runtime: check and fail early with a message if MMX is not available on 386

Fixes #12970.

Change-Id: Id0026e8274e071d65d47df63d65a93110abbec5d
Reviewed-on: https://go-review.googlesource.com/15998
Reviewed-by: Keith Randall <[email protected]>
Run-TryBot: Brad Fitzpatrick <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>

Author: minux

src/runtime/asm_386.s

@@ -26,6 +26,32 @@ TEXT runtime·rt0_go(SB),NOSPLIT,$0
 	MOVL	SP, (g_stack+stack_hi)(BP)
 
 	// find out information about the processor we're on
+#ifdef GOOS_nacl // NaCl doesn't like PUSHFL/POPFL
+	JMP 	has_cpuid
+#else
+	// first see if CPUID instruction is supported.
+	PUSHFL
+	PUSHFL
+	XORL	$(1<<21), 0(SP) // flip ID bit
+	POPFL
+	PUSHFL
+	POPL	AX
+	XORL	0(SP), AX
+	POPFL	// restore EFLAGS
+	TESTL	$(1<<21), AX
+	JNE 	has_cpuid
+#endif
+
+bad_proc: // show that the program requires MMX.
+	MOVL	$2, 0(SP)
+	MOVL	$bad_proc_msg<>(SB), 4(SP)
+	MOVL	$0x3d, 8(SP)
+	CALL	runtime·write(SB)
+	MOVL	$1, 0(SP)
+	CALL	runtime·exit(SB)
+	INT	$3
+
+has_cpuid:
 	MOVL	$0, AX
 	CPUID
 	CMPL	AX, $0
@@ -48,6 +74,11 @@ notintel:
 	MOVL	CX, AX // Move to global variable clobbers CX when generating PIC
 	MOVL	AX, runtime·cpuid_ecx(SB)
 	MOVL	DX, runtime·cpuid_edx(SB)
+
+	// Check for MMX support
+	TESTL	$(1<<23), DX	// MMX
+	JZ 	bad_proc
+
 nocpuinfo:	
 
 	// if there is an _cgo_init, call it to let it
@@ -129,6 +160,17 @@ ok:
 	INT $3
 	RET
 
+DATA	bad_proc_msg<>+0x00(SB)/8, $"This pro"
+DATA	bad_proc_msg<>+0x08(SB)/8, $"gram can"
+DATA	bad_proc_msg<>+0x10(SB)/8, $" only be"
+DATA	bad_proc_msg<>+0x18(SB)/8, $" run on "
+DATA	bad_proc_msg<>+0x20(SB)/8, $"processe"
+DATA	bad_proc_msg<>+0x28(SB)/8, $"rs with "
+DATA	bad_proc_msg<>+0x30(SB)/8, $"MMX supp"
+DATA	bad_proc_msg<>+0x38(SB)/4, $"ort."
+DATA	bad_proc_msg<>+0x3c(SB)/1, $0xa
+GLOBL	bad_proc_msg<>(SB), RODATA, $0x3d
+
 DATA	runtime·mainPC+0(SB)/4,$runtime·main(SB)
 GLOBL	runtime·mainPC(SB),RODATA,$4