Re: [PATCH] gcc-plugins: simplify GCC plugin-dev capability test

On 18/12/2020 15:12, Jon Hunter wrote:

On 18/12/2020 15:09, Marek Szyprowski wrote:

quoted

On 18.12.2020 16:03, Jon Hunter wrote:

quoted

On 18/12/2020 10:05, Marek Szyprowski wrote:

quoted

On 18.12.2020 10:43, Masahiro Yamada wrote:

quoted

On Fri, Dec 18, 2020 at 4:58 PM Marek Szyprowski
[off-list ref] wrote:

quoted

On 03.12.2020 13:57, Masahiro Yamada wrote:

quoted

Linus pointed out a third of the time in the Kconfig parse stage comes
from the single invocation of cc1plus in scripts/gcc-plugin.sh [1],
and directly testing plugin-version.h for existence cuts down the
overhead a lot. [2]

This commit takes one step further to kill the build test entirely.

The small piece of code was probably intended to test the C++ designated
initializer, which was not supported until C++20.

In fact, with -pedantic option given, both GCC and Clang emit a warning.

$ echo 'class test { public: int test; } test = { .test = 1 };' | g++ -x c++ -pedantic - -fsyntax-only
<stdin>:1:43: warning: C++ designated initializers only available with '-std=c++2a' or '-std=gnu++2a' [-Wpedantic]
$ echo 'class test { public: int test; } test = { .test = 1 };' | clang++ -x c++ -pedantic - -fsyntax-only
<stdin>:1:43: warning: designated initializers are a C++20 extension [-Wc++20-designator]
class test { public: int test; } test = { .test = 1 };
                                             ^
1 warning generated.

Otherwise, modern C++ compilers should be able to build the code, and
hopefully skipping this test should not make any practical problem.

Checking the existence of plugin-version.h is still needed to ensure
the plugin-dev package is installed. The test code is now small enough
to be embedded in scripts/gcc-plugins/Kconfig.

[1] https://protect2.fireeye.com/v1/url?k=03db90e1-5c40a828-03da1bae-0cc47a336fae-4cc36f5830aeb78d&q=1&e=dfdc1cf9-82d6-4ca5-b35d-1782e918bde3&u=https%3A%2F%2Flore.kernel.org%2Flkml%2FCAHk-%3DwjU4DCuwQ4pXshRbwDCUQB31ScaeuDo1tjoZ0_PjhLHzQ%40mail.gmail.com%2F
[2] https://protect2.fireeye.com/v1/url?k=965b670a-c9c05fc3-965aec45-0cc47a336fae-e34339513ff747c0&q=1&e=dfdc1cf9-82d6-4ca5-b35d-1782e918bde3&u=https%3A%2F%2Flore.kernel.org%2Flkml%2FCAHk-%3DwhK0aQxs6Q5ijJmYF1n2ch8cVFSUzU5yUM_HOjig%3D%2Bvnw%40mail.gmail.com%2F

Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

This patch landed in linux next-20201217 as commit 1e860048c53e
("gcc-plugins: simplify GCC plugin-dev capability test").

It causes a build break with my tests setup, but I'm not sure weather it
is really an issue of this commit or a toolchain I use. However I've
checked various versions of the gcc cross-compilers released by Linaro
at https://protect2.fireeye.com/v1/url?k=053727b6-5aac1f7f-0536acf9-0cc47a336fae-5bd799e7ce6b1b9b&q=1&e=dfdc1cf9-82d6-4ca5-b35d-1782e918bde3&u=https%3A%2F%2Freleases.linaro.org%2Fcomponents%2Ftoolchain%2Fbinaries%2F and all
fails with the same error:

$ make ARCH=arm
CROSS_COMPILE=../../cross/gcc-arm-10.2-2020.11-x86_64-arm-none-eabi/bin/arm-none-eabi-
zImage
     HOSTCXX scripts/gcc-plugins/arm_ssp_per_task_plugin.so
In file included from
/home/mszyprow/dev/cross/gcc-arm-10.2-2020.11-x86_64-arm-none-eabi/bin/../lib/gcc/arm-none-eabi/10.2.1/plugin/include/gcc-plugin.h:28:0,
                    from scripts/gcc-plugins/gcc-common.h:7,
                    from scripts/gcc-plugins/arm_ssp_per_task_plugin.c:3:
/home/mszyprow/dev/cross/gcc-arm-10.2-2020.11-x86_64-arm-none-eabi/bin/../lib/gcc/arm-none-eabi/10.2.1/plugin/include/system.h:687:10:
fatal error: gmp.h: No such file or directory
    #include <gmp.h>
             ^~~~~~~
compilation terminated.
scripts/gcc-plugins/Makefile:47: recipe for target
'scripts/gcc-plugins/arm_ssp_per_task_plugin.so' failed
make[2]: *** [scripts/gcc-plugins/arm_ssp_per_task_plugin.so] Error 1
scripts/Makefile.build:496: recipe for target 'scripts/gcc-plugins' failed
make[1]: *** [scripts/gcc-plugins] Error 2
Makefile:1190: recipe for target 'scripts' failed
make: *** [scripts] Error 2

Compilation works if I use the cross-gcc provided by
gcc-7-arm-linux-gnueabi/gcc-arm-linux-gnueabi Ubuntu packages, which is:

$ arm-linux-gnueabi-gcc --version
arm-linux-gnueabi-gcc (Ubuntu/Linaro 7.5.0-3ubuntu1~18.04) 7.5.0

I can compile gcc-plugins with Linaro toolchians.

The version of mine is this:

masahiro@oscar:~/ref/linux-next$
~/tools/arm-linaro-7.5/bin/arm-linux-gnueabihf-gcc --version
arm-linux-gnueabihf-gcc (Linaro GCC 7.5-2019.12) 7.5.0
Copyright (C) 2017 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.




Maybe, it depends on the host environment?


Please try this:

$ sudo apt install libgmp-dev

Indeed, it was missing on my setup. Sorry for the noise.

So this change also breaks the build on our farm build machines and
while we can request that packages are installed on these machines, it
takes time. Is there anyway to avoid this?

You can temporarily revert 1e860048c53e (this patch).

Again that works locally, but these automated builders just pull the
latest -next branch and build.

However, if you are saying that this is a problem/bug with our builders,
then of course we will have to get this fixed.

Jon

-- 
nvpublic