Re: [RFC PATCH] configure: Poison (almost) all target-specific #defines

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 3/15/21 2:54 PM, Thomas Huth wrote:
> We are generating a lot of target-specific defines in the *-config-devices.h
> and *-config-target.h files. Using them in common code is wrong and leads
> to very subtle bugs since a "#ifdef CONFIG_SOMETHING" is not working there
> as expected. To avoid these issues, we are already poisoning some of the
> macros in include/exec/poison.h - but maintaining this list manually is
> cumbersome. Thus let's generate the list of poisoned macros automatically
> instead.
> Note that CONFIG_TCG (which is also defined in config-host.h) and

IIRC we can't poison CONFIG_XEN / CONFIG_HAX because they are
pulled in via "sysemu/hw_accel.h".

> CONFIG_USER_ONLY are special, so we have to filter these out.
> 
> Signed-off-by: Thomas Huth <thuth@redhat.com>
> ---
>  RFC since the shell stuff in "configure" is quite ugly ... maybe there's
>  a better way to do this via meson, but my meson-foo is still lacking...
> 
>  Makefile              | 2 +-
>  configure             | 5 +++++
>  include/exec/poison.h | 2 ++
>  3 files changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/Makefile b/Makefile
> index bcbbec71a1..4cab10a2a4 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -213,7 +213,7 @@ qemu-%.tar.bz2:
>  
>  distclean: clean
>  	-$(quiet-@)test -f build.ninja && $(NINJA) $(NINJAFLAGS) -t clean -g || :
> -	rm -f config-host.mak config-host.h*
> +	rm -f config-host.mak config-host.h* config-poison.h
>  	rm -f tests/tcg/config-*.mak
>  	rm -f config-all-disas.mak config.status
>  	rm -f roms/seabios/config.mak roms/vgabios/config.mak
> diff --git a/configure b/configure
> index f7d022a5db..c7b5df3a5c 100755
> --- a/configure
> +++ b/configure
> @@ -6441,6 +6441,11 @@ if test -n "${deprecated_features}"; then
>      echo "  features: ${deprecated_features}"
>  fi
>  
> +cat *-config-devices.h *-config-target.h | grep '^#define '  \
> +    | grep -v CONFIG_TCG | grep -v CONFIG_USER_ONLY \
> +    | sed -e 's/#define //' -e 's/ .*//' | sort -u \
> +    | sed -e 's/^/#pragma GCC poison /' > config-poison.h
> +
>  # Save the configure command line for later reuse.
>  cat <<EOD >config.status
>  #!/bin/sh
> diff --git a/include/exec/poison.h b/include/exec/poison.h
> index 4cd3f8abb4..9e55d5aec2 100644
> --- a/include/exec/poison.h
> +++ b/include/exec/poison.h
> @@ -4,6 +4,8 @@
>  #ifndef HW_POISON_H
>  #define HW_POISON_H
>  
> +#include "config-poison.h"
> +
>  #pragma GCC poison TARGET_I386
>  #pragma GCC poison TARGET_X86_64
>  #pragma GCC poison TARGET_AARCH64
>