[04/16] compiler.h: add QEMU_{BEGIN, END}_IGNORE_INITIALIZER_OVERRIDES

Commit Message

Marc-André Lureau May 4, 2022, 5:30 p.m. UTC

From: Marc-André Lureau <[e-mail]>

clang has this default warning which QEMU codes triggers in many
situations. However, other projects in general may not want to disable
globally the warning but only in limited specific code blocks.

Signed-off-by: Marc-André Lureau <[e-mail]>
---
 include/qemu/compiler.h | 11 +++++++++++
 1 file changed, 11 insertions(+)

Comments

Peter Maydell May 4, 2022, 6:41 p.m. UTC | #1

On Wed, 4 May 2022 at 18:36, <[e-mail]> wrote:
>
> From: Marc-André Lureau <[e-mail]>
>
> clang has this default warning which QEMU codes triggers in many
> situations. However, other projects in general may not want to disable
> globally the warning but only in limited specific code blocks.
>
> Signed-off-by: Marc-André Lureau <[e-mail]>

> +#if defined (__clang__)
> +#define QEMU_BEGIN_IGNORE_INITIALIZER_OVERRIDES                     \
> +    _Pragma("clang diagnostic push")                                \
> +    _Pragma("clang diagnostic ignored \"-Winitializer-overrides\"")
> +#define QEMU_END_IGNORE_INITIALIZER_OVERRIDES \
> +    _Pragma("clang diagnostic pop")
> +#else
> +#define QEMU_BEGIN_IGNORE_INITIALIZER_OVERRIDES
> +#define QEMU_END_IGNORE_INITIALIZER_OVERRIDES
> +#endif

We use pragma diagnostic controls generally sparingly and
only when we need to briefly disable an otherwise widely
useful warning. In this case the clang warning is just
broken (because it doesn't correctly handle the array
range initializer extension we use), and so we turn off
the warning altogether in configure, so that we get the
behaviour we want everywhere in the source tree, not just
if we mark it up with special macros.

If other projects want to borrow bits of QEMU code then
they need to either (a) abide by our conventions for
what compiler warnings to enable or disable, or else
(b) fork the code and fiddle with their own copy.

I don't really want to see QEMU's source code get littered
with a pile of extra macros hiding diagnostic pragmas.
(If we stop passing -Wno-initializer-overrides to the
compiler then we set a bunch of new "built on gcc on the
developer's machine but fails to build on clang in the
CI jobs" traps for ourselves, and if we don't stop passing
that then the places that should be marked up with the
macros won't reliably be marked up.)

thanks
-- PMM

Paolo Bonzini May 5, 2022, 6:55 a.m. UTC | #2

>If other projects want to borrow bits of QEMU code then
>they need to either (a) abide by our conventions for
>what compiler warnings to enable or disable, or else
>(b) fork the code and fiddle with their own copy.

Agreed, it's not a huge deal if a single add_project_arguments call is duplicated across a couple meson subprojects.

Paolo

>
>I don't really want to see QEMU's source code get littered
>with a pile of extra macros hiding diagnostic pragmas.
>(If we stop passing -Wno-initializer-overrides to the
>compiler then we set a bunch of new "built on gcc on the
>developer's machine but fails to build on clang in the
>CI jobs" traps for ourselves, and if we don't stop passing
>that then the places that should be marked up with the
>macros won't reliably be marked up.)
>
>thanks
>-- PMM
>

Patch

diff --git a/include/qemu/compiler.h b/include/qemu/compiler.h
index f20a76e4a286..ea0797959641 100644
--- a/include/qemu/compiler.h
+++ b/include/qemu/compiler.h
@@ -184,4 +184,15 @@ 
 #define QEMU_DISABLE_CFI
 #endif
 
+#if defined (__clang__)
+#define QEMU_BEGIN_IGNORE_INITIALIZER_OVERRIDES                     \
+    _Pragma("clang diagnostic push")                                \
+    _Pragma("clang diagnostic ignored \"-Winitializer-overrides\"")
+#define QEMU_END_IGNORE_INITIALIZER_OVERRIDES \
+    _Pragma("clang diagnostic pop")
+#else
+#define QEMU_BEGIN_IGNORE_INITIALIZER_OVERRIDES
+#define QEMU_END_IGNORE_INITIALIZER_OVERRIDES
+#endif
+
 #endif /* COMPILER_H */