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bh=5XY99hVS9yq4YHWv0NyUo7LsqeDBpS85jO1WJl2092g=; b=XwD7zxjUErr+50B1MZYszB+/JmcDFKepEx+Qo2wG6c0lArc+5glU2l2tnQECMCLD2G mvH8P0daJ3rX44ZSdmrTc3yXeKw0WAvmfj2crTw9YOgWyTpl6igR3/OKUVDrEfegb0rM FImFE7dRzgOioxL/bs3gFJ4icc1QgX5hgfxx+UTRFkBHw4YmKM7DrybDrOtRxzPgBgx5 DlLfL1NPHaC6dnPGlkEVFmjCBp1rbvzSx4XGbi0W84EARf70vJ3aeTyR8fuPn7KXDkzh G9ZCrYt06gTGAUO6lengyJExxOWSZCEceqWfht0GPQfnXHpq9AEp4dqt/xMM062BoFnE /y8w== X-Gm-Message-State: AOAM532ZwImmqAFYPzTUD4RY5w7evMWxV/xRnh6fdZ9IACGbwxvAEseK 68UWSM+/Ni/h+2qyHKTchKVeJndpTGwLY70HEPY= X-Google-Smtp-Source: ABdhPJyzElvI7RLtyIMkDldepWKdYAhxTmBUIz0Yh8D31khrpK/qgPuGbFTpdG/pHphs8WZuIiqC7pEan6xnICgSpj8= X-Received: by 2002:a05:6902:1144:: with SMTP id p4mr7022759ybu.510.1619200809234; Fri, 23 Apr 2021 11:00:09 -0700 (PDT) MIME-Version: 1.0 References: <20210416202404.3443623-1-andrii@kernel.org> <20210416202404.3443623-16-andrii@kernel.org> <3947e6ff-0b73-995e-630f-4a1252f8694b@fb.com> <94f367e9-24f0-5ba6-eb8d-2951dee4219a@fb.com> In-Reply-To: <94f367e9-24f0-5ba6-eb8d-2951dee4219a@fb.com> From: Andrii Nakryiko Date: Fri, 23 Apr 2021 10:59:58 -0700 Message-ID: Subject: Re: [PATCH v2 bpf-next 15/17] selftests/bpf: add function linking selftest To: Yonghong Song Cc: Andrii Nakryiko , bpf , Networking , Alexei Starovoitov , Daniel Borkmann , Kernel Team Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Fri, Apr 23, 2021 at 10:58 AM Yonghong Song wrote: > > > > On 4/23/21 10:55 AM, Andrii Nakryiko wrote: > > On Fri, Apr 23, 2021 at 10:35 AM Yonghong Song wrote: > >> > >> > >> > >> On 4/23/21 10:18 AM, Andrii Nakryiko wrote: > >>> On Thu, Apr 22, 2021 at 5:50 PM Yonghong Song 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 > >>>> > >>>> Ack with a small nit below. > >>>> > >>>> Acked-by: Yonghong Song > >>>> > >>>>> --- > >>>>> 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 > >>>>> +#include > >>>>> +#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 > >>>>> +#include > >>>>> + > >>>>> +/* 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); > >>>>> + > >>>> [...]