25 ` [PATCH bpf v3 10/15] selftests/bpf: Fix resource leaks caused by missing cleanups Ihor Solodrai
2026-02-20 22:26 ` [PATCH bpf v3 11/15] selftests/bpf: Free bpf_object in test_sysctl Ihor Solodrai
2026-02-20 22:26 ` [PATCH bpf v3 12/15] selftests/bpf: Fix array bounds warning in jit_disasm_helpers Ihor Solodrai
2026-02-20 22:26 ` [PATCH bpf v3 13/15] selftests/bpf: Fix out-of-bounds array access bugs reported by ASAN Ihor Solodrai
2026-02-20 22:26 ` [PATCH bpf v3 14/15] selftests/bpf: Check BPFTOOL env var in detect_bpftool_path() Ihor Solodrai
2026-02-20 22:26 ` [PATCH bpf v3 15/15] selftests/bpf: Don't override SIGSEGV handler with ASAN Ihor Solodrai
2026-02-21 0:52 ` Eduard Zingerman
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