Lesson 23, step 6

Author: cfenollosa

23-fixes/README.md

@@ -39,6 +39,9 @@ C99 introduces standard fixed-width data types like `uint32_t`
 We need to include `<stdint.h>` which works even in `-ffreestanding` (but requires stdlibs)
 and use those data types instead of our own, then delete them on `type.h`
 
+We also delete the underscores around `__asm__` and `__volatile__` since they aren't needed.
+
+
 4. Improperly aligned `kmalloc`
 -------------------------------
 
@@ -53,12 +56,24 @@ For now, it will always return a new page-aligned memory block.
 5. Missing functions
 --------------------
 
+We will implement the missing `mem*` functions in following lessons
+
+
 6. Interrupt handlers
 ---------------------
-- also cli, sti in interrupt handlers
+`cli` is redundant, since we already established on the IDT entries if interrupts
+are enabled within a handler using the `idt_gate_t` flags.
+
+`sti` is also redundant, as `iret` loads the eflags value from the stack, which contains a 
+bit telling whether interrupts are on or off.
+In other words the interrupt handler automatically restores interrupts whether or not 
+interrupts were enabled before this interrupt
 
 
-7. Structs and attributes
--------------------------
+On `cpu/isr.h`, `struct registers_t` has a couple issues. 
+First, the alleged `esp` is renamed to `useless`.
+The value is useless because it has to do with the current stack context, not what was interrupted.
+Then, we rename `useresp` to `esp`
 
+Finally, we add `cld` just before `call isr_handler` on `cpu/interrupt.asm`
 

23-fixes/cpu/idt.c

@@ -13,5 +13,5 @@ void set_idt() {
     idt_reg.base = (uint32_t) &idt;
     idt_reg.limit = IDT_ENTRIES * sizeof(idt_gate_t) - 1;
     /* Don't make the mistake of loading &idt -- always load &idt_reg */
-    __asm__ __volatile__("lidtl (%0)" : : "r" (&idt_reg));
+    asm volatile("lidtl (%0)" : : "r" (&idt_reg));
 }

23-fixes/cpu/interrupt.asm

@@ -15,6 +15,7 @@ isr_common_stub:
 	mov gs, ax
 	
     ; 2. Call C handler
+    cld ; C code following the sysV ABI requires DF to be clear on function entry
 	call isr_handler
 	
     ; 3. Restore state
@@ -25,7 +26,6 @@ isr_common_stub:
 	mov gs, ax
 	popa
 	add esp, 8 ; Cleans up the pushed error code and pushed ISR number
-	sti
 	iret ; pops 5 things at once: CS, EIP, EFLAGS, SS, and ESP
 
 ; Common IRQ code. Identical to ISR code except for the 'call' 
@@ -47,7 +47,6 @@ irq_common_stub:
     mov gs, bx
     popa
     add esp, 8
-    sti
     iret 
 	
 ; We don't get information about which interrupt was caller
@@ -328,97 +327,81 @@ isr31:
 
 ; IRQ handlers
 irq0:
-	cli
 	push byte 0
 	push byte 32
 	jmp irq_common_stub
 
 irq1:
-	cli
 	push byte 1
 	push byte 33
 	jmp irq_common_stub
 
 irq2:
-	cli
 	push byte 2
 	push byte 34
 	jmp irq_common_stub
 
 irq3:
-	cli
 	push byte 3
 	push byte 35
 	jmp irq_common_stub
 
 irq4:
-	cli
 	push byte 4
 	push byte 36
 	jmp irq_common_stub
 
 irq5:
-	cli
 	push byte 5
 	push byte 37
 	jmp irq_common_stub
 
 irq6:
-	cli
 	push byte 6
 	push byte 38
 	jmp irq_common_stub
 
 irq7:
-	cli
 	push byte 7
 	push byte 39
 	jmp irq_common_stub
 
 irq8:
-	cli
 	push byte 8
 	push byte 40
 	jmp irq_common_stub
 
 irq9:
-	cli
 	push byte 9
 	push byte 41
 	jmp irq_common_stub
 
 irq10:
-	cli
 	push byte 10
 	push byte 42
 	jmp irq_common_stub
 
 irq11:
-	cli
 	push byte 11
 	push byte 43
 	jmp irq_common_stub
 
 irq12:
-	cli
 	push byte 12
 	push byte 44
 	jmp irq_common_stub
 
 irq13:
-	cli
 	push byte 13
 	push byte 45
 	jmp irq_common_stub
 
 irq14:
-	cli
 	push byte 14
 	push byte 46
 	jmp irq_common_stub
 
 irq15:
-	cli
 	push byte 15
 	push byte 47
 	jmp irq_common_stub

23-fixes/cpu/isr.h

@@ -74,9 +74,9 @@ extern void irq15();
 /* Struct which aggregates many registers */
 typedef struct {
    uint32_t ds; /* Data segment selector */
-   uint32_t edi, esi, ebp, esp, ebx, edx, ecx, eax; /* Pushed by pusha. */
+   uint32_t edi, esi, ebp, useless, ebx, edx, ecx, eax; /* Pushed by pusha. */
    uint32_t int_no, err_code; /* Interrupt number and error code (if applicable) */
-   uint32_t eip, cs, eflags, useresp, ss; /* Pushed by the processor automatically */
+   uint32_t eip, cs, eflags, esp, ss; /* Pushed by the processor automatically */
 } registers_t;
 
 void isr_install();

23-fixes/cpu/ports.c

@@ -13,7 +13,7 @@ uint8_t port_byte_in (uint16_t port) {
      *
      * Inputs and outputs are separated by colons
      */
-    __asm__("in %%dx, %%al" : "=a" (result) : "d" (port));
+    asm("in %%dx, %%al" : "=a" (result) : "d" (port));
     return result;
 }
 
@@ -23,15 +23,15 @@ void port_byte_out (uint16_t port, uint8_t data) {
      * However we see a comma since there are two variables in the input area
      * and none in the 'return' area
      */
-    __asm__ __volatile__("out %%al, %%dx" : : "a" (data), "d" (port));
+    asm volatile("out %%al, %%dx" : : "a" (data), "d" (port));
 }
 
 uint16_t port_word_in (uint16_t port) {
     uint16_t result;
-    __asm__("in %%dx, %%ax" : "=a" (result) : "d" (port));
+    asm("in %%dx, %%ax" : "=a" (result) : "d" (port));
     return result;
 }
 
 void port_word_out (uint16_t port, uint16_t data) {
-    __asm__ __volatile__("out %%ax, %%dx" : : "a" (data), "d" (port));
+    asm volatile("out %%ax, %%dx" : : "a" (data), "d" (port));
 }