Kernel: Fix signal generation

We need to have interrupts enabled when signal kills the process as
process does mutex locking. Also signals are now only checked when
returning to userspace in the same place where userspace segments are
loaded.

kernel/arch/i686/interrupts.S

@@ -1,20 +1,20 @@
-.macro maybe_load_kernel_segments, n
-	testb $3, \n(%esp)
-	jz 1f; jnp 1f
-
+.macro intr_header, n
+	pushal
+	testb $3, \n+8*4(%esp)
+	jz 1f
 	movw $0x10, %ax
 	movw %ax, %ds
 	movw %ax, %es
 	movw %ax, %fs
 	movw $0x28, %ax
 	movw %ax, %gs
-1:
+1:	cld
 .endm
 
-.macro maybe_load_userspace_segments, n
-	testb $3, \n(%esp)
-	jz 1f; jnp 1f
-
+.macro intr_footer, n
+	testb $3, \n+8*4(%esp)
+	jz 1f
+	call cpp_check_signal
 	movw $(0x20 | 3), %bx
 	movw %bx, %ds
 	movw %bx, %es
@@ -22,14 +22,11 @@
 	movw %bx, %fs
 	movw $(0x38 | 3), %bx
 	movw %bx, %gs
-1:
+1:	popal
 .endm
 
 isr_stub:
-	pushal
-	maybe_load_kernel_segments 44
-	cld
-
+	intr_header 12
 	movl %cr0, %eax; pushl %eax
 	movl %cr2, %eax; pushl %eax
 	movl %cr3, %eax; pushl %eax
@@ -57,15 +54,12 @@ isr_stub:
 	movl %ebp, %esp
 	addl $24, %esp
 
-	maybe_load_userspace_segments 44
-	popal
+	intr_footer 12
 	addl $8, %esp
 	iret
 
 irq_stub:
-	pushal
-	maybe_load_kernel_segments 44
-	cld
+	intr_header 12
 
 	movl 32(%esp), %edi # interrupt number
 
@@ -78,16 +72,13 @@ irq_stub:
 
 	movl %ebp, %esp
 
-	maybe_load_userspace_segments 44
-	popal
+	intr_footer 12
 	addl $8, %esp
 	iret
 
 .global asm_ipi_handler
 asm_ipi_handler:
-	pushal
-	maybe_load_kernel_segments 36
-	cld
+	intr_header 4
 
 	movl %esp, %ebp
 	andl $-16, %esp
@@ -96,15 +87,12 @@ asm_ipi_handler:
 
 	movl %ebp, %esp
 
-	maybe_load_userspace_segments 36
-	popal
+	intr_footer 4
 	iret
 
 .global asm_timer_handler
 asm_timer_handler:
-	pushal
-	maybe_load_kernel_segments 36
-	cld
+	intr_header 4
 
 	movl %esp, %ebp
 	andl $-16, %esp
@@ -113,8 +101,7 @@ asm_timer_handler:
 
 	movl %ebp, %esp
 
-	maybe_load_userspace_segments 36
-	popal
+	intr_footer 4
 	iret
 
 .macro isr n