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Date: Thu, 7 Jun 2018 13:07:01 -0700
From: Martin KaFai Lau <kafai@...com>
To: Arnaldo Carvalho de Melo <acme@...nel.org>
CC: <netdev@...r.kernel.org>, Alexei Starovoitov <ast@...com>,
Daniel Borkmann <daniel@...earbox.net>, <kernel-team@...com>,
Wang Nan <wangnan0@...wei.com>, Jiri Olsa <jolsa@...nel.org>,
Namhyung Kim <namhyung@...nel.org>,
Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH bpf-next v5 00/10] BTF: BPF Type Format
On Thu, Jun 07, 2018 at 04:30:29PM -0300, Arnaldo Carvalho de Melo wrote:
> Em Thu, Jun 07, 2018 at 12:05:10PM -0700, Martin KaFai Lau escreveu:
> > On Thu, Jun 07, 2018 at 11:03:37AM -0300, Arnaldo Carvalho de Melo wrote:
> > > Em Thu, Jun 07, 2018 at 10:54:01AM -0300, Arnaldo Carvalho de Melo escreveu:
> > > > Em Tue, Jun 05, 2018 at 02:25:48PM -0700, Martin KaFai Lau escreveu:
> > > > > [ btw, the latest commit (1 commit) should be 94a11b59e592 ].
>
> > > So, the commit log message for the pahole patch is non-existent:
>
> > > https://github.com/iamkafai/pahole/commit/94a11b59e5920908085bfc8d24c92f95c8ffceaf
>
> > > we should do better in describing what is done and how, I'm staring
> > > with a message you sent to the kernel part:
> > > --
> > > This patch introduces BPF Type Format (BTF).
>
> > > BTF (BPF Type Format) is the meta data format which describes
> > > the data types of BPF program/map. Hence, it basically focus
> > > on the C programming language which the modern BPF is primary
> > > using. The first use case is to provide a generic pretty print
> > > capability for a BPF map.
>
> > I will add details in the next github respin/push.
>
> Ok, but I can do that if there is nothing else to do in the code at this
> stage :-)
>
> > > Now I'm going to do the step-by-step guide on testing the feature just
> > > introduced, and will try to convert from dwarf to BTF and back, compare
> > > the pahole output for types encoded in DWARF and BTF, etc.
>
> > > If you have something ressembling this already, please share.
>
> > The pahole only has the encoder part. I tested with the verbose output
> > from the "pahole -V -J". Loading the btf to the kernel is also tested.
>
> Ok, so here it goes my first stab at testing, using perf's BPF
> integration:
>
> [root@...et bpf]# cat hello.c
> #include "stdio.h"
>
> int syscall_enter(openat)(void *ctx)
> {
> puts("Hello, world\n");
> return 0;
> }
> [root@...et bpf]# cat ~/.perfconfig
> [llvm]
> dump-obj = true
> [root@...et bpf]# perf trace -e open*,hello.c touch /tmp/hello.BTF
> LLVM: dumping hello.o
> 0.017 ( ): __bpf_stdout__:Hello, world
> 0.019 ( 0.011 ms): touch/28147 openat(dfd: CWD, filename: /etc/ld.so.cache, flags: CLOEXEC ) = 3
> 0.053 ( ): __bpf_stdout__:Hello, world
> 0.055 ( 0.011 ms): touch/28147 openat(dfd: CWD, filename: /lib64/libc.so.6, flags: CLOEXEC ) = 3
> 0.354 ( 0.012 ms): touch/28147 open(filename: /usr/lib/locale/locale-archive, flags: CLOEXEC ) = 3
> 0.411 ( ): __bpf_stdout__:Hello, world
> 0.412 ( 0.198 ms): touch/28147 openat(dfd: CWD, filename: /tmp/hello.BTF, flags: CREAT|NOCTTY|NONBLOCK|WRONLY, mode: IRUGO|IWUGO) = 3
> [root@...et bpf]#
> [root@...et bpf]# file hello.o
> hello.o: ELF 64-bit LSB relocatable, *unknown arch 0xf7* version 1 (SYSV), not stripped
> [root@...et bpf]# pahole --btf_encode hello.o
> pahole: hello.o: No debugging information found
> [root@...et bpf]#
>
> [root@...et bpf]# readelf -s hello.o
>
> Symbol table '.symtab' contains 5 entries:
> Num: Value Size Type Bind Vis Ndx Name
> 0: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND
> 1: 0000000000000000 0 NOTYPE GLOBAL DEFAULT 7 __bpf_stdout__
> 2: 0000000000000000 0 NOTYPE GLOBAL DEFAULT 5 _license
> 3: 0000000000000000 0 NOTYPE GLOBAL DEFAULT 6 _version
> 4: 0000000000000000 0 NOTYPE GLOBAL DEFAULT 3 syscall_enter_openat
> [root@...et bpf]#
> [root@...et bpf]# readelf -SW hello.o
> There are 10 section headers, starting at offset 0x1f8:
>
> Section Headers:
> [Nr] Name Type Address Off Size ES Flg Lk Inf Al
> [ 0] NULL 0000000000000000 000000 000000 00 0 0 0
> [ 1] .strtab STRTAB 0000000000000000 000178 00007f 00 0 0 1
> [ 2] .text PROGBITS 0000000000000000 000040 000000 00 AX 0 0 4
> [ 3] syscalls:sys_enter_openat PROGBITS 0000000000000000 000040 000088 00 AX 0 0 8
> [ 4] .relsyscalls:sys_enter_openat REL 0000000000000000 000168 000010 10 9 3 8
> [ 5] license PROGBITS 0000000000000000 0000c8 000004 00 WA 0 0 1
> [ 6] version PROGBITS 0000000000000000 0000cc 000004 00 WA 0 0 4
> [ 7] maps PROGBITS 0000000000000000 0000d0 000010 00 WA 0 0 4
> [ 8] .rodata.str1.1 PROGBITS 0000000000000000 0000e0 00000e 01 AMS 0 0 1
> [ 9] .symtab SYMTAB 0000000000000000 0000f0 000078 18 1 1 8
> Key to Flags:
> W (write), A (alloc), X (execute), M (merge), S (strings), I (info),
> L (link order), O (extra OS processing required), G (group), T (TLS),
> C (compressed), x (unknown), o (OS specific), E (exclude),
> p (processor specific)
> [root@...et bpf]#
>
> Humm, lemme try something, add -g to clang-opt:
>
> [root@...et bpf]# cat ~/.perfconfig
> [llvm]
> dump-obj = true
> clang-opt = -g
> [root@...et bpf]# perf trace -e open*,hello.c touch /tmp/hello.BTF
> LLVM: dumping hello.o
> 0.185 ( ): __bpf_stdout__:Hello, world
> 0.188 ( 0.009 ms): touch/19670 openat(dfd: CWD, filename: /etc/ld.so.cache, flags: CLOEXEC ) = 3
> 0.219 ( ): __bpf_stdout__:Hello, world
> 0.220 ( 0.011 ms): touch/19670 openat(dfd: CWD, filename: /lib64/libc.so.6, flags: CLOEXEC ) = 3
> 0.480 ( 0.095 ms): touch/19670 open(filename: /usr/lib/locale/locale-archive, flags: CLOEXEC ) = 3
> 0.624 ( ): __bpf_stdout__:Hello, world
> 0.626 ( 0.011 ms): touch/19670 openat(dfd: CWD, filename: /tmp/hello.BTF, flags: CREAT|NOCTTY|NONBLOCK|WRONLY, mode: IRUGO|IWUGO) = 3
> [root@...et bpf]# file hello.o
> hello.o: ELF 64-bit LSB relocatable, *unknown arch 0xf7* version 1 (SYSV), with debug_info, not stripped
> [root@...et bpf]#
>
> Much better:
>
> [root@...et bpf]# readelf -SW hello.o
> There are 25 section headers, starting at offset 0xc70:
>
> Section Headers:
> [Nr] Name Type Address Off Size ES Flg Lk Inf Al
> [ 0] NULL 0000000000000000 000000 000000 00 0 0 0
> [ 1] .strtab STRTAB 0000000000000000 000b50 000119 00 0 0 1
> [ 2] .text PROGBITS 0000000000000000 000040 000000 00 AX 0 0 4
> [ 3] syscalls:sys_enter_openat PROGBITS 0000000000000000 000040 000088 00 AX 0 0 8
> [ 4] .relsyscalls:sys_enter_openat REL 0000000000000000 000910 000010 10 24 3 8
> [ 5] license PROGBITS 0000000000000000 0000c8 000004 00 WA 0 0 1
> [ 6] version PROGBITS 0000000000000000 0000cc 000004 00 WA 0 0 4
> [ 7] maps PROGBITS 0000000000000000 0000d0 000010 00 WA 0 0 4
> [ 8] .rodata.str1.1 PROGBITS 0000000000000000 0000e0 00000e 01 AMS 0 0 1
> [ 9] .debug_str PROGBITS 0000000000000000 0000ee 00010e 01 MS 0 0 1
> [10] .debug_loc PROGBITS 0000000000000000 0001fc 000023 00 0 0 1
> [11] .debug_abbrev PROGBITS 0000000000000000 00021f 0000e3 00 0 0 1
> [12] .debug_info PROGBITS 0000000000000000 000302 00015e 00 0 0 1
> [13] .rel.debug_info REL 0000000000000000 000920 0001e0 10 24 12 8
> [14] .debug_ranges PROGBITS 0000000000000000 000460 000030 00 0 0 1
> [15] .debug_macinfo PROGBITS 0000000000000000 000490 000001 00 0 0 1
> [16] .debug_pubnames PROGBITS 0000000000000000 000491 00006e 00 0 0 1
> [17] .rel.debug_pubnames REL 0000000000000000 000b00 000010 10 24 16 8
> [18] .debug_pubtypes PROGBITS 0000000000000000 0004ff 00005a 00 0 0 1
> [19] .rel.debug_pubtypes REL 0000000000000000 000b10 000010 10 24 18 8
> [20] .debug_frame PROGBITS 0000000000000000 000560 000028 00 0 0 8
> [21] .rel.debug_frame REL 0000000000000000 000b20 000020 10 24 20 8
> [22] .debug_line PROGBITS 0000000000000000 000588 00006e 00 0 0 1
> [23] .rel.debug_line REL 0000000000000000 000b40 000010 10 24 22 8
> [24] .symtab SYMTAB 0000000000000000 0005f8 000318 18 1 29 8
> Key to Flags:
> W (write), A (alloc), X (execute), M (merge), S (strings), I (info),
> L (link order), O (extra OS processing required), G (group), T (TLS),
> C (compressed), x (unknown), o (OS specific), E (exclude),
> p (processor specific)
> [root@...et bpf]#
>
> [root@...et bpf]# readelf -s hello.o
>
> Symbol table '.symtab' contains 33 entries:
> Num: Value Size Type Bind Vis Ndx Name
> 0: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND
> 1: 0000000000000000 0 NOTYPE LOCAL DEFAULT 9
> 2: 000000000000002d 0 NOTYPE LOCAL DEFAULT 9
> 3: 0000000000000044 0 NOTYPE LOCAL DEFAULT 9
> 4: 0000000000000053 0 NOTYPE LOCAL DEFAULT 9
> 5: 000000000000005c 0 NOTYPE LOCAL DEFAULT 9
> 6: 0000000000000061 0 NOTYPE LOCAL DEFAULT 9
> 7: 000000000000006a 0 NOTYPE LOCAL DEFAULT 9
> 8: 0000000000000073 0 NOTYPE LOCAL DEFAULT 9
> 9: 0000000000000077 0 NOTYPE LOCAL DEFAULT 9
> 10: 0000000000000086 0 NOTYPE LOCAL DEFAULT 9
> 11: 000000000000008b 0 NOTYPE LOCAL DEFAULT 9
> 12: 0000000000000098 0 NOTYPE LOCAL DEFAULT 9
> 13: 00000000000000a1 0 NOTYPE LOCAL DEFAULT 9
> 14: 00000000000000ac 0 NOTYPE LOCAL DEFAULT 9
> 15: 00000000000000b8 0 NOTYPE LOCAL DEFAULT 9
> 16: 00000000000000c4 0 NOTYPE LOCAL DEFAULT 9
> 17: 00000000000000d6 0 NOTYPE LOCAL DEFAULT 9
> 18: 00000000000000e8 0 NOTYPE LOCAL DEFAULT 9
> 19: 00000000000000fd 0 NOTYPE LOCAL DEFAULT 9
> 20: 0000000000000101 0 NOTYPE LOCAL DEFAULT 9
> 21: 0000000000000107 0 NOTYPE LOCAL DEFAULT 9
> 22: 0000000000000000 0 SECTION LOCAL DEFAULT 3
> 23: 0000000000000000 0 SECTION LOCAL DEFAULT 10
> 24: 0000000000000000 0 SECTION LOCAL DEFAULT 11
> 25: 0000000000000000 0 SECTION LOCAL DEFAULT 12
> 26: 0000000000000000 0 SECTION LOCAL DEFAULT 14
> 27: 0000000000000000 0 SECTION LOCAL DEFAULT 20
> 28: 0000000000000000 0 SECTION LOCAL DEFAULT 22
> 29: 0000000000000000 0 NOTYPE GLOBAL DEFAULT 7 __bpf_stdout__
> 30: 0000000000000000 0 NOTYPE GLOBAL DEFAULT 5 _license
> 31: 0000000000000000 0 NOTYPE GLOBAL DEFAULT 6 _version
> 32: 0000000000000000 0 NOTYPE GLOBAL DEFAULT 3 syscall_enter_openat
> [root@...et bpf]#
>
> Progress:
>
> [root@...et bpf]# pahole --btf_encode hello.o
> sh: llvm-objcopy: command not found
> Failed to encode BTF
> [root@...et bpf]#
>
> [acme@...et perf]$ llvm-
> llvm-ar llvm-cov llvm-dis llvm-lib llvm-modextract llvm-profdata llvm-split
> llvm-as llvm-c-test llvm-dlltool llvm-link llvm-mt llvm-ranlib llvm-stress
> llvm-bcanalyzer llvm-cvtres llvm-dsymutil llvm-lto llvm-nm llvm-readelf llvm-strings
> llvm-cat llvm-cxxdump llvm-dwarfdump llvm-lto2 llvm-objdump llvm-readobj llvm-symbolizer
> llvm-config llvm-cxxfilt llvm-dwp llvm-mc llvm-opt-report llvm-rtdyld llvm-tblgen
> llvm-config-64 llvm-diff llvm-extract llvm-mcmarkup llvm-pdbutil llvm-size llvm-xray
> [acme@...et perf]$ llvm-
>
> So this must be available in a newer llvm version? Which one?
I should have put in the details in my last email or
in the commit message, my bad.
1. The tools/testing/selftests/bpf/Makefile has the CLANG_FLAGS and
LLC_FLAGS needed to compile the bpf prog. It requires a new
"-mattr=dwarf" llc option which was added to the future
llvm 7.0.
Hence, I have been using the llvm's master in github which
also has the llvm-objcopy.
2. The kernel's btf part only focus on the BPF map.
Hence, the testing bpf program should have the map's key
and map's value. e.g. tools/testing/selftests/bpf/test_btf_haskv.c
>
> [root@...et bpf]# clang -v
> clang version 5.0.1 (tags/RELEASE_501/final)
> Target: x86_64-unknown-linux-gnu
> Thread model: posix
> InstalledDir: /usr/bin
> Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-redhat-linux/7
> Found candidate GCC installation: /usr/lib/gcc/x86_64-redhat-linux/7
> Selected GCC installation: /usr/bin/../lib/gcc/x86_64-redhat-linux/7
> Candidate multilib: .;@m64
> Candidate multilib: 32;@m32
> Selected multilib: .;@m64
> [root@...et bpf]#
>
> [acme@...et perf]$ rpm -q clang llvm
> clang-5.0.1-5.fc27.x86_64
> llvm-5.0.1-6.fc27.x86_64
> [acme@...et perf]$
> [root@...et bpf]# clang -v
> clang version 5.0.1 (tags/RELEASE_501/final)
> Target: x86_64-unknown-linux-gnu
> Thread model: posix
> InstalledDir: /usr/bin
> Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-redhat-linux/7
> Found candidate GCC installation: /usr/lib/gcc/x86_64-redhat-linux/7
> Selected GCC installation: /usr/bin/../lib/gcc/x86_64-redhat-linux/7
> Candidate multilib: .;@m64
> Candidate multilib: 32;@m32
> Selected multilib: .;@m64
> [root@...et bpf]#
>
> [acme@...et perf]$ rpm -q clang llvm
> clang-5.0.1-5.fc27.x86_64
> llvm-5.0.1-6.fc27.x86_64
> [acme@...et perf]$
>
> - Arnaldo
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