[Xen-devel] [PATCH for-4.13 1/6] xen/arm: fix get_cpu_info() when built with clang

[Julien Grall <julien.grall@xxxxxxx>]

Clang understands the GCCism in use here, but still complains that sp is
unitialised. In such cases, resort to the older versions of this code,
which directly read sp into the temporary variable.

Note that GCCism is still kept in default because other compilers (e.g.
clang) may also define __GNUC__, so AFAIK there are no proper way to
detect properly GCC.

This means that in the event Xen is ported to a new compiler, the code
will need to be updated. But that likely not going to be the only place
where Xen will need to be adapted...

This is based on the x86 counterpart.

Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
Acked-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>

---
    Changes in v2:
        - Update the commit message to explain the ordering in the code.
        - Add Stefano's acked-by
---
 xen/include/asm-arm/current.h | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/xen/include/asm-arm/current.h b/xen/include/asm-arm/current.h
index 1653e89d30..80503578cf 100644
--- a/xen/include/asm-arm/current.h
+++ b/xen/include/asm-arm/current.h
@@ -28,8 +28,16 @@ struct cpu_info {
 
 static inline struct cpu_info *get_cpu_info(void)
 {
+#ifdef __clang__
+    unsigned long sp;
+
+    asm ("mov %0, sp" : "=r" (sp));
+#else
     register unsigned long sp asm ("sp");
-    return (struct cpu_info *)((sp & ~(STACK_SIZE - 1)) + STACK_SIZE - 
sizeof(struct cpu_info));
+#endif
+
+    return (struct cpu_info *)((sp & ~(STACK_SIZE - 1)) +
+                               STACK_SIZE - sizeof(struct cpu_info));
 }
 
 #define guest_cpu_user_regs() (&get_cpu_info()->guest_cpu_user_regs)
-- 
2.11.0


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