Fix running on bochs by forcing x86 pentium codegen

kernel/make.i386_pc.flags

@@ -1,6 +1,7 @@
 clang_res_dir := $(shell $(cc) -print-resource-dir)
 
 kernel_cflags   := --target=i386-none-elf \
+                   -march=pentium \
                    -nostdinc \
                    -nostdlib \
                    -ffreestanding \
@@ -8,7 +9,8 @@ kernel_cflags   := --target=i386-none-elf \
                    -std=c11 \
                    -pedantic \
                    -Wall \
-                   -Wextra
+                   -Wextra \
+                   -ffunction-sections -fdata-sections
 
 ifeq ($(build),debug)
 kernel_cflags   += -O0 -g
@@ -27,6 +29,8 @@ kernel_ldflags  := -mcpu=i386 \
                    -flto \
                    -static \
                    -Wl,--build-id=none \
+                   -Wl,--gc-sections \
+                   -Wl,--strip-all \
                    $(clang_res_dir)/lib/*/libclang_rt.builtins-i386.a
 
 ifeq ($(build),debug)

kernel/platform/i386_pc/boot/bootmain.c

@@ -79,7 +79,7 @@ static void pmm_init1(void) {
 }
 
 void bootmain(void *mbootptr) {
-  multiboot_set((struct multiboot *)VIRT(mbootptr));
+  multiboot_set((struct multiboot *)((uptr_t)mbootptr + VIRT_BASE));
 
   cpu_init();
 

kernel/platform/i386_pc/link.ld

@@ -39,11 +39,11 @@ SECTIONS {
   . = 0x00100000;
 
   .multiboot ALIGN(4K): {
-    *(.multiboot)
+    KEEP(*(.multiboot))
   }
 
   .boot ALIGN(4K) : {
-    *(.boot)
+    KEEP(*(.boot))
   }
 
   . += VIRT_BASE;
@@ -64,5 +64,11 @@ SECTIONS {
     *(.bss)
   }
 
+  /DISCARD/ : {
+    *(.eh_frame)
+    *(.comment)
+    *(.note.gnu.build-id)
+  }
+
   __kernel_end = .;
 }

kernel/platform/i386_pc/sys/cpu.c

@@ -89,6 +89,7 @@ static void tss_init(void) {
   tss.fs = 0x10 | 0x3;
   tss.fs = 0x10 | 0x3;
   tss.ss = 0x10 | 0x3;
+  tss.iomap = sizeof(tss);
 
   tss_flush();
 }

kernel/platform/i386_pc/sys/mm.h

@@ -38,7 +38,6 @@ SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #include <sync/spinlock.h>
 
 #define VIRT_BASE   0xC0000000
-#define VIRT(x)     (((uptr_t)(x)) + VIRT_BASE)
 
 #define PAGE_SIZE 0x1000