[PULL 0/1] xen queue 2020-08-03

[PULL 0/1] xen queue 2020-08-03

[Anthony PERARD]

The following changes since commit 45a150aa2b3492acf6691c7bdbeb25a8545d8345:

  Merge remote-tracking branch 'remotes/ericb/tags/pull-bitmaps-2020-08-03' into staging (2020-08-03 15:13:49 +0100)

are available in the Git repository at:

  https://xenbits.xen.org/git-http/people/aperard/qemu-dm.git tags/pull-xen-20200803

for you to fetch changes up to b3fcc98f391e9a60a369d825333b852871cf67b0:

  accel/xen: Fix xen_enabled() behavior on target-agnostic objects (2020-08-03 17:39:38 +0100)

----------------------------------------------------------------
xen patches

bug fix

----------------------------------------------------------------
Philippe Mathieu-Daudé (1):
      accel/xen: Fix xen_enabled() behavior on target-agnostic objects

 include/sysemu/xen.h | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

[PULL 1/1] accel/xen: Fix xen_enabled() behavior on target-agnostic objects

[Anthony PERARD]

From: Philippe Mathieu-Daudé <philmd@redhat.com>

CONFIG_XEN is generated by configure and stored in "config-target.h",
which is (obviously) only include for target-specific objects.
This is a problem for target-agnostic objects as CONFIG_XEN is never
defined and xen_enabled() is always inlined as 'false'.

Fix by following the KVM schema, defining CONFIG_XEN_IS_POSSIBLE
when we don't know to force the call of the non-inlined function,
returning the xen_allowed boolean.

Fixes: da278d58a092 ("accel: Move Xen accelerator code under accel/xen/")
Reported-by: Paul Durrant <pdurrant@amazon.com>
Suggested-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Anthony PERARD <anthony.perard@citrix.com>
Tested-by: Paul Durrant <paul@xen.org>
Message-Id: <20200728100925.10454-1-philmd@redhat.com>
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
---
 include/sysemu/xen.h | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/include/sysemu/xen.h b/include/sysemu/xen.h
index 1ca292715e69..385a1fa2bff8 100644
--- a/include/sysemu/xen.h
+++ b/include/sysemu/xen.h
@@ -8,7 +8,15 @@
 #ifndef SYSEMU_XEN_H
 #define SYSEMU_XEN_H
 
-#ifdef CONFIG_XEN
+#ifdef NEED_CPU_H
+# ifdef CONFIG_XEN
+#  define CONFIG_XEN_IS_POSSIBLE
+# endif
+#else
+# define CONFIG_XEN_IS_POSSIBLE
+#endif
+
+#ifdef CONFIG_XEN_IS_POSSIBLE
 
 bool xen_enabled(void);
 
@@ -18,7 +26,7 @@ void xen_ram_alloc(ram_addr_t ram_addr, ram_addr_t size,
                    struct MemoryRegion *mr, Error **errp);
 #endif
 
-#else /* !CONFIG_XEN */
+#else /* !CONFIG_XEN_IS_POSSIBLE */
 
 #define xen_enabled() 0
 #ifndef CONFIG_USER_ONLY
@@ -33,6 +41,6 @@ static inline void xen_ram_alloc(ram_addr_t ram_addr, ram_addr_t size,
 }
 #endif
 
-#endif /* CONFIG_XEN */
+#endif /* CONFIG_XEN_IS_POSSIBLE */
 
 #endif
-- 
Anthony PERARD

Re: [PULL 0/1] xen queue 2020-08-03

[Peter Maydell]

On Mon, 3 Aug 2020 at 17:53, Anthony PERARD <anthony.perard@citrix.com> wrote:
> ----------------------------------------------------------------
> xen patches
>
> bug fix
>
> ----------------------------------------------------------------
> Philippe Mathieu-Daudé (1):
>       accel/xen: Fix xen_enabled() behavior on target-agnostic objects

This fails to compile, all hosts :-(

  LINK    avr-softmmu/qemu-system-avr
../migration/savevm.o: In function `qemu_loadvm_section_start_full':
/home/petmay01/linaro/qemu-for-merges/migration/savevm.c:2320:
undefined reference to `xen_enabled'
collect2: error: ld returned 1 exit status
[ditto other softmmu link attempts]

Similar but different on OSX:

  LINK    aarch64-softmmu/qemu-system-aarch64
Undefined symbols for architecture x86_64:
  "_xen_enabled", referenced from:
      _msix_is_masked in msix.o
      _msix_write_config in msix.o
      _msix_handle_mask_update in msix.o
      _msix_init in msix.o
      _msix_notify in msix.o
      _msix_reset in msix.o
      _msix_set_vector_notifiers in msix.o
      ...
ld: symbol(s) not found for architecture x86_64

Fails in all the BSD VM builds as well, so I don't think this
is related to incremental vs from-clean builds.

I think the failure here is only on builds where
CONFIG_XEN is not set by configure (which for my merge
build setup appears to be all of them, I think).
In that case when we build a target-agnostic object
it gets an external reference to the xen_enabled()
function, but because Xen is disabled we don't compile
accel/xen/ and so there is no actual implementation of
the function in the link.

This doesn't happen for KVM because there the
CONFIG_KVM_IS_POSSIBLE version of kvm_enabled()
is a #define:
#define kvm_enabled()           (kvm_allowed)
and we provide both the "real" version of the
'bool kvm_allowed' in accel/kvm/kvm-all.c and also
the stub version in accel/stubs/kvm-stub.c which will
be used in configurations thta don't build accel/kvm.

I think then that the fix for this build failure is to
either:
 (1) add a stub version of xen_allowed() to accel/stubs/xen-stub.c
     (which would always return false)

 (2) follow KVM more closely, and have xen_allowed() be
     a #define to (xen_allowed), with a (non-static)
     bool xen_allowed in accel/xen/xen-all.c and another
     one in accel/stubs/xen-stub.c

thanks
-- PMM