On Fri, 2020-02-14 at 20:33 +0100, Paolo Bonzini wrote:
> On 14/02/20 20:14, Qian Cai wrote:
> > > It seems misguided to define a local variable just to get an implicit
> > > cast from (void *) to (fastop_t). Sean's first suggestion gives you
> > > the same implicit cast without the local variable. The second
> > > suggestion makes both casts explicit.
> >
> > OK, I'll do a v2 using the first suggestion which looks simpler once it passed
> > compilations.
> >
>
> Another interesting possibility is to use an unnamed union of a
> (*execute) function pointer and a (*fastop) function pointer.
>
This?
diff --git a/arch/x86/include/asm/kvm_emulate.h
b/arch/x86/include/asm/kvm_emulate.h
index 03946eb3e2b9..2a8f2bd2e5cf 100644
--- a/arch/x86/include/asm/kvm_emulate.h
+++ b/arch/x86/include/asm/kvm_emulate.h
@@ -292,6 +292,14 @@ enum x86emul_mode {
#define X86EMUL_SMM_MASK (1 << 6)
#define X86EMUL_SMM_INSIDE_NMI_MASK (1 << 7)
+/*
+ * fastop functions are declared as taking a never-defined fastop parameter,
+ * so they can't be called from C directly.
+ */
+struct fastop;
+
+typedef void (*fastop_t)(struct fastop *);
+
struct x86_emulate_ctxt {
const struct x86_emulate_ops *ops;
@@ -324,7 +332,10 @@ struct x86_emulate_ctxt {
struct operand src;
struct operand src2;
struct operand dst;
- int (*execute)(struct x86_emulate_ctxt *ctxt);
+ union {
+ int (*execute)(struct x86_emulate_ctxt *ctxt);
+ fastop_t fop;
+ };
int (*check_perm)(struct x86_emulate_ctxt *ctxt);
/*
* The following six fields are cleared together,
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index ddbc61984227..dd19fb3539e0 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -191,25 +191,6 @@
#define NR_FASTOP (ilog2(sizeof(ulong)) + 1)
#define FASTOP_SIZE 8
-/*
- * fastop functions have a special calling convention:
- *
- * dst: rax (in/out)
- * src: rdx (in/out)
- * src2: rcx (in)
- * flags: rflags (in/out)
- * ex: rsi (in:fastop pointer, out:zero if exception)
- *
- * Moreover, they are all exactly FASTOP_SIZE bytes long, so functions for
- * different operand sizes can be reached by calculation, rather than a jump
- * table (which would be bigger than the code).
- *
- * fastop functions are declared as taking a never-defined fastop parameter,
- * so they can't be called from C directly.
- */
-
-struct fastop;
-
struct opcode {
u64 flags : 56;
u64 intercept : 8;
@@ -311,8 +292,19 @@ static void invalidate_registers(struct x86_emulate_ctxt
*ctxt)
#define ON64(x)
#endif
-typedef void (*fastop_t)(struct fastop *);
-
+/*
+ * fastop functions have a special calling convention:
+ *
+ * dst: rax (in/out)
+ * src: rdx (in/out)
+ * src2: rcx (in)
+ * flags: rflags (in/out)
+ * ex: rsi (in:fastop pointer, out:zero if exception)
+ *
+ * Moreover, they are all exactly FASTOP_SIZE bytes long, so functions for
+ * different operand sizes can be reached by calculation, rather than a jump
+ * table (which would be bigger than the code).
+ */
static int fastop(struct x86_emulate_ctxt *ctxt, fastop_t fop);
#define __FOP_FUNC(name) \
@@ -5683,7 +5675,7 @@ int x86_emulate_insn(struct x86_emulate_ctxt *ctxt)
if (ctxt->execute) {
if (ctxt->d & Fastop)
- rc = fastop(ctxt, (fastop_t)ctxt->execute);
+ rc = fastop(ctxt, ctxt->fop);
else
rc = ctxt->execute(ctxt);
if (rc != X86EMUL_CONTINUE)
