From: Andrii Nakryiko <andrii.nakryiko@gmail.com>
To: Yonghong Song <yhs@fb.com>
Cc: Andrii Nakryiko <andrii@kernel.org>, bpf <bpf@vger.kernel.org>,
Networking <netdev@vger.kernel.org>,
Alexei Starovoitov <ast@fb.com>,
Daniel Borkmann <daniel@iogearbox.net>,
Kernel Team <kernel-team@fb.com>
Subject: Re: [PATCH v2 bpf-next 15/17] selftests/bpf: add function linking selftest
Date: Fri, 23 Apr 2021 10:59:58 -0700 [thread overview]
Message-ID: <CAEf4BzaH4Sr5HenM1+-j4d=r=juw8pacPpXZM3YBxJu2S_uPwg@mail.gmail.com> (raw)
In-Reply-To: <94f367e9-24f0-5ba6-eb8d-2951dee4219a@fb.com>
On Fri, Apr 23, 2021 at 10:58 AM Yonghong Song <yhs@fb.com> wrote:
>
>
>
> On 4/23/21 10:55 AM, Andrii Nakryiko wrote:
> > On Fri, Apr 23, 2021 at 10:35 AM Yonghong Song <yhs@fb.com> wrote:
> >>
> >>
> >>
> >> On 4/23/21 10:18 AM, Andrii Nakryiko wrote:
> >>> On Thu, Apr 22, 2021 at 5:50 PM Yonghong Song <yhs@fb.com> wrote:
> >>>>
> >>>>
> >>>>
> >>>> On 4/16/21 1:24 PM, Andrii Nakryiko wrote:
> >>>>> Add selftest validating various aspects of statically linking functions:
> >>>>> - no conflicts and correct resolution for name-conflicting static funcs;
> >>>>> - correct resolution of extern functions;
> >>>>> - correct handling of weak functions, both resolution itself and libbpf's
> >>>>> handling of unused weak function that "lost" (it leaves gaps in code with
> >>>>> no ELF symbols);
> >>>>> - correct handling of hidden visibility to turn global function into
> >>>>> "static" for the purpose of BPF verification.
> >>>>>
> >>>>> Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
> >>>>
> >>>> Ack with a small nit below.
> >>>>
> >>>> Acked-by: Yonghong Song <yhs@fb.com>
> >>>>
> >>>>> ---
> >>>>> tools/testing/selftests/bpf/Makefile | 3 +-
> >>>>> .../selftests/bpf/prog_tests/linked_funcs.c | 42 +++++++++++
> >>>>> .../selftests/bpf/progs/linked_funcs1.c | 73 +++++++++++++++++++
> >>>>> .../selftests/bpf/progs/linked_funcs2.c | 73 +++++++++++++++++++
> >>>>> 4 files changed, 190 insertions(+), 1 deletion(-)
> >>>>> create mode 100644 tools/testing/selftests/bpf/prog_tests/linked_funcs.c
> >>>>> create mode 100644 tools/testing/selftests/bpf/progs/linked_funcs1.c
> >>>>> create mode 100644 tools/testing/selftests/bpf/progs/linked_funcs2.c
> >>>>>
> >>>>> diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
> >>>>> index 666b462c1218..427ccfec1a6a 100644
> >>>>> --- a/tools/testing/selftests/bpf/Makefile
> >>>>> +++ b/tools/testing/selftests/bpf/Makefile
> >>>>> @@ -308,9 +308,10 @@ endef
> >>>>>
> >>>>> SKEL_BLACKLIST := btf__% test_pinning_invalid.c test_sk_assign.c
> >>>>>
> >>>>> -LINKED_SKELS := test_static_linked.skel.h
> >>>>> +LINKED_SKELS := test_static_linked.skel.h linked_funcs.skel.h
> >>>>>
> >>>>> test_static_linked.skel.h-deps := test_static_linked1.o test_static_linked2.o
> >>>>> +linked_funcs.skel.h-deps := linked_funcs1.o linked_funcs2.o
> >>>>>
> >>>>> LINKED_BPF_SRCS := $(patsubst %.o,%.c,$(foreach skel,$(LINKED_SKELS),$($(skel)-deps)))
> >>>>>
> >>>>> diff --git a/tools/testing/selftests/bpf/prog_tests/linked_funcs.c b/tools/testing/selftests/bpf/prog_tests/linked_funcs.c
> >>>>> new file mode 100644
> >>>>> index 000000000000..03bf8ef131ce
> >>>>> --- /dev/null
> >>>>> +++ b/tools/testing/selftests/bpf/prog_tests/linked_funcs.c
> >>>>> @@ -0,0 +1,42 @@
> >>>>> +// SPDX-License-Identifier: GPL-2.0
> >>>>> +/* Copyright (c) 2021 Facebook */
> >>>>> +
> >>>>> +#include <test_progs.h>
> >>>>> +#include <sys/syscall.h>
> >>>>> +#include "linked_funcs.skel.h"
> >>>>> +
> >>>>> +void test_linked_funcs(void)
> >>>>> +{
> >>>>> + int err;
> >>>>> + struct linked_funcs *skel;
> >>>>> +
> >>>>> + skel = linked_funcs__open();
> >>>>> + if (!ASSERT_OK_PTR(skel, "skel_open"))
> >>>>> + return;
> >>>>> +
> >>>>> + skel->rodata->my_tid = syscall(SYS_gettid);
> >>>>> + skel->rodata->syscall_id = SYS_getpgid;
> >>>>> +
> >>>>> + err = linked_funcs__load(skel);
> >>>>> + if (!ASSERT_OK(err, "skel_load"))
> >>>>> + goto cleanup;
> >>>>> +
> >>>>> + err = linked_funcs__attach(skel);
> >>>>> + if (!ASSERT_OK(err, "skel_attach"))
> >>>>> + goto cleanup;
> >>>>> +
> >>>>> + /* trigger */
> >>>>> + syscall(SYS_getpgid);
> >>>>> +
> >>>>> + ASSERT_EQ(skel->bss->output_val1, 2000 + 2000, "output_val1");
> >>>>> + ASSERT_EQ(skel->bss->output_ctx1, SYS_getpgid, "output_ctx1");
> >>>>> + ASSERT_EQ(skel->bss->output_weak1, 42, "output_weak1");
> >>>>> +
> >>>>> + ASSERT_EQ(skel->bss->output_val2, 2 * 1000 + 2 * (2 * 1000), "output_val2");
> >>>>> + ASSERT_EQ(skel->bss->output_ctx2, SYS_getpgid, "output_ctx2");
> >>>>> + /* output_weak2 should never be updated */
> >>>>> + ASSERT_EQ(skel->bss->output_weak2, 0, "output_weak2");
> >>>>> +
> >>>>> +cleanup:
> >>>>> + linked_funcs__destroy(skel);
> >>>>> +}
> >>>>> diff --git a/tools/testing/selftests/bpf/progs/linked_funcs1.c b/tools/testing/selftests/bpf/progs/linked_funcs1.c
> >>>>> new file mode 100644
> >>>>> index 000000000000..cc621d4e4d82
> >>>>> --- /dev/null
> >>>>> +++ b/tools/testing/selftests/bpf/progs/linked_funcs1.c
> >>>>> @@ -0,0 +1,73 @@
> >>>>> +// SPDX-License-Identifier: GPL-2.0
> >>>>> +/* Copyright (c) 2021 Facebook */
> >>>>> +
> >>>>> +#include "vmlinux.h"
> >>>>> +#include <bpf/bpf_helpers.h>
> >>>>> +#include <bpf/bpf_tracing.h>
> >>>>> +
> >>>>> +/* weak and shared between two files */
> >>>>> +const volatile int my_tid __weak = 0;
> >>>>> +const volatile long syscall_id __weak = 0;
> >>>>
> >>>> Since the new compiler (llvm13) is recommended for this patch set.
> >>>> We can simplify the above two definition with
> >>>> int my_tid __weak;
> >>>> long syscall_id __weak;
> >>>> The same for the other file.
> >>>
> >>> This is not about old vs new compilers. I wanted to use .rodata
> >>> variables, but I'll switch to .bss, no problem.
> >>
> >> I see. You can actually hone one "const volatile ing my_tid __weak = 0"
> >> and another "long syscall_id __weak". This way, you will be able to
> >> test both .rodata and .bss section.
> >
> > I wonder if you meant to have one my_tid __weak in .bss and another
> > my_tid __weak in .rodata. Or just my_tid in .bss and syscall_id in
> > .rodata?
> >
> > If the former (mixing ELF sections across definitions of the same
> > symbol), then it's disallowed right now. libbpf will error out on
> > mismatched sections. I tested this with normal compilation, it does
> > work and the final section is the section of the winner.
> >
> > But I think that's quite confusing, actually, so I'm going to leave it
> > disallowed for now. E.g., if one file expects a read-write variable
> > and another expects that same variable to be read-only, and the winner
> > ends up being read-only one, then the file expecting read-write will
> > essentially have incorrect code (and will be rejected by BPF verifier,
> > if anything attempts to write). So I think it's better to reject it at
> > the linking time.
> >
> > But I'll do one (my_tid) as .bss, and another (syscall_id) as .rodata.
>
> I mean this one. Permitting the same variable in both .bss and .rodata
> sections is never a good practice.
Ok, cool, that's what we do right now. I wonder why it is allowed by
user-space linkers, it seems dangerous.
>
> >
> >>
> >>>
> >>>>
> >>>> But I am also okay with the current form
> >>>> to *satisfy* llvm10 some people may still use.
> >>>>
> >>>>> +
> >>>>> +int output_val1 = 0;
> >>>>> +int output_ctx1 = 0;
> >>>>> +int output_weak1 = 0;
> >>>>> +
> >>>>> +/* same "subprog" name in all files, but it's ok because they all are static */
> >>>>> +static __noinline int subprog(int x)
> >>>>> +{
> >>>>> + /* but different formula */
> >>>>> + return x * 1;
> >>>>> +}
> >>>>> +
> >>>>> +/* Global functions can't be void */
> >>>>> +int set_output_val1(int x)
> >>>>> +{
> >>>>> + output_val1 = x + subprog(x);
> >>>>> + return x;
> >>>>> +}
> >>>>> +
> >>>>> +/* This function can't be verified as global, as it assumes raw_tp/sys_enter
> >>>>> + * context and accesses syscall id (second argument). So we mark it as
> >>>>> + * __hidden, so that libbpf will mark it as static in the final object file,
> >>>>> + * right before verifying it in the kernel.
> >>>>> + *
> >>>>> + * But we don't mark it as __hidden here, rather at extern site. __hidden is
> >>>>> + * "contaminating" visibility, so it will get propagated from either extern or
> >>>>> + * actual definition (including from the losing __weak definition).
> >>>>> + */
> >>>>> +void set_output_ctx1(__u64 *ctx)
> >>>>> +{
> >>>>> + output_ctx1 = ctx[1]; /* long id, same as in BPF_PROG below */
> >>>>> +}
> >>>>> +
> >>>>> +/* this weak instance should win because it's the first one */
> >>>>> +__weak int set_output_weak(int x)
> >>>>> +{
> >>>>> + output_weak1 = x;
> >>>>> + return x;
> >>>>> +}
> >>>>> +
> >>>>> +extern int set_output_val2(int x);
> >>>>> +
> >>>>> +/* here we'll force set_output_ctx2() to be __hidden in the final obj file */
> >>>>> +__hidden extern void set_output_ctx2(__u64 *ctx);
> >>>>> +
> >>>> [...]
next prev parent reply other threads:[~2021-04-23 18:00 UTC|newest]
Thread overview: 67+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-16 20:23 [PATCH v2 bpf-next 00/17] BPF static linker: support externs Andrii Nakryiko
2021-04-16 20:23 ` [PATCH v2 bpf-next 01/17] bpftool: support dumping BTF VAR's "extern" linkage Andrii Nakryiko
2021-04-22 3:02 ` Yonghong Song
2021-04-16 20:23 ` [PATCH v2 bpf-next 02/17] bpftool: dump more info about DATASEC members Andrii Nakryiko
2021-04-22 3:09 ` Yonghong Song
2021-04-16 20:23 ` [PATCH v2 bpf-next 03/17] libbpf: suppress compiler warning when using SEC() macro with externs Andrii Nakryiko
2021-04-22 3:47 ` Yonghong Song
2021-04-22 3:59 ` Andrii Nakryiko
2021-04-16 20:23 ` [PATCH v2 bpf-next 04/17] libbpf: mark BPF subprogs with hidden visibility as static for BPF verifier Andrii Nakryiko
2021-04-22 5:43 ` Yonghong Song
2021-04-22 18:09 ` Andrii Nakryiko
2021-04-22 23:00 ` Yonghong Song
2021-04-22 23:28 ` Andrii Nakryiko
2021-04-16 20:23 ` [PATCH v2 bpf-next 05/17] libbpf: allow gaps in BPF program sections to support overriden weak functions Andrii Nakryiko
2021-04-22 6:25 ` Yonghong Song
2021-04-22 18:10 ` Andrii Nakryiko
2021-04-16 20:23 ` [PATCH v2 bpf-next 06/17] libbpf: refactor BTF map definition parsing Andrii Nakryiko
2021-04-22 15:33 ` Yonghong Song
2021-04-22 18:40 ` Andrii Nakryiko
2021-04-16 20:23 ` [PATCH v2 bpf-next 07/17] libbpf: factor out symtab and relos sanity checks Andrii Nakryiko
2021-04-22 16:06 ` Yonghong Song
2021-04-22 18:16 ` Andrii Nakryiko
2021-04-16 20:23 ` [PATCH v2 bpf-next 08/17] libbpf: make few internal helpers available outside of libbpf.c Andrii Nakryiko
2021-04-22 16:19 ` Yonghong Song
2021-04-22 18:18 ` Andrii Nakryiko
2021-04-16 20:23 ` [PATCH v2 bpf-next 09/17] libbpf: extend sanity checking ELF symbols with externs validation Andrii Nakryiko
2021-04-22 16:35 ` Yonghong Song
2021-04-22 18:20 ` Andrii Nakryiko
2021-04-22 23:13 ` Yonghong Song
2021-04-16 20:23 ` [PATCH v2 bpf-next 10/17] libbpf: tighten BTF type ID rewriting with error checking Andrii Nakryiko
2021-04-22 16:50 ` Yonghong Song
2021-04-22 18:24 ` Andrii Nakryiko
2021-04-23 2:54 ` Alexei Starovoitov
2021-04-23 4:25 ` Andrii Nakryiko
2021-04-23 5:11 ` Alexei Starovoitov
2021-04-23 16:09 ` Andrii Nakryiko
2021-04-23 16:18 ` Alexei Starovoitov
2021-04-23 16:30 ` Andrii Nakryiko
2021-04-23 16:34 ` Alexei Starovoitov
2021-04-23 17:02 ` Andrii Nakryiko
2021-04-16 20:23 ` [PATCH v2 bpf-next 11/17] libbpf: add linker extern resolution support for functions and global variables Andrii Nakryiko
2021-04-22 21:27 ` Yonghong Song
2021-04-22 22:12 ` Andrii Nakryiko
2021-04-22 23:57 ` Yonghong Song
2021-04-23 2:36 ` Yonghong Song
2021-04-23 4:28 ` Andrii Nakryiko
2021-04-23 4:27 ` Andrii Nakryiko
2021-04-16 20:23 ` [PATCH v2 bpf-next 12/17] libbpf: support extern resolution for BTF-defined maps in .maps section Andrii Nakryiko
2021-04-22 22:56 ` Yonghong Song
2021-04-22 23:32 ` Andrii Nakryiko
2021-04-16 20:24 ` [PATCH v2 bpf-next 13/17] selftests/bpf: use -O0 instead of -Og in selftests builds Andrii Nakryiko
2021-04-23 0:05 ` Yonghong Song
2021-04-16 20:24 ` [PATCH v2 bpf-next 14/17] selftests/bpf: omit skeleton generation for multi-linked BPF object files Andrii Nakryiko
2021-04-23 0:13 ` Yonghong Song
2021-04-16 20:24 ` [PATCH v2 bpf-next 15/17] selftests/bpf: add function linking selftest Andrii Nakryiko
2021-04-23 0:50 ` Yonghong Song
2021-04-23 2:34 ` Alexei Starovoitov
2021-04-23 4:29 ` Andrii Nakryiko
2021-04-23 17:18 ` Andrii Nakryiko
2021-04-23 17:35 ` Yonghong Song
2021-04-23 17:55 ` Andrii Nakryiko
2021-04-23 17:58 ` Yonghong Song
2021-04-23 17:59 ` Andrii Nakryiko [this message]
2021-04-16 20:24 ` [PATCH v2 bpf-next 16/17] selftests/bpf: add global variables " Andrii Nakryiko
2021-04-23 1:01 ` Yonghong Song
2021-04-16 20:24 ` [PATCH v2 bpf-next 17/17] sleftests/bpf: add map " Andrii Nakryiko
2021-04-23 1:20 ` Yonghong Song
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