Multiplication by two for segment selector index

1 files changed, 6 insertions, 2 deletions

diff --git a/arch/x86_64/include/arch/context_switching/interrupt_descriptor_table/segment_selector.hpp b/arch/x86_64/include/arch/context_switching/interrupt_descriptor_table/segment_selector.hpp
index 2c90152..b31f9e8 100644
--- a/arch/x86_64/include/arch/context_switching/interrupt_descriptor_table/segment_selector.hpp
+++ b/arch/x86_64/include/arch/context_switching/interrupt_descriptor_table/segment_selector.hpp
@@ -43,8 +43,12 @@ namespace teachos::arch::context_switching::interrupt_descriptor_table
     /**
      * @brief Constructor.
      *
-     * @param index Index into the local or global descriptor table. Processor multiplies the index value by 16 (number
-     * of bytes in segment descriptor) and adds the result to the base address.
+     * @param index Index into the local or global descriptor table. Processor multiplies the index value by 8 (number
+     * of bytes in 32-bit segment descriptor) and adds the result to the base GDT or LDT address. Because it only
+     * multiplies by 8, but we are using long mode the constructor additionally multiplies the given value by two. This
+     * is done because 64-bit segment descriptor are twice as big in size. If we wouldn't multiply by two, index 1 would
+     * result in the middle between the second part of the null entry and the first part of the code kernel segment and
+     * therefore be invalid.
      * @param flags Allows to set flags for the flags field using the unscoped enum contained in this class, used to
      * allow for direct integer conversion.
      */