Kernel: Add functions to push and pop the interrupt state

This can be useful when you want to disable interrupts, but then only enable them back if they were previously enabled.

kernel/include/interrupts/Interrupts.h

@@ -8,4 +8,10 @@ namespace Interrupts
 
     bool is_in_handler();
     void return_from_handler(Context* context);
+
+    bool are_enabled();
+    bool were_enabled();
+    void push_and_disable();
+    void push_and_enable();
+    void pop();
 }

kernel/include/misc/utils.h

@@ -5,4 +5,6 @@ namespace Utilities
 {
     uint64_t get_blocks_from_size(uint64_t blocksize,
                                   uint64_t size); // Returns how many blocks of size blocksize does size occupy.
+
+    uint64_t get_rflags();
 }

kernel/src/interrupts/Interrupts.cpp

@@ -1,4 +1,5 @@
 #include "interrupts/Interrupts.h"
+#include "misc/utils.h"
 #include "trace/StackTracer.h"
 
 void Interrupts::disable()
@@ -24,4 +25,35 @@ void Interrupts::return_from_handler(Context* context)
                  "jmp _asm_interrupt_exit"
                  :
                  : "r"(context));
+}
+
+bool Interrupts::are_enabled()
+{
+    return (Utilities::get_rflags() & 0x200) > 0;
+}
+
+static bool saved_interrupt_state;
+
+void Interrupts::push_and_disable()
+{
+    saved_interrupt_state = are_enabled();
+    disable();
+}
+
+void Interrupts::push_and_enable()
+{
+    saved_interrupt_state = are_enabled();
+    enable();
+}
+
+void Interrupts::pop()
+{
+    if (saved_interrupt_state && !are_enabled()) enable();
+    else if (!saved_interrupt_state && are_enabled())
+        disable();
+}
+
+bool Interrupts::were_enabled()
+{
+    return saved_interrupt_state;
 }

kernel/src/main.asm

@@ -25,4 +25,10 @@ asm_enable_sse:
     mov rax, cr4
     or ax, 3 << 9
     mov cr4, rax
+    ret
+
+global asm_get_rflags
+asm_get_rflags:
+    pushfq
+    pop rax
     ret

kernel/src/misc/utils.cpp

@@ -3,4 +3,10 @@
 uint64_t Utilities::get_blocks_from_size(uint64_t blocksize, uint64_t size)
 {
     return (size + (blocksize - 1)) / blocksize;
+}
+
+extern "C" uint64_t asm_get_rflags();
+uint64_t Utilities::get_rflags()
+{
+    return asm_get_rflags();
 }