[PATCH] x86: rework hypercall argument count table instantiation & use

[Jan Beulich <jbeulich@xxxxxxxx>]

The initial observation were duplicate symbols that our checking warns
about. Instead of merely renaming one or both pair(s) of symbols,
reduce #ifdef-ary at the same time by moving the instantiation of the
arrays into macros (a native and a 32-bit one each, where likely more
redundancy could be eliminated, if we really wanted to). While doing the
conversion also stop open-coding array_access_nospec().

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
A tentative variant with yet less redundancy (only a single macro
needed) would be

#define clobber_regs(r, n, t, b) ({ \
    static const unsigned char t ## b[] = hypercall_args_ ## t ## b; \
    clobber_regs ## b(r, array_access_nospec(t ## b, n)); \
})

with invocations then being e.g.

    clobber_regs(regs, eax, hvm, 64);

and with the clobber_regs() inline function renamed to clobber_regs64().

--- a/xen/arch/x86/hvm/hypercall.c
+++ b/xen/arch/x86/hvm/hypercall.c
@@ -111,11 +111,6 @@ long hvm_physdev_op(int cmd, XEN_GUEST_H
         return compat_physdev_op(cmd, arg);
 }
 
-#ifndef NDEBUG
-static const unsigned char hypercall_args_64[] = hypercall_args_hvm64;
-static const unsigned char hypercall_args_32[] = hypercall_args_hvm32;
-#endif
-
 int hvm_hypercall(struct cpu_user_regs *regs)
 {
     struct vcpu *curr = current;
@@ -177,7 +172,7 @@ int hvm_hypercall(struct cpu_user_regs *
                             regs->r10, regs->r8);
 
         if ( !curr->hcall_preempted && regs->rax != -ENOSYS )
-            clobber_regs(regs, get_nargs(hypercall_args_64, eax));
+            clobber_regs(regs, eax, hvm64);
     }
     else
     {
@@ -190,7 +185,7 @@ int hvm_hypercall(struct cpu_user_regs *
         curr->hcall_compat = false;
 
         if ( !curr->hcall_preempted && regs->eax != -ENOSYS )
-            clobber_regs32(regs, get_nargs(hypercall_args_32, eax));
+            clobber_regs32(regs, eax, hvm32);
     }
 
     hvmemul_cache_restore(curr, token);
--- a/xen/arch/x86/include/asm/hypercall.h
+++ b/xen/arch/x86/include/asm/hypercall.h
@@ -43,16 +43,6 @@ compat_common_vcpu_op(
 
 #endif /* CONFIG_COMPAT */
 
-#ifndef NDEBUG
-static inline unsigned int _get_nargs(const unsigned char *tbl, unsigned int c)
-{
-    return tbl[c];
-}
-#define get_nargs(t, c) _get_nargs(t, array_index_nospec(c, ARRAY_SIZE(t)))
-#else
-#define get_nargs(tbl, c) 0
-#endif
-
 static inline void clobber_regs(struct cpu_user_regs *regs,
                                 unsigned int nargs)
 {
@@ -69,6 +59,11 @@ static inline void clobber_regs(struct c
 #endif
 }
 
+#define clobber_regs(r, n, t) ({ \
+    static const unsigned char t[] = hypercall_args_ ## t; \
+    clobber_regs(r, array_access_nospec(t, n)); \
+})
+
 static inline void clobber_regs32(struct cpu_user_regs *regs,
                                   unsigned int nargs)
 {
@@ -85,4 +80,9 @@ static inline void clobber_regs32(struct
 #endif
 }
 
+#define clobber_regs32(r, n, t) ({ \
+    static const unsigned char t[] = hypercall_args_ ## t; \
+    clobber_regs32(r, array_access_nospec(t, n)); \
+})
+
 #endif /* __ASM_X86_HYPERCALL_H__ */
--- a/xen/arch/x86/pv/hypercall.c
+++ b/xen/arch/x86/pv/hypercall.c
@@ -27,13 +27,6 @@
 #include <asm/multicall.h>
 #include <irq_vectors.h>
 
-#ifndef NDEBUG
-static const unsigned char hypercall_args_64[] = hypercall_args_pv64;
-#ifdef CONFIG_PV32
-static const unsigned char hypercall_args_32[] = hypercall_args_pv32;
-#endif
-#endif
-
 /* Forced inline to cause 'compat' to be evaluated at compile time. */
 static void always_inline
 _pv_hypercall(struct cpu_user_regs *regs, bool compat)
@@ -65,7 +58,7 @@ _pv_hypercall(struct cpu_user_regs *regs
         call_handlers_pv64(eax, regs->rax, rdi, rsi, rdx, r10, r8);
 
         if ( !curr->hcall_preempted && regs->rax != -ENOSYS )
-            clobber_regs(regs, get_nargs(hypercall_args_64, eax));
+            clobber_regs(regs, eax, pv64);
     }
 #ifdef CONFIG_PV32
     else
@@ -90,7 +83,7 @@ _pv_hypercall(struct cpu_user_regs *regs
         curr->hcall_compat = false;
 
         if ( !curr->hcall_preempted && regs->eax != -ENOSYS )
-            clobber_regs32(regs, get_nargs(hypercall_args_32, eax));
+            clobber_regs32(regs, eax, pv32);
     }
 #endif /* CONFIG_PV32 */