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Date: Thu, 7 Jun 2018 16:30:29 -0300
From: Arnaldo Carvalho de Melo <acme@...nel.org>
To: Martin KaFai Lau <kafai@...com>
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
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?
[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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