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bh=0/T8IlC4eTaPf6xmgmi85RESqkq77sy+2DF2148hbeY=; b=krshbX1btVXKHlTQMFIaNXzPpK6y7YVFu8Qkc+BvutFpTlCvKMRXAAytDUMDpexVCg QtZ+LnpsW0QyPnHPplznmcdL6GQmuwwt6pzXNn49Weyxn+D6neNq2JIfjCTQDCVdpw4M Ywi+hYVONN7B+F12BSEMqYUUf8n+IWkR5EOMb7PolAXreNmyhAOI6oe9c6zacvlsuFSX dn1/+REMeTiU+esNm8zlr9mQ4cjx94yIK9JsfViprngkuy2266HmXUnJq5r6cugpdIIo V/MOKVEAca6Ixk3EwRb1wR/i6AF4KD/1y1Dihf6LbRlfgJwwe8+Pyx84WPPk6LLuyAJS wtFw== X-Gm-Message-State: AOAM530WIs7gpP9hn4e20xaQkEbaX38DchFhhX65Roo16eJ5ij2xaJi1 ++22azkWpfO8r1fQn8I+GEd4RGg7G8AFmvv8JEo= X-Google-Smtp-Source: ABdhPJxo62G6/2EyHgSf2jC7Mxx5DGs5DSn8byaAm6FZ7H+TuEGOoXyETJRfPcHx+jp3shh9fxt8swA/OeYDtrdbXU0= X-Received: by 2002:a25:ba06:: with SMTP id t6mr6582299ybg.459.1619200520868; Fri, 23 Apr 2021 10:55:20 -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> In-Reply-To: From: Andrii Nakryiko Date: Fri, 23 Apr 2021 10:55:09 -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 10:35 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. > > > > >> > >> 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); > >>> + > >> [...]