From 393808e198a2f6bf32f0af235f13f76e2c08a894 Mon Sep 17 00:00:00 2001
From: Stefan Lankes <lankes@lfbs.rwth-aachen.de>
Date: Thu, 9 Jun 2011 08:18:12 +0200
Subject: [PATCH] fix bug in the initializtion of the BSS section

- DO NOT LONGER USE the compiler flag "-fno-zero-initialized-in-bss"
---
 Makefile.example            |  4 ++--
 arch/x86/kernel/entry.asm   |  2 +-
 arch/x86/kernel/gdt.c       |  4 ++--
 arch/x86/kernel/multiboot.c |  2 +-
 kernel/init.c               | 12 ++++++++++++
 link.ld                     |  5 ++---
 6 files changed, 20 insertions(+), 9 deletions(-)

diff --git a/Makefile.example b/Makefile.example
index 71ff1725..3e87db1e 100644
--- a/Makefile.example
+++ b/Makefile.example
@@ -26,9 +26,9 @@ MAKE = make
 NASMFLAGS = -felf32 -g
 INCLUDE = -I$(TOPDIR)/include -I$(TOPDIR)/arch/$(ARCH)/include -I$(TOPDIR)/lwip/src/include -I$(TOPDIR)/lwip/src/include/ipv4 -I$(TOPDIR)/drivers
 # Compiler options for final code
-CFLAGS = -g -m32 -march=i586 -Wall -O2 -fno-zero-initialized-in-bss -fno-builtin -fstrength-reduce -fomit-frame-pointer -finline-functions -nostdinc $(INCLUDE) -fno-stack-protector
+CFLAGS = -g -m32 -march=i586 -Wall -O2 -fno-builtin -fstrength-reduce -fomit-frame-pointer -finline-functions -nostdinc $(INCLUDE) -fno-stack-protector
 # Compiler options for debuuging
-#CFLAGS = -g -O -m32 -march=i586 -Wall -fno-zero-initialized-in-bss -fno-builtin -DWITH_FRAME_POINTER -nostdinc $(INCLUDE) -fno-stack-protector
+#CFLAGS = -g -O -m32 -march=i586 -Wall -fno-builtin -DWITH_FRAME_POINTER -nostdinc $(INCLUDE) -fno-stack-protector
 ARFLAGS = rsv
 RM = rm -rf
 LDFLAGS = -T link.ld -z max-page-size=4096 --defsym __BUILD_DATE=$(shell date +'%Y%m%d') --defsym __BUILD_TIME=$(shell date +'%H%M%S')
diff --git a/arch/x86/kernel/entry.asm b/arch/x86/kernel/entry.asm
index 5610c6b8..6fb00652 100644
--- a/arch/x86/kernel/entry.asm
+++ b/arch/x86/kernel/entry.asm
@@ -73,7 +73,7 @@ stublet:
 ; clears the current pgd entry
     xor eax, eax
     mov cr3, eax
-; disable SSE support (TODO)
+; at this stage, we disable the SSE support
     mov eax, cr4
     and eax, 0xfffbf9ff
     mov cr4, eax
diff --git a/arch/x86/kernel/gdt.c b/arch/x86/kernel/gdt.c
index 5be409c6..53a83b95 100644
--- a/arch/x86/kernel/gdt.c
+++ b/arch/x86/kernel/gdt.c
@@ -28,10 +28,10 @@
 
 gdt_ptr_t				gp;
 static tss_t				task_state_segments[MAX_TASKS] __attribute__ ((aligned (PAGE_SIZE)));
-static unsigned char			kstacks[MAX_TASKS][KERNEL_STACK_SIZE] __attribute__ ((aligned (PAGE_SIZE)));
+static unsigned char			kstacks[MAX_TASKS][KERNEL_STACK_SIZE] __attribute__ ((aligned (PAGE_SIZE) section (".data")));
 // currently, our kernel has full access to the ioports
 static gdt_entry_t			gdt[GDT_ENTRIES] = {[0 ... GDT_ENTRIES-1] = {0, 0, 0, 0, 0, 0}};
-unsigned char* 				default_stack_pointer = kstacks[0] + KERNEL_STACK_SIZE - sizeof(size_t);
+unsigned char* 				default_stack_pointer __attribute__ ((section (".data"))) = kstacks[0] + KERNEL_STACK_SIZE - sizeof(size_t);
 
 /* 
  * This is in start.asm. We use this to properly reload
diff --git a/arch/x86/kernel/multiboot.c b/arch/x86/kernel/multiboot.c
index d57b5f96..ec124479 100644
--- a/arch/x86/kernel/multiboot.c
+++ b/arch/x86/kernel/multiboot.c
@@ -37,7 +37,7 @@
  */
 
 /** Global multiboot information structure pointer */
-multiboot_info_t*	mb_info = NULL;
+multiboot_info_t*	mb_info __attribute__ ((section (".data"))) = NULL;
 #endif
 
 /** @brief initialization procedure for Multiboot information structure
diff --git a/kernel/init.c b/kernel/init.c
index 2ba3b81f..c4dea9b7 100644
--- a/kernel/init.c
+++ b/kernel/init.c
@@ -43,10 +43,22 @@ void ping_init(void);
 
 static volatile int done = 0;
 
+/* 
+ * Note that linker symbols are not variables, they have no memory allocated for
+ * maintaining a value, rather their address is their value.
+ */
+extern const void bss_start;
+extern const void bss_end;
+
 int lowlevel_init(void)
 {
+	// initialize .bss section
+	memset((void*)&bss_start, 0x00, ((size_t) &bss_end - (size_t) &bss_start));
+
 	koutput_init();
 
+	//kprintf("Now, the BSS section (0x%x - 0x%x) is initialized.\n", (size_t) &bss_start, (size_t) &bss_end);
+
 	return 0;
 }
 
diff --git a/link.ld b/link.ld
index bbb2a9d4..ad03b8f5 100644
--- a/link.ld
+++ b/link.ld
@@ -13,9 +13,6 @@ SECTIONS
   .text ALIGN(4096) : AT(ADDR(.text)) {
     *(.text)
   }
-  .rdata ALIGN(4096) : AT(ADDR(.rdata)) {
-    *(.rdata)
-  }
   .rodata ALIGN(4096) : AT(ADDR(.rodata)) {
     *(.rodata)
     *(.rodata.*)
@@ -23,8 +20,10 @@ SECTIONS
   .data ALIGN(4096) : AT(ADDR(.data)) {
     *(.data)
   }
+  bss_start = .;
   .bss ALIGN(4096) : AT(ADDR(.bss)) {
     *(.bss)
   }
+  bss_end = .;
   kernel_end = .;
 }