[PATCH 2/2] x86/asm/entry/64: Clean up usage of TEST insns

[Denys Vlasenko]

By the nature of TEST operation, it is often possible
to test a narrower part of the operand:

    "testl $3, mem"  -> "testb $3, mem"

This results in shorter insns, because TEST insn has no
sign-entending byte-immediate forms unlike other ALU ops.

   text	   data	    bss	    dec	    hex	filename
  11674	      0	      0	  11674	   2d9a	entry_64.o.before
  11658	      0	      0	  11658	   2d8a	entry_64.o

Changes in object code:

-	f7 84 24 88 00 00 00 03 00 00 00 	testl  $0x3,0x88(%rsp)
+	f6 84 24 88 00 00 00 03	         	testb  $0x3,0x88(%rsp)
-	f7 44 24 68 03 00 00 00          	testl  $0x3,0x68(%rsp)
+	f6 44 24 68 03                  	testb  $0x3,0x68(%rsp)
-	f7 84 24 90 00 00 00 03 00 00 00	testl  $0x3,0x90(%rsp)
+	f6 84 24 90 00 00 00 03         	testb  $0x3,0x90(%rsp)

Signed-off-by: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
CC: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
CC: Steven Rostedt <rostedt@xxxxxxxxxxx>
CC: Ingo Molnar <mingo@xxxxxxxxxx>
CC: Borislav Petkov <bp@xxxxxxxxx>
CC: "H. Peter Anvin" <hpa@xxxxxxxxx>
CC: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
CC: Oleg Nesterov <oleg@xxxxxxxxxx>
CC: Frederic Weisbecker <fweisbec@xxxxxxxxx>
CC: Alexei Starovoitov <ast@xxxxxxxxxxxx>
CC: Will Drewry <wad@xxxxxxxxxxxx>
CC: Kees Cook <keescook@xxxxxxxxxxxx>
CC: x86@xxxxxxxxxx
CC: linux-kernel@xxxxxxxxxxxxxxx
---
 arch/x86/kernel/entry_64.S | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 8f8b22a..60705b03 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -601,7 +601,7 @@ ENTRY(ret_from_fork)
 
 	RESTORE_EXTRA_REGS
 
-	testl $3,CS(%rsp)			# from kernel_thread?
+	testb	$3, CS(%rsp)			# from kernel_thread?
 
 	/*
 	 * By the time we get here, we have no idea whether our pt_regs,
@@ -665,7 +665,7 @@ END(irq_entries_start)
 
 	leaq -RBP(%rsp),%rdi	/* arg1 for \func (pointer to pt_regs) */
 
-	testl $3, CS-RBP(%rsp)
+	testb	$3, CS-RBP(%rsp)
 	jz	1f
 	SWAPGS
 1:
@@ -720,7 +720,7 @@ ret_from_intr:
 	CFI_DEF_CFA_REGISTER	rsp
 	CFI_ADJUST_CFA_OFFSET	RBP
 
-	testl $3,CS(%rsp)
+	testb	$3, CS(%rsp)
 	jz	retint_kernel
 	/* Interrupt came from user space */
 
@@ -968,7 +968,7 @@ ENTRY(\sym)
 	.if \paranoid
 	.if \paranoid == 1
 	CFI_REMEMBER_STATE
-	testl $3, CS(%rsp)		/* If coming from userspace, switch */
+	testb	$3, CS(%rsp)		/* If coming from userspace, switch */
 	jnz 1f				/* stacks. */
 	.endif
 	call paranoid_entry
@@ -1309,7 +1309,7 @@ ENTRY(error_entry)
 	SAVE_C_REGS 8
 	SAVE_EXTRA_REGS 8
 	xorl %ebx,%ebx
-	testl $3,CS+8(%rsp)
+	testb	$3, CS+8(%rsp)
 	jz	error_kernelspace
 error_swapgs:
 	SWAPGS
@@ -1606,7 +1606,6 @@ end_repeat_nmi:
 	je 1f
 	movq %r12, %cr2
 1:
-	
 	testl %ebx,%ebx				/* swapgs needed? */
 	jnz nmi_restore
 nmi_swapgs:
-- 
1.8.1.4

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