x86/fpu/math-emu: Add support for FCMOVcc insns

Run-tested by booting with "no387 nofxsr" and running test
program:

  [RUN]   Testing fcmovCC instructions
  [OK]    fcmovCC

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Link: http://lkml.kernel.org/r/1442588010-20055-3-git-send-email-dvlasenk@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/math-emu/fpu_aux.c

@@ -169,6 +169,76 @@ void fxch_i(void)
 	fpu_tag_word = tag_word;
 }
 
+static void fcmovCC(void)
+{
+	/* fcmovCC st(i) */
+	int i = FPU_rm;
+	FPU_REG *st0_ptr = &st(0);
+	FPU_REG *sti_ptr = &st(i);
+	long tag_word = fpu_tag_word;
+	int regnr = top & 7;
+	int regnri = (top + i) & 7;
+	u_char sti_tag = (tag_word >> (regnri * 2)) & 3;
+
+	if (sti_tag == TAG_Empty) {
+		FPU_stack_underflow();
+		clear_C1();
+		return;
+	}
+	reg_copy(sti_ptr, st0_ptr);
+	tag_word &= ~(3 << (regnr * 2));
+	tag_word |= (sti_tag << (regnr * 2));
+	fpu_tag_word = tag_word;
+}
+
+void fcmovb(void)
+{
+	if (FPU_EFLAGS & X86_EFLAGS_CF)
+		fcmovCC();
+}
+
+void fcmove(void)
+{
+	if (FPU_EFLAGS & X86_EFLAGS_ZF)
+		fcmovCC();
+}
+
+void fcmovbe(void)
+{
+	if (FPU_EFLAGS & (X86_EFLAGS_CF|X86_EFLAGS_ZF))
+		fcmovCC();
+}
+
+void fcmovu(void)
+{
+	if (FPU_EFLAGS & X86_EFLAGS_PF)
+		fcmovCC();
+}
+
+void fcmovnb(void)
+{
+	if (!(FPU_EFLAGS & X86_EFLAGS_CF))
+		fcmovCC();
+}
+
+void fcmovne(void)
+{
+	if (!(FPU_EFLAGS & X86_EFLAGS_ZF))
+		fcmovCC();
+}
+
+void fcmovnbe(void)
+{
+	if (!(FPU_EFLAGS & (X86_EFLAGS_CF|X86_EFLAGS_ZF)))
+		fcmovCC();
+}
+
+void fcmovnu(void)
+{
+	if (!(FPU_EFLAGS & X86_EFLAGS_PF))
+		fcmovCC();
+}
+
 void ffree_(void)
 {
 	/* ffree st(i) */

arch/x86/math-emu/fpu_entry.c

@@ -40,7 +40,7 @@
 
 #define __BAD__ FPU_illegal	/* Illegal on an 80486, causes SIGILL */
 
-/* f(u)comi(p) are enabled if CPUID(1).EDX(15) "cmov" is set */
+/* fcmovCC and f(u)comi(p) are enabled if CPUID(1).EDX(15) "cmov" is set */
 
 /* WARNING: "u" entries are not documented by Intel in their 80486 manual
    and may not work on FPU clones or later Intel FPUs.
@@ -49,13 +49,13 @@
 static FUNC const st_instr_table[64] = {
 /* Opcode:	d8		d9		da		db */
 /*		dc		dd		de		df */
-/* c0..7 */	fadd__,		fld_i_,		__BAD__,	__BAD__,
+/* c0..7 */	fadd__,		fld_i_,		fcmovb,		fcmovnb,
 /* c0..7 */	fadd_i,		ffree_,		faddp_,		ffreep,/*u*/
-/* c8..f */	fmul__,		fxch_i,		__BAD__,	__BAD__,
+/* c8..f */	fmul__,		fxch_i,		fcmove,		fcmovne,
 /* c8..f */	fmul_i,		fxch_i,/*u*/	fmulp_,		fxch_i,/*u*/
-/* d0..7 */	fcom_st,	fp_nop,		__BAD__,	__BAD__,
+/* d0..7 */	fcom_st,	fp_nop,		fcmovbe,	fcmovnbe,
 /* d0..7 */	fcom_st,/*u*/	fst_i_,		fcompst,/*u*/	fstp_i,/*u*/
-/* d8..f */	fcompst,	fstp_i,/*u*/	__BAD__,	__BAD__,
+/* d8..f */	fcompst,	fstp_i,/*u*/	fcmovu,		fcmovnu,
 /* d8..f */	fcompst,/*u*/	fstp_i,		fcompp,		fstp_i,/*u*/
 /* e0..7 */	fsub__,		FPU_etc,	__BAD__,	finit_,
 /* e0..7 */	fsubri,		fucom_,		fsubrp,		fstsw_,
@@ -80,10 +80,10 @@ static FUNC const st_instr_table[64] = {
 
 static u_char const type_table[64] = {
 /* Opcode:	d8	d9	da	db	dc	dd	de	df */
-/* c0..7 */	_REGI_, _NONE_, _null_, _null_, _REGIi, _REGi_, _REGIp, _REGi_,
-/* c8..f */	_REGI_, _REGIn, _null_, _null_, _REGIi, _REGI_, _REGIp, _REGI_,
-/* d0..7 */	_REGIc, _NONE_, _null_, _null_, _REGIc, _REG0_, _REGIc, _REG0_,
-/* d8..f */	_REGIc, _REG0_, _null_, _null_, _REGIc, _REG0_, _REGIc, _REG0_,
+/* c0..7 */	_REGI_, _NONE_, _REGIn, _REGIn, _REGIi, _REGi_, _REGIp, _REGi_,
+/* c8..f */	_REGI_, _REGIn, _REGIn, _REGIn, _REGIi, _REGI_, _REGIp, _REGI_,
+/* d0..7 */	_REGIc, _NONE_, _REGIn, _REGIn, _REGIc, _REG0_, _REGIc, _REG0_,
+/* d8..f */	_REGIc, _REG0_, _REGIn, _REGIn, _REGIc, _REG0_, _REGIc, _REG0_,
 /* e0..7 */	_REGI_, _NONE_, _null_, _NONE_, _REGIi, _REGIc, _REGIp, _NONE_,
 /* e8..f */	_REGI_, _NONE_, _REGIc, _REGIc, _REGIi, _REGIc, _REGIp, _REGIc,
 /* f0..7 */	_REGI_, _NONE_, _null_, _REGIc, _REGIi, _null_, _REGIp, _REGIc,

arch/x86/math-emu/fpu_proto.h

@@ -46,6 +46,14 @@ extern void fstsw_(void);
 extern void fp_nop(void);
 extern void fld_i_(void);
 extern void fxch_i(void);
+extern void fcmovb(void);
+extern void fcmove(void);
+extern void fcmovbe(void);
+extern void fcmovu(void);
+extern void fcmovnb(void);
+extern void fcmovne(void);
+extern void fcmovnbe(void);
+extern void fcmovnu(void);
 extern void ffree_(void);
 extern void ffreep(void);
 extern void fst_i_(void);