From 8b88f3f7fd143fc542a5118d50a7a981464270d5 Mon Sep 17 00:00:00 2001
From: Aqua-sama <aqua@iserlohn-fortress.net>
Date: Mon, 15 Mar 2021 21:07:59 +0200
Subject: Fix compile failure without -O2

Linking fails without lto on
---
 makefile           |  2 +-
 src/gdt.cc         | 18 +++++++-----------
 src/gdt.h          |  6 ++++--
 src/memory.cc      |  5 +++++
 toolchain.makefile |  7 ++++---
 5 files changed, 21 insertions(+), 17 deletions(-)

diff --git a/makefile b/makefile
index 5ebde01..5f2d833 100644
--- a/makefile
+++ b/makefile
@@ -18,7 +18,6 @@ CXX_SYSTEM_INCLUDE := $(addprefix -isystem, $(CXX_SYSTEM_INCLUDE))
 
 $(OBJ_DIR)/glitch.elf: $(autogen) $(AS_OBJ) $(CXX_OBJ) linker.ld
 	@echo "  LD   $@"
-	@mkdir -p $(OBJ_DIR)/thinlto_cache
 	@$(LD) $(LD_FLAGS) -o $@ $(AS_OBJ) $(CXX_OBJ)
 
 $(AS_OBJ): $(OBJ_DIR)/%.o: %.S
@@ -39,6 +38,7 @@ $(CXX_TEST_OBJ): $(OBJ_DIR)/%.o : %.cc
 
 clean:
 	@rm -rf $(autogen) $(AS_OBJ) $(CXX_OBJ) $(CXX_DEP) $(CXX_TEST_OBJ) $(OBJ_DIR)/glitch.elf $(OBJ_DIR)/isodir
+	@rm -rf $(OBJ_DIR)/*_cache
 	@make -C tools/kconfig OBJ_DIR=$(CURDIR)/$(OBJ_DIR)/kconfig clean
 
 # testing
diff --git a/src/gdt.cc b/src/gdt.cc
index 7b5e3df..726a7d7 100644
--- a/src/gdt.cc
+++ b/src/gdt.cc
@@ -14,9 +14,9 @@ constexpr uint32_t kseg_start = 0;
 constexpr uint32_t kseg_sz = 0xffffffff;
 
 __attribute__((section(".constinit"))) static GDT::SegmentDescriptor segments[256]{
-    [GDT::null0] = seg::make<null_sz>(0, {}),
-    [GDT::kcode] = seg::make<kseg_sz>(kseg_start, {.r_w = true, .exe = true, .segment = true, .present = true}),
-    [GDT::kdata] = seg::make<kseg_sz>(kseg_start, {.r_w = true, .segment = true, .present = true}),
+    seg::make<null_sz>(0, {}),
+    seg::make<kseg_sz>(kseg_start, {.r_w = true, .exe = true, .segment = true, .present = true}),
+    seg::make<kseg_sz>(kseg_start, {.r_w = true, .segment = true, .present = true}),
 };
 
 GDT::GDT() {
@@ -24,23 +24,19 @@ GDT::GDT() {
   asm volatile("lgdt %0" : : "p"(gdtr));
 
   // flush the segment registers
-  const auto cs = descriptor(kcode);
-  const auto ds = descriptor(kdata);
+  constexpr auto cs = GDT::descriptor(kcode);
+  constexpr auto ds = GDT::descriptor(kdata);
 
   asm volatile(
-      "jmp %0,$.reload_cs\n\t"  // far jump takes cs
+      "jmpl %0,$.reload_cs\n\t"  // far jump: cs,location
       ".reload_cs:\n\t"
       "  mov %1, %%ds\n\t"  // ds
       "  mov %1, %%es\n\t"
       "  mov %1, %%fs\n\t"
       "  mov %1, %%gs\n\t"
       "  mov %1, %%ss\n\t" ::"i"(cs),
-      "r"(ds));
+      "rm"(ds));
 
   printk("GDT installed at ", uhex{gdtr.base}, '\n');
 }
 
-uint16_t GDT::descriptor(GDT::SegmentMap i) const {
-  return static_cast<uint16_t>(reinterpret_cast<const uint32_t>(&segments[i]) -
-                               reinterpret_cast<const uint32_t>(&segments));
-}
diff --git a/src/gdt.h b/src/gdt.h
index 6aeaa33..4deeec3 100644
--- a/src/gdt.h
+++ b/src/gdt.h
@@ -95,11 +95,13 @@ public:
 
     unsigned int base_31_24 : 8 = 0;   // high bits of segment address
   } __attribute__((packed));
-  enum SegmentMap { null0, kcode, kdata };
+  enum SegmentMap { null0 = 0, kcode = 1, kdata = 2 };
 
   GDT();
   ~GDT() = default;
 
-  uint16_t descriptor(SegmentMap) const;
+  static constexpr uint16_t descriptor(GDT::SegmentMap i) {
+    return static_cast<uint16_t>(i * sizeof(SegmentDescriptor));
+  }
 };
 
diff --git a/src/memory.cc b/src/memory.cc
index a2a2561..2d440a3 100644
--- a/src/memory.cc
+++ b/src/memory.cc
@@ -4,3 +4,8 @@ void operator delete(void*) {
   printk("Calling delete\n");
   abort();
 }
+
+extern "C" void __cxa_pure_virtual() {
+  printk("__cxa_pure_virtual\n");
+  abort();
+}
diff --git a/toolchain.makefile b/toolchain.makefile
index d8f09f7..ce8fdc6 100644
--- a/toolchain.makefile
+++ b/toolchain.makefile
@@ -8,13 +8,14 @@ AS       := clang
 AS_FLAGS :=
 
 LD       := ld.lld
-LD_FLAGS := -T linker.ld --thinlto-cache-dir=$(OBJ_DIR)/thinlto_cache
+LD_FLAGS := -nostdlib -T linker.ld --thinlto-cache-dir=$(OBJ_DIR)/thinlto_cache
+# TODO: linking fails with -O0 and -O1 without -flto=thin
 
 CXX         := clang++
 TEST_CXX    := clang++
-CXX_FLAGS   := -std=c++20 -g \
+CXX_FLAGS   := -std=c++20 -g -O2 -flto=thin \
 	       -mkernel -ffreestanding -nostdlib -nostdinc -nostdinc++ \
-               -Wall -Wextra -Werror=pedantic -O2 -flto=thin \
+	       -Wall -Wextra -Werror=pedantic \
 	       -Werror=date-time \
 	       -Werror=shadow-all \
 	       -Wold-style-cast -Wconversion \
-- 
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