Re: [PATCH 2/9] tests/tcg: improve check for working cross compilers

[Ilya Leoshkevich <iii@linux.ibm.com>]

On 9/14/26 18:07, Alex Bennée wrote:
> Daniel P. Berrangé <berrange@redhat.com> writes:
> 
> (trimed cc list, add Ilya)
> 
>> On Sun, Sep 13, 2026 at 10:08:52PM -0700, Pierrick Bouvier wrote:
>>> On 9/10/26 11:14 AM, Alex Bennée wrote:
>>>> From: Daniel P. Berrangé <berrange@redhat.com>
>>>>
>>>> When it finds a cross compiler, tests/tcg/meson.build tries
>>>> building test_cc.c to validate that the compiler works. This
>>>> includes "stdint.h" as a witness for working C library, however,
>>>> that is not a good choice as it can be provided by the toolchain
>>>> alone:
>>>>
>>>>     $ rpm -ql gcc-s390x-linux-gnu  | grep /stdint.h
>>>>     /usr/lib/gcc/s390x-linux-gnu/16/include/stdint.h
>>>>
>>>> As a result, if you install the s390x GCC cross compiler, but
>>>> not any C library, meson decides to use the host compiler instead
>>>> of the container:
>>>>
>>>>       cc for aarch64-softmmu          : aarch64-linux-gnu-gcc (from 'debian-all-test-cross' container)
>>>>       cc for loongarch64-softmmu      : loongarch64-unknown-linux-gnu-gcc (from 'debian-loongarch-cross' container)
>>>>       cc for riscv64-softmmu          : riscv64-linux-gnu-gcc (from 'debian-all-test-cross' container)
>>>>       cc for s390x-softmmu            : s390x-linux-gnu-gcc
>>>>       cc for x86_64-softmmu           : x86_64-linux-gnu-gcc (from 'debian-amd64-cross' container)
>>>>
>>>> Eventually this results in failure to run 'make check':
>>>>
>>>> [33/40] Generating tests/tcg/s390x-softmmu-hello with a custom command
>>>> FAILED: [code=1] tests/tcg/s390x-softmmu-hello.test
>>>> /usr/bin/s390x-linux-gnu-gcc /home/berrange/src/virt/qemu/tests/tcg/multiarch/system/hello.c -o tests/tcg/s390x-softmmu-hello.test -static -MMD -MF tests/tcg/s390x-softmmu-hello.d -Wall -Werror -O0 -g -fno-strict-aliasing -nostdlib -ffreestanding -Wa,--noexecstack -I /home/berrange/src/virt/qemu/tests/tcg/s390x/system/../../minilib /home/berrange/src/virt/qemu/tests/tcg/s390x/system/../../minilib/printf.c -I /home/berrange/src/virt/qemu/include/hw/s390x/ipl -march=z13 ../tests/tcg/s390x/system/../head64.S ../tests/tcg/s390x/system/../console.c
>>>> In file included from ../tests/tcg/s390x/system/../console.c:8:
>>>> ../tests/tcg/s390x/system/../../../../pc-bios/s390-ccw/sclp.c:11:10: fatal error: string.h: No such file or directory
>>>>      11 | #include <string.h>
>>>>         |          ^~~~~~~~~~
>>>> compilation terminated.
>>>>
>>>> Adding more include files to the test program ensures the
>>>> meson probe makes a better decision.
>>>>
>>>> Fixes: e5d084d622b1 (tests/tcg/meson.build: check host cross cc is working)
>>>> Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
>>>> Message-ID: <20260910100120.2076092-1-berrange@redhat.com>
>>>> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
>>>> ---
>>>>    tests/tcg/test_cc.c | 6 +++++-
>>>>    1 file changed, 5 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/tests/tcg/test_cc.c b/tests/tcg/test_cc.c
>>>> index d3614a01fe6..fafee055b40 100644
>>>> --- a/tests/tcg/test_cc.c
>>>> +++ b/tests/tcg/test_cc.c
>>>> @@ -1,7 +1,11 @@
>>>>    /* SPDX-License-Identifier: GPL-2.0-or-later */
>>>> -/* Include a standard header to make sure cross compiler provides them */
>>>> +/* Use some standard headers to ensure the cross compiler provides them */
>>>>    #include <stdint.h>
>>>> +#include <string.h>
>>>> +#include <stdbool.h>
>>>> +#include <stddef.h>
>>>> +#include <stdio.h>
>>>>    int main(void)
>>>>    {
>>>
>>> Ideally, we should do separate tests for system vs user tests.
>>> System ones are always compiled with -ffreestanding, while user ones should
>>> provide a C library.
>>>
>>>  From this standard:
>>>
>>> https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2023/p2338r3.html
>>> ```
>>> A freestanding C implementation is required to provide the entirety of the
>>> following headers:
>>>
>>> <float.h>
>>> <iso646.h>
>>> <limits.h>
>>> <stdalign.h>
>>> <stdarg.h>
>>> <stdbool.h>
>>> <stddef.h>
>>> <stdint.h>
>>> <stdnoreturn.h>
>>> Most of <string.h> is required (strdup, strndup, strcoll, strxfrm, and
>>> strerror are excluded). This includes strtok, which requires global data.
>>> ```
>>>
>>> Maybe for now we can just remove stdio.h from current patch, as it's not
>>> supposed to be provided in a freestanding environment.
>>
>> A huge number of files under tests/tcg/ have a #include <stdio.h>
>> currently.
> 
> They are all *-user mode tests though, which do need a proper libc.
> 
>>
>> In the example build failure in the commit message, we have
>>
>>    tests/tcg/s390x/system/../console.c
>>
>> which does
>>
>>    #include "../../../pc-bios/s390-ccw/sclp.c"
>>
>> and sclp.c has
>>
>>    #include "s390-ccw.h"
>>
>> and that header has:
>>
>>    #include <stdbool.h>
>>    #include <stddef.h>
>>    #include <stdint.h>
>>    #include <stdio.h>
>>
>> hence the 4 headers I added to the meson check.
>>
>> So AFAICT, our code is expecting stdio.h to be provided in a
>> -ffreestanding build. Have we got a more fundamental mistake
>> wrt our use of -ffreestanding, such that it is relying on
>> unintended functionality ?
> 
> They shouldn't - but s390x seems to be doing something funky here. Ilya
> can you explain what s390x is trying to do here?

s390x used to use SLOF headers before the meson rework.
I remember that Pierrick mentioned there were issues with checking out
the SLOF submodule, but it seems to work for me.
So I've posted my version of the fix [1], please take a look.

[1] 
https://lore.kernel.org/qemu-devel/20260914235113.272992-1-iii@linux.ibm.com/

> 
>>
>> With regards,
>> Daniel
>