From 97e8f2c69a89bda17a305805c9bcc99fae2bafa7 Mon Sep 17 00:00:00 2001
From: "Justin C. Miller" <justin@devjustinian.com>
Date: Wed, 13 Mar 2019 22:49:20 -0700
Subject: [PATCH] Add get_gsbase()

---
 src/kernel/debug.h              | 1 +
 src/kernel/debug.s              | 5 +++++
 src/kernel/memory_bootstrap.cpp | 9 ++++++---
 3 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/src/kernel/debug.h b/src/kernel/debug.h
index 260c783..d85a398 100644
--- a/src/kernel/debug.h
+++ b/src/kernel/debug.h
@@ -8,6 +8,7 @@ extern "C" {
 	uintptr_t get_rsp();
 	uintptr_t get_rip();
 	uintptr_t get_frame(int frame);
+	uintptr_t get_gsbase();
 
 }
 
diff --git a/src/kernel/debug.s b/src/kernel/debug.s
index ed1f7da..0fb0500 100644
--- a/src/kernel/debug.s
+++ b/src/kernel/debug.s
@@ -8,6 +8,11 @@ get_rip:
 	pop rax ; do the same thing as 'ret', except with 'jmp'
 	jmp rax ; with the return address still in rax
 
+global get_gsbase
+get_gsbase:
+	rdgsbase rax
+	ret
+
 global _halt
 _halt:
 	hlt
diff --git a/src/kernel/memory_bootstrap.cpp b/src/kernel/memory_bootstrap.cpp
index c84b873..8495dd6 100644
--- a/src/kernel/memory_bootstrap.cpp
+++ b/src/kernel/memory_bootstrap.cpp
@@ -198,9 +198,12 @@ memory_initialize(uint16_t scratch_pages, const void *memory_map, size_t map_len
 	// make sure the options we want in CR4 are set
 	uint64_t cr4;
 	__asm__ __volatile__ ( "mov %%cr4, %0" : "=r" (cr4) );
-	cr4 |= 0x00080; // Enable global pages
-	cr4 |= 0x00200; // Enable FXSAVE/FXRSTOR
-	cr4 |= 0x20000; // Enable PCIDs
+	cr4 |=
+		0x000080 | // Enable global pages
+		0x000200 | // Enable FXSAVE/FXRSTOR
+		0x010000 | // Enable FSGSBASE
+		0x020000 | // Enable PCIDs
+		0;
 	__asm__ __volatile__ ( "mov %0, %%cr4" :: "r" (cr4) );
 
 	// The bootloader reserved "scratch_pages" pages for page tables and