[PATCH] D76096: [clang] allow const structs/unions/arrays to be constant expressions for C

[Nathan Chancellor via Phabricator via cfe-commits]

nathanchance added a comment.

In D76096#4564855 <https://reviews.llvm.org/D76096#4564855>, @DavidSpickett wrote:

> One of the kernel tests now fails to build for AArch64 and Arm:
>
>   00:00:48 ++ make CC=/home/tcwg-buildslave/workspace/tcwg_kernel_0/bin/aarch64-cc LD=/home/tcwg-buildslave/workspace/tcwg_kernel_0/llvm-install/bin/ld.lld SUBLEVEL=0 EXTRAVERSION=-bisect ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- HOSTCC=/home/tcwg-buildslave/workspace/tcwg_kernel_0/llvm-install/bin/clang -j32 -s -k
>   00:08:26 lib/test_scanf.c:661:2: error: implicit conversion from 'int' to 'unsigned char' changes value from -168 to 88 [-Werror,-Wconstant-conversion]
>   00:08:26   661 |         test_number_prefix(unsigned char,       "0xA7", "%2hhx%hhx", 0, 0xa7, 2, check_uchar);
>   00:08:26       |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>   00:08:26 lib/test_scanf.c:609:29: note: expanded from macro 'test_number_prefix'
>   00:08:26   609 |         T result[2] = {~expect[0], ~expect[1]};                                 \
>   00:08:26       |                       ~            ^~~~~~~~~~
>   00:08:27 1 error generated.
>   00:08:27 make[3]: *** [scripts/Makefile.build:243: lib/test_scanf.o] Error 1
>
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/lib/test_scanf.c#n661
>
> Seems like the test should be fixed, though I wonder why this same error isn't effecting GCC builds.

Thanks for the report! I sent a patch for this already, just waiting for it to be picked up: https://lore.kernel.org/20230807-test_scanf-wconstant-conversion-v2-1-839ca39083e1@kernel.org/


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