[PATCH v3 07/11] arm: use r12 to pass the hypercall number

[Stefano Stabellini <stefano.stabellini@eu.citrix.com>]

Use r12 to pass the hypercall number and r0-r4 for the hypercall
arguments.

Use the ISS to pass an hypervisor specific tag.

Remove passing unused registers to arm_hypercall_table: we don't have 6
arguments hypercalls and we never use 64 bit values as hypercall
arguments, 64 bit values are only contained within structs passed as
arguments.


Changes in v3:

- move XEN_HYPERCALL_TAG to a public header;

- clobber register in the debug build;

- document calling convention;

- check if arm_hypercall_table[regs->r12] != NULL.


Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
---
 xen/arch/arm/traps.c          |   31 ++++++++++++++++++++-----------
 xen/include/public/arch-arm.h |   21 +++++++++++++++++++++
 2 files changed, 41 insertions(+), 11 deletions(-)

diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
index 395d0af..750f85a 100644
--- a/xen/arch/arm/traps.c
+++ b/xen/arch/arm/traps.c
@@ -367,7 +367,6 @@ unsigned long do_arch_0(unsigned int cmd, unsigned long long value)
 }
 
 typedef unsigned long arm_hypercall_t(
-    unsigned int, unsigned int, unsigned int, unsigned int, unsigned int,
     unsigned int, unsigned int, unsigned int, unsigned int, unsigned int);
 
 #define HYPERCALL(x)                                        \
@@ -407,18 +406,28 @@ static void do_debug_trap(struct cpu_user_regs *regs, unsigned int code)
 
 static void do_trap_hypercall(struct cpu_user_regs *regs, unsigned long iss)
 {
+    arm_hypercall_t *call = NULL;
     local_irq_enable();
 
-    regs->r0 = arm_hypercall_table[iss](regs->r0,
-                             regs->r1,
-                             regs->r2,
-                             regs->r3,
-                             regs->r4,
-                             regs->r5,
-                             regs->r6,
-                             regs->r7,
-                             regs->r8,
-                             regs->r9);
+    if ( iss != XEN_HYPERCALL_TAG  ) {
+        printk("%s %d: received an alien hypercall iss=%lx\n", __func__ ,
+                __LINE__ , iss);
+        regs->r0 = -EINVAL;
+        return;
+    }
+
+    call = arm_hypercall_table[regs->r12];
+    if ( call == NULL ) {
+        regs->r0 = -ENOSYS;
+        return;
+    }
+
+    regs->r0 = call(regs->r0, regs->r1, regs->r2, regs->r3, regs->r4);
+
+#ifdef DEBUG
+    /* clobber registers */
+    regs->r1 = regs->r2 = regs->r3 = regs->r4 = regs->r12 = 0xDEADBEEF;
+#endif
 }
 
 static void do_cp15_32(struct cpu_user_regs *regs,
diff --git a/xen/include/public/arch-arm.h b/xen/include/public/arch-arm.h
index e3d5c08..4f16bde 100644
--- a/xen/include/public/arch-arm.h
+++ b/xen/include/public/arch-arm.h
@@ -27,6 +27,27 @@
 #ifndef __XEN_PUBLIC_ARCH_ARM_H__
 #define __XEN_PUBLIC_ARCH_ARM_H__
 
+/* hypercall calling convention
+ * ----------------------------
+ *
+ * An hypercall is issued using the ARM HVC instruction.
+ *
+ * The hypercall arguments go on the registers, the first argument on
+ * r0, the second argument on r1, the third on r2, and so on.
+ *
+ * The hypercall number is passed on r12.
+ *
+ * The HVC ISS must contain a Xen specific TAG: XEN_HYPERCALL_TAG.
+ *
+ * The return value is passed on r0.
+ *
+ * The hypercall will clobber r0, r1, r2, r3, r4 and r12.
+ *
+ */
+
+#define XEN_HYPERCALL_TAG   0XEA1
+
+
 #ifndef __ASSEMBLY__
 #define ___DEFINE_XEN_GUEST_HANDLE(name, type) \
     typedef struct { type *p; } __guest_handle_ ## name
-- 
1.7.2.5