kernel: turn into a PIE

3 files changed, 87 insertions, 31 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 9ddb4ed..821640c 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -46,6 +46,10 @@ target_link_libraries("kernel" PRIVATE
     "os::kern"
 )
 
+target_link_options("kernel" PRIVATE
+    "-no-pie"
+)
+
 target_disassemble("kernel")
 target_extract_debug_symbols("kernel")
 target_strip("kernel")
diff --git a/CMakePresets.json b/CMakePresets.json
index b01208a..8943a4d 100644
--- a/CMakePresets.json
+++ b/CMakePresets.json
@@ -5,7 +5,7 @@
       "name": "default",
       "binaryDir": "${sourceDir}/build",
       "generator": "Ninja Multi-Config",
-      "toolchainFile": "${workspaceFolder}/cmake/Platforms/x86_64.cmake",
+      "toolchainFile": "cmake/Platforms/x86_64.cmake",
       "cacheVariables": {
         "CMAKE_CONFIGURATION_TYPES": "Debug;MinSizeRel",
         "CMAKE_EXPORT_COMPILE_COMMANDS": "YES"
diff --git a/arch/x86_64/src/boot/boot.s b/arch/x86_64/src/boot/boot.s
index 728380d..ada6426 100644
--- a/arch/x86_64/src/boot/boot.s
+++ b/arch/x86_64/src/boot/boot.s
@@ -71,16 +71,7 @@ stack_top:
 global_descriptor_table: .quad 0
 global_descriptor_table_code = . - global_descriptor_table
 .quad (1<<43) | (1<<44) | (1<<47) | (1<<53)
-
-/**
- * We also need a pointer that we can load into the GDTR.
- *
- * The pointer consists of a word describing the size of the table minus 1 and
- * the pointer to the actual table.
- */
-global_descriptor_table_pointer:
-.word . - global_descriptor_table - 1
-.quad global_descriptor_table
+global_descriptor_table_end:
 
 /**
  * We are going to print some messages in case we panic during boot, so we are
@@ -130,7 +121,12 @@ _panic:
     push %ebp
     mov %esp, %ebp
 
-    push message_prefix_panic
+    call .Lpanic_get_ip
+.Lpanic_get_ip:
+    pop %eax
+    lea (message_prefix_panic - .Lpanic_get_ip)(%eax), %eax
+
+    push %eax
     push $0x4f
     call _print
     add $8, %esp
@@ -155,10 +151,17 @@ _print:
 
     push %ebx
     push %esi
+    push %edi
+
+    call .Lprint_get_ip
+.Lprint_get_ip:
+    pop %edi
+    lea (vga_buffer_pointer - .Lprint_get_ip)(%edi), %edi
+
     mov 8(%ebp), %eax
     mov 12(%ebp), %ebx
     mov $0, %ecx
-    mov (vga_buffer_pointer), %esi
+    mov (%edi), %esi
 
 .Lprint_loop:
     mov (%ebx, %ecx), %dl
@@ -171,9 +174,11 @@ _print:
 
 .Lupdate_vga_buffer_address:
     shl $1, %ecx
-    add %ecx, (vga_buffer_pointer)
+    add %ecx, %esi
+    mov %esi, (%edi)
 
 .Lprint_end:
+    pop %edi
     pop %esi
     pop %ebx
     mov %ebp, %esp
@@ -187,7 +192,12 @@ _print:
  */
 .global _start
 _start:
-    mov $stack_top, %esp
+    call .Lstart_get_ip
+.Lstart_get_ip:
+    pop %esi
+    lea (stack_top - .Lstart_get_ip)(%esi), %ebx
+
+    mov %ebx, %esp
     mov %esp, %ebp
 
     call assert_loaded_by_multiboot2_loader
@@ -197,8 +207,19 @@ _start:
     call enable_paging
     call enable_sse
 
-    lgdt (global_descriptor_table_pointer)
-    jmp $global_descriptor_table_code, $_transition_to_long_mode
+    sub $10, %esp
+    lea (global_descriptor_table - .Lstart_get_ip)(%esi), %eax
+    movw $(global_descriptor_table_end - global_descriptor_table -1), (%esp)
+    mov %eax, 2(%esp)
+    movl $0, 6(%esp)
+
+    lgdt (%esp)
+    add $10, %esp
+
+    lea (_transition_to_long_mode - .Lstart_get_ip)(%esi), %eax
+    pushl $global_descriptor_table_code
+    pushl %eax
+    lret
 
     call halt
 
@@ -217,7 +238,11 @@ assert_cpu_supports_long_mode:
     jz .Llong_mode_assertion_failed
     ret
 .Llong_mode_assertion_failed:
-    push $mesage_long_mode_not_supported
+    call .Lassert_cpu_supports_long_mode_fail_get_ip
+.Lassert_cpu_supports_long_mode_fail_get_ip:
+    pop %eax
+    lea (mesage_long_mode_not_supported - .Lassert_cpu_supports_long_mode_fail_get_ip)(%eax), %eax
+    push %eax
     call _panic
 
 /**
@@ -245,7 +270,11 @@ assert_cpuid_instruction_is_supported:
     je .Lcpuid_assertion_fail
     ret
 .Lcpuid_assertion_fail:
-    push $message_cpuid_instruction_no_supported
+    call .Lassert_cpuid_instruction_is_supported_fail_get_ip
+.Lassert_cpuid_instruction_is_supported_fail_get_ip:
+    pop %eax
+    lea (message_cpuid_instruction_no_supported - .Lassert_cpuid_instruction_is_supported_fail_get_ip)(%eax), %eax
+    push %eax
     call _panic
 
 /**
@@ -259,10 +288,18 @@ assert_loaded_by_multiboot2_loader:
     cmp $0x36d76289, %eax                   /* Check if we received the
                                                expected magic */
     jne .Lmultiboot2_assertion_fail         /* Panic otherwise */
-    mov %ebx, multiboot_information_pointer /* Store the MBI pointer */
+    call .Lassert_loaded_by_multiboot2_loader_get_ip
+.Lassert_loaded_by_multiboot2_loader_get_ip:
+    pop %eax
+    lea (multiboot_information_pointer - .Lassert_loaded_by_multiboot2_loader_get_ip)(%eax), %eax
+    mov %ebx, (%eax) /* Store the MBI pointer */
     ret
 .Lmultiboot2_assertion_fail:
-    push $message_not_loaded_by_multiboot2
+    call .Lassert_loaded_by_multiboot2_loader_fail_get_ip
+.Lassert_loaded_by_multiboot2_loader_fail_get_ip:
+    pop %eax
+    lea (message_not_loaded_by_multiboot2 - .Lassert_loaded_by_multiboot2_loader_fail_get_ip)(%eax), %eax
+    push %eax
     call _panic
 
 /**
@@ -272,7 +309,10 @@ assert_loaded_by_multiboot2_loader:
  * set up for use.
  */
 enable_paging:
-    mov $page_map_level_4, %eax
+    call .Lenable_paging_get_ip
+.Lenable_paging_get_ip:
+    pop %eax
+lea (page_map_level_4 - .Lenable_paging_get_ip)(%eax), %eax
     mov %eax, %cr3
 
     /* Enable Physical Address Extension */
@@ -316,37 +356,46 @@ enable_sse:
  * page map entries.
  */
 prepare_page_maps:
+    call .Lprepare_page_maps_get_ip
+.Lprepare_page_maps_get_ip:
+    pop %edi
     /* Map the P4 table recursively */
-    mov $page_map_level_4, %eax
+    lea (page_map_level_4 - .Lprepare_page_maps_get_ip)(%edi), %eax
+    mov %eax, %ebx
     or $0b11, %eax /* Write present + writable flags into eax register */
-    mov %eax, (page_map_level_4 + 511 * 8)
+    mov %eax, (511 * 8)(%ebx)
 
     /* Add an entry to the PML4, pointing to the PML3 */
-    mov $page_map_level_3, %eax
+    lea (page_map_level_3 - .Lprepare_page_maps_get_ip)(%edi), %eax
+    lea (page_map_level_4 - .Lprepare_page_maps_get_ip)(%edi), %ebx
     or $0x3, %eax
-    mov %eax, (page_map_level_4 + ((0x0000000000100000 >> 39) & 0x1ff) * 8)
+    mov %eax, (((0x0000000000100000 >> 39) & 0x1ff) * 8)(%ebx)
 
     /* Add an entry to the PML3, pointing to the PML2 */
-    mov $page_map_level_2, %eax
+    lea (page_map_level_2 - .Lprepare_page_maps_get_ip)(%edi), %eax
+    lea (page_map_level_3 - .Lprepare_page_maps_get_ip)(%edi), %ebx
     or $0x3, %eax
-    mov %eax, (page_map_level_3 + ((0x0000000000100000 >> 30) & 0x1ff) * 8)
+    mov %eax, (((0x0000000000100000 >> 30) & 0x1ff) * 8)(%ebx)
 
     xor %ecx, %ecx
 
-    mov $_end_linear, %esi
+    push %esi
+    lea (_end_linear - .Lprepare_page_maps_get_ip)(%edi), %esi
     shr $21, %esi
     add $2, %esi
 
 .Lmap_pages:
+    lea (page_map_level_2 - .Lprepare_page_maps_get_ip)(%edi), %ebx
     mov $(1 << 21), %eax
     mul %ecx
     or $((1 << 0) | (1 << 1) | (1 << 7)), %eax
-    mov %eax, page_map_level_2(,%ecx,8)
+    mov %eax, (%ebx,%ecx,8)
 
     inc %ecx
     cmp %esi, %ecx
     jne .Lmap_pages
 
+    pop %esi
     ret
 
 .section .boot_text, "ax", @progbits
@@ -360,7 +409,10 @@ _transition_to_long_mode:
     mov %rax, %fs
     mov %rax, %gs
 
-    movl $0xb8000, (vga_buffer_pointer)
+    leaq vga_buffer_pointer(%rip), %rax
+    movl $0xb8000, (%rax)
+
+    xor %rax, %rax
 
     call _init