The variable $(CFLAGS) is too often set in the environment,
especially when building a package for a distribution. Often, those
CFLAGS are intended to be use to build user spaces binaries, not a
kernel. This mean packager needs to takes extra steps to build Xen by
overriding the CFLAGS provided by the package build environment.

With this patch, we avoid using the variable $(CFLAGS). Also, the
hypervisor's build system have complete control over which CFLAGS are
used.

No change intended to XEN_CFLAGS used, beside some flags which may be
in a different order on the command line.

Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
---

Notes:
    There's still $(EXTRA_CFLAGS_XEN_CORE) which allows to add more CFLAGS
    if someone building Xen needs to add more CFLAGS to the hypervisor
    build.

 xen/Makefile         | 11 ++++++++++-
 xen/arch/arm/arch.mk |  4 ++++
 xen/arch/x86/arch.mk |  2 ++
 3 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/xen/Makefile b/xen/Makefile
index b3bffe8c6f..4dc3acf2a6 100644
--- a/xen/Makefile
+++ b/xen/Makefile
@@ -259,7 +259,16 @@ export KBUILD_DEFCONFIG := $(ARCH)_defconfig
 export XEN_TREEWIDE_CFLAGS := $(CFLAGS)
 
 XEN_AFLAGS =
-XEN_CFLAGS = $(CFLAGS)
+XEN_CFLAGS =
+ifeq ($(XEN_OS),SunOS)
+    XEN_CFLAGS +=  -Wa,--divide -D_POSIX_C_SOURCE=200112L -D__EXTENSIONS__
+endif
+XEN_CFLAGS += -fno-strict-aliasing
+XEN_CFLAGS += -std=gnu99
+XEN_CFLAGS += -Wall -Wstrict-prototypes
+$(call cc-option-add,XEN_CFLAGS,CC,-Wdeclaration-after-statement)
+$(call cc-option-add,XEN_CFLAGS,CC,-Wno-unused-but-set-variable)
+$(call cc-option-add,XEN_CFLAGS,CC,-Wno-unused-local-typedefs)
 
 # CLANG_FLAGS needs to be calculated before calling Kconfig
 ifneq ($(shell $(CC) --version 2>&1 | head -n 1 | grep clang),)
diff --git a/xen/arch/arm/arch.mk b/xen/arch/arm/arch.mk
index 300b8bf7ae..0478fadde2 100644
--- a/xen/arch/arm/arch.mk
+++ b/xen/arch/arm/arch.mk
@@ -1,6 +1,10 @@
 ########################################
 # arm-specific definitions
 
+ifeq ($(XEN_TARGET_ARCH),arm32)
+    XEN_CFLAGS += -marm
+endif
+
 $(call cc-options-add,XEN_CFLAGS,CC,$(EMBEDDED_EXTRA_CFLAGS))
 $(call cc-option-add,XEN_CFLAGS,CC,-Wnested-externs)
 
diff --git a/xen/arch/x86/arch.mk b/xen/arch/x86/arch.mk
index 5df3cf6bc3..fc3b1dc922 100644
--- a/xen/arch/x86/arch.mk
+++ b/xen/arch/x86/arch.mk
@@ -1,6 +1,8 @@
 ########################################
 # x86-specific definitions
 
+XEN_CFLAGS += -m64
+
 export XEN_IMG_OFFSET := 0x200000
 
 XEN_CFLAGS += -I$(srctree)/arch/x86/include/asm/mach-generic
-- 
Anthony PERARD

On 23.05.2023 18:38, Anthony PERARD wrote:
> The variable $(CFLAGS) is too often set in the environment,
> especially when building a package for a distribution. Often, those
> CFLAGS are intended to be use to build user spaces binaries, not a
> kernel. This mean packager needs to takes extra steps to build Xen by
> overriding the CFLAGS provided by the package build environment.
> 
> With this patch, we avoid using the variable $(CFLAGS). Also, the
> hypervisor's build system have complete control over which CFLAGS are
> used.

"..., apart from $(EXTRA_CFLAGS_XEN_CORE)", as you say ...

> No change intended to XEN_CFLAGS used, beside some flags which may be
> in a different order on the command line.
> 
> Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
> ---
> 
> Notes:
>     There's still $(EXTRA_CFLAGS_XEN_CORE) which allows to add more CFLAGS
>     if someone building Xen needs to add more CFLAGS to the hypervisor
>     build.

... only here.

> --- a/xen/Makefile
> +++ b/xen/Makefile
> @@ -259,7 +259,16 @@ export KBUILD_DEFCONFIG := $(ARCH)_defconfig
>  export XEN_TREEWIDE_CFLAGS := $(CFLAGS)
>  
>  XEN_AFLAGS =
> -XEN_CFLAGS = $(CFLAGS)
> +XEN_CFLAGS =
> +ifeq ($(XEN_OS),SunOS)
> +    XEN_CFLAGS +=  -Wa,--divide -D_POSIX_C_SOURCE=200112L -D__EXTENSIONS__

So this (and the arch.mk additions) duplicate stuff we have in config/*.mk.
Such duplication isn't really nice. Setting AS, CC, etc also happens there,
and hence I expect you're going to duplicate that as well in a later patch.
Can't we massage (if necessary) the config/*.mk relevant to the hypervisor
build, so they can be included from xen/Makefile? That way all such basic
settings could remain in a central place, which has been well known for
many years.

Jan

> On 23 May 2023, at 17:38, Anthony PERARD <anthony.perard@citrix.com> wrote:
> 
> The variable $(CFLAGS) is too often set in the environment,
> especially when building a package for a distribution. Often, those
> CFLAGS are intended to be use to build user spaces binaries, not a

NIT: s/use/used/

But I’m not a native speaker so I might be wrong on this

> kernel. This mean packager needs to takes extra steps to build Xen by
> overriding the CFLAGS provided by the package build environment.
> 
> With this patch, we avoid using the variable $(CFLAGS). Also, the
> hypervisor's build system have complete control over which CFLAGS are
> used.
> 
> No change intended to XEN_CFLAGS used, beside some flags which may be
> in a different order on the command line.
> 
> Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
> ---
> 
> Notes:
>    There's still $(EXTRA_CFLAGS_XEN_CORE) which allows to add more CFLAGS
>    if someone building Xen needs to add more CFLAGS to the hypervisor
>    build.
> 

Reviewed-by: Luca Fancellu <luca.fancellu@arm.com>
Tested-by: Luca Fancellu <luca.fancellu@arm.com>