user: implement mlibc as the libc, finally.

It's finally done..

Signed-off-by: kaguya <vpshinomiya@protonmail.com>

user/include/mlibc/options/internal/x86_64/fenv.S

@@ -0,0 +1,102 @@
+# The functions below are taken from musl.
+.global feclearexcept
+.type feclearexcept,@function
+feclearexcept:
+	# maintain exceptions in the sse mxcsr, clear x87 exceptions
+	mov %edi,%ecx
+	and $0x3f,%ecx
+	fnstsw %ax
+	test %eax,%ecx
+	jz 1f
+	fnclex
+1:	stmxcsr -8(%rsp)
+	and $0x3f,%eax
+	or %eax,-8(%rsp)
+	test %ecx,-8(%rsp)
+	jz 1f
+	not %ecx
+	and %ecx,-8(%rsp)
+	ldmxcsr -8(%rsp)
+1:	xor %eax,%eax
+	ret
+
+.global feraiseexcept
+.type feraiseexcept,@function
+feraiseexcept:
+	and $0x3f,%edi
+	stmxcsr -8(%rsp)
+	or %edi,-8(%rsp)
+	ldmxcsr -8(%rsp)
+	xor %eax,%eax
+	ret
+
+.global __fesetround
+.hidden __fesetround
+.type __fesetround,@function
+__fesetround:
+	push %rax
+	xor %eax,%eax
+	mov %edi,%ecx
+	fnstcw (%rsp)
+	andb $0xf3,1(%rsp)
+	or %ch,1(%rsp)
+	fldcw (%rsp)
+	stmxcsr (%rsp)
+	shl $3,%ch
+	andb $0x9f,1(%rsp)
+	or %ch,1(%rsp)
+	ldmxcsr (%rsp)
+	pop %rcx
+	ret
+
+.global fegetround
+.type fegetround,@function
+fegetround:
+	push %rax
+	stmxcsr (%rsp)
+	pop %rax
+	shr $3,%eax
+	and $0xc00,%eax
+	ret
+
+.global fegetenv
+.type fegetenv,@function
+fegetenv:
+	xor %eax,%eax
+	fnstenv (%rdi)
+	stmxcsr 28(%rdi)
+	ret
+
+.global fesetenv
+.type fesetenv,@function
+fesetenv:
+	xor %eax,%eax
+	inc %rdi
+	jz 1f
+	fldenv -1(%rdi)
+	ldmxcsr 27(%rdi)
+	ret
+1:	push %rax
+	push %rax
+	pushq $0xffff
+	pushq $0x37f
+	fldenv (%rsp)
+	pushq $0x1f80
+	ldmxcsr (%rsp)
+	add $40,%rsp
+	ret
+
+.global fetestexcept
+.type fetestexcept,@function
+fetestexcept:
+	and $0x3f,%edi
+	push %rax
+	stmxcsr (%rsp)
+	pop %rsi
+	fnstsw %ax
+	or %esi,%eax
+	and %edi,%eax
+	ret
+
+.section .note.GNU-stack,"",%progbits
+