[PATCH v2 26/30] build: Disable weak symbols for MSYS2

[Bin Meng]

Hi Simon,

On Sun, Apr 30, 2023 at 9:30 AM Simon Glass <sjg at chromium.org> wrote:
>
> Weak symbols are not well supported by the PE format, so disable them.
> We need to manually ensure that only one function is present in the source
> code.
>
> Add a Kconfig option to control this and enable it when building for
> Windows.
>
> Signed-off-by: Simon Glass <sjg at chromium.org>
> ---
>
> (no changes since v1)
>
>  Kconfig                             | 12 ++++++++++++
>  include/linux/compiler_attributes.h |  4 ++++
>  2 files changed, 16 insertions(+)
>
> diff --git a/Kconfig b/Kconfig
> index 9ac816abef1c..985b09680934 100644
> --- a/Kconfig
> +++ b/Kconfig
> @@ -75,6 +75,18 @@ config CLANG_VERSION
>  config CC_IS_MSYS
>         def_bool $(success,uname -o | grep -q Msys)
>
> +config WEAK_SYMBOLS
> +       bool "Enable use of weak symbols"
> +       default y if !CC_IS_MSYS
> +       help
> +         The Portable Executable (PE) format used by Windows does not support
> +         weak symbols very well. Even where it can be made to work, the __weak
> +         function attribute cannot be made to work with PE. Supporting weak
> +         symbols would involve changing the source code in undesirable ways.
> +
> +         This option controls whether weak symbols are used, or not. When
> +         disabled, the __weak function attribute does nothing.
> +
>  choice
>         prompt "Optimization level"
>         default CC_OPTIMIZE_FOR_SIZE
> diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h
> index 44c9a08d7346..c954109a065b 100644
> --- a/include/linux/compiler_attributes.h
> +++ b/include/linux/compiler_attributes.h
> @@ -268,6 +268,10 @@
>   *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html#index-weak-function-attribute
>   *   gcc: https://gcc.gnu.org/onlinedocs/gcc/Common-Variable-Attributes.html#index-weak-variable-attribute
>   */
> +#ifdef CONFIG_WEAK_SYMBOLS
>  #define __weak                          __attribute__((__weak__))
> +#else
> +#define __weak
> +#endif
>
>  #endif /* __LINUX_COMPILER_ATTRIBUTES_H */
> --

I am adding Fangrui who is a toolchain expert to this thread.

I chatted with him off-line, he thought we could probably go with the
GCC+lld-link route. GNU ld's PE/COFF support is quite out of date.

Maybe switching to lld-link could also solve the linker script issue
you are trying to resolve in patch#23 "sandbox: Augment the linker
script for MSYS2" ?

Regards,
Bin