[PATCH for_v23 4/5] x86/vdso: sgx: Reorder params to callback to improve readability

[Sean Christopherson <sean.j.christopherson@intel.com>]

Swap @ret and @ursp in the callback prototype so that the output from
the vDSO itself, @ret and @e, are grouped together.  Having the first
N parameters all share a type also makes the prototype easier to parse
by (some) humans.  And, passing @ursp via register saves one whole
MOV instruction!

Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---
 arch/x86/entry/vdso/vsgx_enter_enclave.S | 16 +++++++---------
 arch/x86/include/uapi/asm/sgx.h          | 10 +++++-----
 2 files changed, 12 insertions(+), 14 deletions(-)

diff --git a/arch/x86/entry/vdso/vsgx_enter_enclave.S b/arch/x86/entry/vdso/vsgx_enter_enclave.S
index 3dd22780b7ef..94f613b53b13 100644
--- a/arch/x86/entry/vdso/vsgx_enter_enclave.S
+++ b/arch/x86/entry/vdso/vsgx_enter_enclave.S
@@ -134,23 +134,21 @@ ENTRY(__vdso_sgx_enter_enclave)
 	jmp	.Lhandle_exit
 
 .Linvoke_userspace_handler:
+	/* Pass the untrusted RSP (at exit) to the callback via %rcx. */
+	mov	%rsp, %rcx
+
 	/*
-	 * Align stack per x86_64 ABI. Save the original %rsp in %rbx to be
-	 * restored after the callback returns.  Note, %rsp needs to be 16-byte
-	 * aligned _after_ pushing the three parameters on the stack.
+	 * Align stack per x86_64 ABI. Note, %rsp needs to be 16-byte aligned
+	 * _after_ pushing the three parameters on the stack.
 	 */
-	mov	%rsp, %rbx
 	and	$-0x10, %rsp
 	sub	$0x8, %rsp
 
-	/* Push @e, u_rsp and @tcs as parameters to the callback. */
+	/* Push @e, the "return" value and @tcs as params to the callback. */
 	push	0x18(%rbp)
-	push	%rbx
+	push	%rax
 	push	0x10(%rbp)
 
-	/* Pass the "return" value to the callback via %rcx. */
-	mov	%eax, %ecx
-
 	/* Clear RFLAGS.DF per x86_64 ABI */
 	cld
 
diff --git a/arch/x86/include/uapi/asm/sgx.h b/arch/x86/include/uapi/asm/sgx.h
index 255392f5054f..95f69f938b58 100644
--- a/arch/x86/include/uapi/asm/sgx.h
+++ b/arch/x86/include/uapi/asm/sgx.h
@@ -88,16 +88,16 @@ struct sgx_enclave_exception {
  * @rdi:	RDI at the time of enclave exit
  * @rsi:	RSI at the time of enclave exit
  * @rdx:	RDX at the time of enclave exit
- * @ret:	0 on success (EEXIT), -EFAULT on an exception
+ * @ursp:	RSP at the time of enclave exit (untrusted stack)
  * @r8:		R8 at the time of enclave exit
  * @r9:		R9 at the time of enclave exit
  * @tcs:	Thread Control Structure used to enter enclave
- * @ursp:	RSP at the time of enclave exit
+ * @ret:	0 on success (EEXIT), -EFAULT on an exception
  * @e:		Pointer to struct sgx_enclave_exception (as provided by caller)
  */
-typedef int (*sgx_enclave_exit_handler_t)(long rdi, long rsi, long rdx, int ret,
-					  long r8, long r9, void *tcs,
-					  long ursp,
+typedef int (*sgx_enclave_exit_handler_t)(long rdi, long rsi, long rdx,
+					  long ursp, long r8, long r9,
+					  void *tcs, int ret,
 					  struct sgx_enclave_exception *e);
 
 #endif /* _UAPI_ASM_X86_SGX_H */
-- 
2.22.0