Re: [PATCH] tools/perf: build issues with Clang on arm64 and CFLAGS

Arnaldo Carvalho de Melo
2021-05-10T13:02:14Z

Em Fri, May 07, 2021 at 05:54:25PM +0900, Masami Hiramatsu escreveu:
> Hi Arnaldo,
>
> Recently, I tested the perf build by clang on arm64 and found an issue

Cross building? What toolchain? I regularly build perf with lots of
clang versions, but cross building with clang isn't yet performed in my
tests.

> in arch/arm64/util/kvm-stat.c, related to missing-field-initializers warning.
>
> ----
> tools/perf $ make CC=clang LLVM=1
> ...
> arch/arm64/util/kvm-stat.c:74:9: error: missing field 'ops' initializer [-Werror,-Wmissing-field-initializers]
> { NULL },
> ^
> 1 error generated.
> ----
>
> That error itself can be fixed easily by just adding field initializers
> [1/1] Note that I didn't add Fixes tag, because I'm not sure clang build
> of perf is officially supported or not, and this seems correct C code
> to initialize a data structure with zero.(*)

I'd say it is supported, at least by me, for quite a while, as can be
seen in all pull requests I send upstream, for instance:

https://lore.kernel.org/linux-perf-users/YIxSJ7bdtjv4wHok@kernel.org/

# export PERF_TARBALL=http://192.168.86.5/perf/perf-5.12.0.tar.xz
# dm
1 72.92 alpine:3.4 : Ok gcc (Alpine 5.3.0) 5.3.0 , clang version 3.8.0 (tags/RELEASE_380/final)
2 74.56 alpine:3.5 : Ok gcc (Alpine 6.2.1) 6.2.1 20160822 , clang version 3.8.1 (tags/RELEASE_381/final)
3 81.19 alpine:3.6 : Ok gcc (Alpine 6.3.0) 6.3.0 , clang version 4.0.0 (tags/RELEASE_400/final)
4 90.07 alpine:3.7 : Ok gcc (Alpine 6.4.0) 6.4.0 , Alpine clang version 5.0.0 (tags/RELEASE_500/final) (based on LLVM 5.0.0)
5 83.40 alpine:3.8 : Ok gcc (Alpine 6.4.0) 6.4.0 , Alpine clang version 5.0.1 (tags/RELEASE_501/final) (based on LLVM 5.0.1)
6 85.30 alpine:3.9 : Ok gcc (Alpine 8.3.0) 8.3.0 , Alpine clang version 5.0.1 (tags/RELEASE_502/final) (based on LLVM 5.0.1)
7 110.88 alpine:3.10 : Ok gcc (Alpine 8.3.0) 8.3.0 , Alpine clang version 8.0.0 (tags/RELEASE_800/final) (based on LLVM 8.0.0)
8 140.86 alpine:3.11 : Ok gcc (Alpine 9.3.0) 9.3.0 , Alpine clang version 9.0.0 (https://git.alpinelinux.org/aports f7f0d2c2b8bcd6a5843401a9a702029556492689) (based on LLVM 9.0.0)
9 127.60 alpine:3.12 : Ok gcc (Alpine 9.3.0) 9.3.0 , Alpine clang version 10.0.0 (https://gitlab.alpinelinux.org/alpine/aports.git 7445adce501f8473efdb93b17b5eaf2f1445ed4c)
10 278.42 alpine:3.13 : Ok gcc (Alpine 10.2.1_pre1) 10.2.1 20201203 , Alpine clang version 10.0.1
11 235.62 alpine:edge : Ok gcc (Alpine 10.3.1_git20210424) 10.3.1 20210424 , Alpine clang version 11.1.0
12 161.23 alt:p8 : Ok x86_64-alt-linux-gcc (GCC) 5.3.1 20151207 (ALT p8 5.3.1-alt3.M80P.1) , clang version 3.8.0 (tags/RELEASE_380/final)
13 390.70 alt:p9 : Ok x86_64-alt-linux-gcc (GCC) 8.4.1 20200305 (ALT p9 8.4.1-alt0.p9.1) , clang version 10.0.0
14 95.00 alt:sisyphus : Ok x86_64-alt-linux-gcc (GCC) 10.2.1 20210313 (ALT Sisyphus 10.2.1-alt3) , clang version 10.0.1
15 77.78 amazonlinux:1 : Ok gcc (GCC) 7.2.1 20170915 (Red Hat 7.2.1-2) , clang version 3.6.2 (tags/RELEASE_362/final)
16 103.23 amazonlinux:2 : Ok gcc (GCC) 7.3.1 20180712 (Red Hat 7.3.1-12) , clang version 7.0.1 (Amazon Linux 2 7.0.1-1.amzn2.0.2)
17 22.16 android-ndk:r12b-arm : Ok arm-linux-androideabi-gcc (GCC) 4.9.x 20150123 (prerelease)
18 22.10 android-ndk:r15c-arm : Ok arm-linux-androideabi-gcc (GCC) 4.9.x 20150123 (prerelease)
19 25.74 centos:6 : Ok gcc (GCC) 4.4.7 20120313 (Red Hat 4.4.7-23)
20 31.40 centos:7 : Ok gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-44)
21 97.31 centos:8 : Ok gcc (GCC) 8.3.1 20191121 (Red Hat 8.3.1-5) , clang version 10.0.1 (Red Hat 10.0.1-1.module_el8.3.0+467+cb298d5b)
22 60.94 clearlinux:latest : Ok gcc (Clear Linux OS for Intel Architecture) 10.2.1 20201217 releases/gcc-10.2.0-643-g7cbb07d2fc , clang version 10.0.1
23 77.23 debian:8 : Ok gcc (Debian 4.9.2-10+deb8u2) 4.9.2 , Debian clang version 3.5.0-10 (tags/RELEASE_350/final) (based on LLVM 3.5.0)
24 82.00 debian:9 : Ok gcc (Debian 6.3.0-18+deb9u1) 6.3.0 20170516 , clang version 3.8.1-24 (tags/RELEASE_381/final)
25 75.27 debian:10 : Ok gcc (Debian 8.3.0-6) 8.3.0 , clang version 7.0.1-8+deb10u2 (tags/RELEASE_701/final)
26 74.40 debian:experimental : Ok gcc (Debian 10.2.1-6) 10.2.1 20210110 , Debian clang version 11.0.1-2
27 32.81 debian:experimental-x-arm64 : Ok aarch64-linux-gnu-gcc (Debian 10.2.1-6) 10.2.1 20210110
28 28.53 debian:experimental-x-mips : Ok mips-linux-gnu-gcc (Debian 10.2.1-3) 10.2.1 20201224
29 30.96 debian:experimental-x-mips64 : Ok mips64-linux-gnuabi64-gcc (Debian 10.2.1-3) 10.2.1 20201224
30 31.13 debian:experimental-x-mipsel : Ok mipsel-linux-gnu-gcc (Debian 10.2.1-3) 10.2.1 20201224
31 29.13 fedora:20 : Ok gcc (GCC) 4.8.3 20140911 (Red Hat 4.8.3-7)
32 29.51 fedora:22 : Ok gcc (GCC) 5.3.1 20160406 (Red Hat 5.3.1-6) , clang version 3.5.0 (tags/RELEASE_350/final)
33 68.17 fedora:23 : Ok gcc (GCC) 5.3.1 20160406 (Red Hat 5.3.1-6) , clang version 3.7.0 (tags/RELEASE_370/final)
34 80.83 fedora:24 : Ok gcc (GCC) 6.3.1 20161221 (Red Hat 6.3.1-1) , clang version 3.8.1 (tags/RELEASE_381/final)
35 26.32 fedora:24-x-ARC-uClibc : Ok arc-linux-gcc (ARCompact ISA Linux uClibc toolchain 2017.09-rc2) 7.1.1 20170710
36 82.85 fedora:25 : Ok gcc (GCC) 6.4.1 20170727 (Red Hat 6.4.1-1) , clang version 3.9.1 (tags/RELEASE_391/final)
37 94.47 fedora:26 : Ok gcc (GCC) 7.3.1 20180130 (Red Hat 7.3.1-2) , clang version 4.0.1 (tags/RELEASE_401/final)
38 96.40 fedora:27 : Ok gcc (GCC) 7.3.1 20180712 (Red Hat 7.3.1-6) , clang version 5.0.2 (tags/RELEASE_502/final)
39 108.54 fedora:28 : Ok gcc (GCC) 8.3.1 20190223 (Red Hat 8.3.1-2) , clang version 6.0.1 (tags/RELEASE_601/final)
40 113.97 fedora:29 : Ok gcc (GCC) 8.3.1 20190223 (Red Hat 8.3.1-2) , clang version 7.0.1 (Fedora 7.0.1-6.fc29)
41 119.26 fedora:30 : Ok gcc (GCC) 9.3.1 20200408 (Red Hat 9.3.1-2) , clang version 8.0.0 (Fedora 8.0.0-3.fc30)
42 25.92 fedora:30-x-ARC-uClibc : Ok arc-linux-gcc (ARCv2 ISA Linux uClibc toolchain 2019.03-rc1) 8.3.1 20190225
43 117.82 fedora:31 : Ok gcc (GCC) 9.3.1 20200408 (Red Hat 9.3.1-2) , clang version 9.0.1 (Fedora 9.0.1-4.fc31)
44 97.12 fedora:32 : Ok gcc (GCC) 10.2.1 20201125 (Red Hat 10.2.1-9) , clang version 10.0.1 (Fedora 10.0.1-3.fc32)
45 94.80 fedora:33 : Ok gcc (GCC) 10.3.1 20210422 (Red Hat 10.3.1-1) , clang version 11.0.0 (Fedora 11.0.0-2.fc33)
46 99.46 fedora:34 : Ok gcc (GCC) 11.0.1 20210324 (Red Hat 11.0.1-0) , clang version 12.0.0 (Fedora 12.0.0-0.3.rc1.fc34)
47 98.91 fedora:rawhide : Ok gcc (GCC) 11.0.1 20210423 (Red Hat 11.0.1-0) , clang version 12.0.0 (Fedora 12.0.0-1.fc35)
48 34.11 gentoo-stage3-amd64:latest : Ok gcc (Gentoo 9.3.0-r1 p3) 9.3.0
49 66.98 mageia:5 : Ok gcc (GCC) 4.9.2 , clang version 3.5.2 (tags/RELEASE_352/final)
50 83.81 mageia:6 : Ok gcc (Mageia 5.5.0-1.mga6) 5.5.0 , clang version 3.9.1 (tags/RELEASE_391/final)
51 48.52 mageia:7 : FAIL clang version 8.0.0 (Mageia 8.0.0-1.mga7)
yychar = yylex (&yylval, &yylloc, scanner);
^
#define yylex parse_events_lex
^
1 error generated.
make[3]: *** [/git/perf-5.12.0/tools/build/Makefile.build:139: util] Error 2
52 221.66 openmandriva:cooker : Ok gcc (GCC) 10.3.0 20210408 (OpenMandriva) , OpenMandriva 12.0.0-1 clang version 12.0.0 (/builddir/build/BUILD/llvm-project-llvmorg-12.0.0/clang b3a1e025e0452bb54d01ab5281bbf509ac4e3c72)
53 119.19 opensuse:15.0 : Ok gcc (SUSE Linux) 7.4.1 20190905 [gcc-7-branch revision 275407] , clang version 5.0.1 (tags/RELEASE_501/final 312548)
54 127.85 opensuse:15.1 : Ok gcc (SUSE Linux) 7.5.0 , clang version 7.0.1 (tags/RELEASE_701/final 349238)
55 117.53 opensuse:15.2 : Ok gcc (SUSE Linux) 7.5.0 , clang version 9.0.1
56 131.22 opensuse:15.3 : Ok gcc (SUSE Linux) 7.5.0 , clang version 7.0.1 (tags/RELEASE_701/final 349238)
57 114.64 opensuse:42.3 : Ok gcc (SUSE Linux) 4.8.5 , clang version 3.8.0 (tags/RELEASE_380/final 262553)
58 108.83 opensuse:tumbleweed : Ok gcc (SUSE Linux) 10.2.1 20200825 [revision c0746a1beb1ba073c7981eb09f55b3d993b32e5c] , clang version 10.0.1
59 25.02 oraclelinux:6 : Ok gcc (GCC) 4.4.7 20120313 (Red Hat 4.4.7-23.0.1)
60 30.76 oraclelinux:7 : Ok gcc (GCC) 4.8.5 20150623 (Red Hat 4.8.5-44.0.3)
61 95.29 oraclelinux:8 : Ok gcc (GCC) 8.3.1 20191121 (Red Hat 8.3.1-5.0.2) , clang version 10.0.1 (Red Hat 10.0.1-1.0.1.module+el8.3.0+7827+89335dbf)
62 25.85 ubuntu:12.04 : Ok gcc (Ubuntu/Linaro 4.6.3-1ubuntu5) 4.6.3 , Ubuntu clang version 3.0-6ubuntu3 (tags/RELEASE_30/final) (based on LLVM 3.0)
63 29.09 ubuntu:14.04 : Ok gcc (Ubuntu 4.8.4-2ubuntu1~14.04.4) 4.8.4
64 81.27 ubuntu:16.04 : Ok gcc (Ubuntu 5.4.0-6ubuntu1~16.04.12) 5.4.0 20160609 , clang version 3.8.0-2ubuntu4 (tags/RELEASE_380/final)
65 27.09 ubuntu:16.04-x-arm : Ok arm-linux-gnueabihf-gcc (Ubuntu/Linaro 5.4.0-6ubuntu1~16.04.9) 5.4.0 20160609
66 27.59 ubuntu:16.04-x-arm64 : Ok aarch64-linux-gnu-gcc (Ubuntu/Linaro 5.4.0-6ubuntu1~16.04.9) 5.4.0 20160609
67 26.25 ubuntu:16.04-x-powerpc : Ok powerpc-linux-gnu-gcc (Ubuntu 5.4.0-6ubuntu1~16.04.9) 5.4.0 20160609
68 26.87 ubuntu:16.04-x-powerpc64 : Ok powerpc64-linux-gnu-gcc (Ubuntu/IBM 5.4.0-6ubuntu1~16.04.9) 5.4.0 20160609
69 27.69 ubuntu:16.04-x-powerpc64el : Ok powerpc64le-linux-gnu-gcc (Ubuntu/IBM 5.4.0-6ubuntu1~16.04.9) 5.4.0 20160609
70 26.58 ubuntu:16.04-x-s390 : Ok s390x-linux-gnu-gcc (Ubuntu 5.4.0-6ubuntu1~16.04.9) 5.4.0 20160609
71 88.21 ubuntu:18.04 : Ok gcc (Ubuntu 7.5.0-3ubuntu1~18.04) 7.5.0 , clang version 6.0.0-1ubuntu2 (tags/RELEASE_600/final)
72 28.46 ubuntu:18.04-x-arm : Ok arm-linux-gnueabihf-gcc (Ubuntu/Linaro 7.5.0-3ubuntu1~18.04) 7.5.0
73 29.25 ubuntu:18.04-x-arm64 : Ok aarch64-linux-gnu-gcc (Ubuntu/Linaro 7.5.0-3ubuntu1~18.04) 7.5.0
74 23.59 ubuntu:18.04-x-m68k : Ok m68k-linux-gnu-gcc (Ubuntu 7.5.0-3ubuntu1~18.04) 7.5.0
75 27.97 ubuntu:18.04-x-powerpc : Ok powerpc-linux-gnu-gcc (Ubuntu 7.5.0-3ubuntu1~18.04) 7.5.0
76 29.83 ubuntu:18.04-x-powerpc64 : Ok powerpc64-linux-gnu-gcc (Ubuntu 7.5.0-3ubuntu1~18.04) 7.5.0
77 30.41 ubuntu:18.04-x-powerpc64el : Ok powerpc64le-linux-gnu-gcc (Ubuntu 7.5.0-3ubuntu1~18.04) 7.5.0
78 172.25 ubuntu:18.04-x-riscv64 : Ok riscv64-linux-gnu-gcc (Ubuntu 7.5.0-3ubuntu1~18.04) 7.5.0
79 26.09 ubuntu:18.04-x-s390 : Ok s390x-linux-gnu-gcc (Ubuntu 7.5.0-3ubuntu1~18.04) 7.5.0
80 28.18 ubuntu:18.04-x-sh4 : Ok sh4-linux-gnu-gcc (Ubuntu 7.5.0-3ubuntu1~18.04) 7.5.0
81 26.43 ubuntu:18.04-x-sparc64 : Ok sparc64-linux-gnu-gcc (Ubuntu 7.5.0-3ubuntu1~18.04) 7.5.0
82 76.46 ubuntu:20.04 : Ok gcc (Ubuntu 9.3.0-17ubuntu1~20.04) 9.3.0 , clang version 10.0.0-4ubuntu1
83 31.35 ubuntu:20.04-x-powerpc64el : Ok powerpc64le-linux-gnu-gcc (Ubuntu 10.2.0-5ubuntu1~20.04) 10.2.0
84 74.85 ubuntu:20.10 : Ok gcc (Ubuntu 10.2.0-13ubuntu1) 10.2.0 , Ubuntu clang version 11.0.0-2
85 71.63 ubuntu:21.04 : Ok gcc (Ubuntu 10.3.0-1ubuntu1) 10.3.0 , Ubuntu clang version 12.0.0-1ubuntu1

But I couldn't find so far, and I haven't researched this lately, a distro that has all the
devel packages cross-built so that I could cross build a full featured perf tool, are you
aware of one? In the -x-ARCH tests above I end up just manually cross-building elfutils and zlib
to get a minimal perf cross build.

> And while investigating the error, I found another issue in the Makefile.config.
>
> It seems to make CFLAGS from CORE_CFLAGS, INC_FLAGS, EXTRA_CFLAGS, EXTRA_WARNINGS
> in the following order;
>
> CFLAGS = $EXTRA_CFLAGS $EXTRA_WARNINGS $CORE_CFLAGS $INC_FLAGS
>
> But since CORE_CFLAGS includes -Wall and -Wextra, the other -Wno-XXXX in
> EXTRA_CFLAGS and EXTRA_WARNINGS are overriden and ignored.
> So, I think it is better to define it as
>
> CFLAGS = $CORE_CFLAGS $INC_FLAGS $EXTRA_CFLAGS $EXTRA_WARNINGS
>
> But I also saw some configs tweaks CFLAGS directly. I think they should
> modify EXTRA_CFLAGS.
>
> My question is that this order is intentional or not. I might
> miss something on it.

Oh the joy with Makefiles.. Most likely unintentional, please submit a patch, please reuse
your wording above to justify it.

> (*) BTW, there seems a discussion on the clang warning behavior,
> because gcc doesn't warn it anymore
> (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=36750).
> It might be better to add -Wno-missing-field-initializers in case
> of CC=clang by default.

Humm, unsure about that, I applied your patch, but I'd say it'd be better to
use the variant that initialized the first field to zero/NULL and then all the
other (not explicitely initialized) ones will be zeroed.

>
> Thank you,
>
> ---
>
> Masami Hiramatsu (1):
> tools/perf: Fix a build error on arm64 with clang
>
>
> tools/perf/arch/arm64/util/kvm-stat.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> --
> Masami Hiramatsu (Linaro) <mhiramat@kernel.org>

--

- Arnaldo