Kernel: Fix struct layout for interrupt entries on x86_64

Author: https://github.com/gunnarbeutner
Commit: https://github.com/SerenityOS/serenity/commit/36ce2a2b765
Pull-request: https://github.com/SerenityOS/serenity/pull/8317

Kernel/Arch/x86/RegisterState.h

@@ -47,11 +47,11 @@ struct [[gnu::packed]] RegisterState {
     FlatPtr r14;
     FlatPtr r15;
 #endif
+    u16 exception_code;
+    u16 isr_number;
 #if ARCH(X86_64)
     u32 padding;
 #endif
-    u16 exception_code;
-    u16 isr_number;
 #if ARCH(I386)
     FlatPtr eip;
 #else

Kernel/Arch/x86/x86_64/InterruptEntry.cpp

@@ -14,7 +14,11 @@ asm(
     "interrupt_common_asm_entry: \n"
     // add the padding field in RegisterState
     "    subq $4, %rsp\n"
-    "    movl $0, 0(%rsp)\n"
+    "    pushq %rax\n"
+    "    movl 12(%rsp), %eax\n"
+    "    movl $0, 12(%rsp)\n"
+    "    movl %eax, 8(%rsp)\n"
+    "    popq %rax\n"
     // save all the other registers
     "    pushq %r15\n"
     "    pushq %r14\n"