From 4c8e066aae6a8f69bb24994b1ce45d305c8469f5 Mon Sep 17 00:00:00 2001
From: Stefan Lankes <slankes@eonerc.rwth-aachen.de>
Date: Sat, 4 Nov 2017 12:46:57 +0100
Subject: [PATCH] allocate stacks on demand, reduce the size of the BSS section

---
 arch/x86/include/asm/gdt.h | 26 +++++++++++++++-----------
 arch/x86/kernel/gdt.c      | 27 +++++++++++++++++++++------
 arch/x86/mm/memory.c       |  3 +++
 3 files changed, 39 insertions(+), 17 deletions(-)

diff --git a/arch/x86/include/asm/gdt.h b/arch/x86/include/asm/gdt.h
index 1f8c7f01d..3f8b462ca 100644
--- a/arch/x86/include/asm/gdt.h
+++ b/arch/x86/include/asm/gdt.h
@@ -51,26 +51,26 @@ extern "C" {
 #define GDT_FLAG_TSS_BUSY	0x02
 
 #define GDT_FLAG_SEGMENT	0x10
-/// Privilege level: Ring 0 
+/// Privilege level: Ring 0
 #define GDT_FLAG_RING0		0x00
 /// Privilege level: Ring 1
 #define GDT_FLAG_RING1		0x20
-/// Privilege level: Ring 2 
+/// Privilege level: Ring 2
 #define GDT_FLAG_RING2		0x40
-/// Privilege level: Ring 3 
+/// Privilege level: Ring 3
 #define GDT_FLAG_RING3		0x60
 /// Segment is present
 #define GDT_FLAG_PRESENT        0x80
 /// Segment was accessed
 #define GDT_FLAG_ACCESSED       0x01
-/** 
- * @brief Granularity of segment limit 
+/**
+ * @brief Granularity of segment limit
  * - set: segment limit unit is 4 KB (page size)
  * - not set: unit is bytes
  */
 #define GDT_FLAG_4K_GRAN	0x80
 /**
- * @brief Default operand size 
+ * @brief Default operand size
  * - set: 32 bit
  * - not set: 16 bit
  */
@@ -78,7 +78,7 @@ extern "C" {
 #define GDT_FLAG_32_BIT		0x40
 #define GDT_FLAG_64_BIT		0x20
 
-/** @brief Defines a GDT entry 
+/** @brief Defines a GDT entry
  *
  * A global descriptor table entry consists of:
  * - 32 bit base address (chunkwise embedded into this structure)
@@ -115,16 +115,16 @@ typedef struct {
 
 #if GDT_ENTRIES > 8192
 #error Too many GDT entries!
-#endif 
+#endif
 
 /** @brief Installs the global descriptor table
  *
  * The installation involves the following steps:
- * - set up the special GDT pointer 
+ * - set up the special GDT pointer
  * - set up the entries in our GDT
- * - finally call gdt_flush() in our assembler file 
+ * - finally call gdt_flush() in our assembler file
  *   in order to tell the processor where the new GDT is
- * - update the new segment registers 
+ * - update the new segment registers
  */
 void gdt_install(void);
 
@@ -143,6 +143,10 @@ void gdt_set_gate(int num, unsigned long base, unsigned long limit,
 void configure_gdt_entry(gdt_entry_t *dest_entry, unsigned long base, unsigned long limit,
 		unsigned char access, unsigned char gran);
 
+/** @brief Initialize the task state segments
+ */
+void tss_init(void);
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/arch/x86/kernel/gdt.c b/arch/x86/kernel/gdt.c
index dca9c9f3b..b4e25006c 100644
--- a/arch/x86/kernel/gdt.c
+++ b/arch/x86/kernel/gdt.c
@@ -31,6 +31,7 @@
 #include <hermit/tasks.h>
 #include <hermit/errno.h>
 #include <hermit/processor.h>
+#include <hermit/logging.h>
 #include <asm/gdt.h>
 #include <asm/tss.h>
 #include <asm/page.h>
@@ -41,7 +42,6 @@ gdt_ptr_t		gp;
 // 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}};
 static tss_t		task_state_segments[MAX_CORES] __attribute__ ((aligned (PAGE_SIZE)));
-static uint8_t		stack_table[MAX_CORES][KERNEL_STACK_SIZE*MAX_IST] __attribute__ ((aligned (PAGE_SIZE)));
 
 extern const void boot_stack;
 
@@ -94,7 +94,8 @@ void gdt_install(void)
 {
 	int i, num = 0;
 
-	memset(task_state_segments, 0x00, MAX_CORES*sizeof(tss_t));
+	// part of bss => already initialized
+	//memset(task_state_segments, 0x00, MAX_CORES*sizeof(tss_t));
 
 	/* Setup the GDT pointer and limit */
 	gp.limit = (sizeof(gdt_entry_t) * GDT_ENTRIES) - 1;
@@ -148,10 +149,6 @@ void gdt_install(void)
 	 */
 	for(i=0; i<MAX_CORES; i++) {
 		task_state_segments[i].rsp0 = (size_t)&boot_stack + (i+1) * KERNEL_STACK_SIZE - 0x10;
-		task_state_segments[i].ist1 = 0; // ist will created per task
-		task_state_segments[i].ist2 = (size_t) stack_table[i] + (2 /*IST number */ - 1) * KERNEL_STACK_SIZE - 0x10;
-		task_state_segments[i].ist3 = (size_t) stack_table[i] + (3 /*IST number */ - 1) * KERNEL_STACK_SIZE - 0x10;
-		task_state_segments[i].ist4 = (size_t) stack_table[i] + (4 /*IST number */ - 1) * KERNEL_STACK_SIZE - 0x10;
 
 		gdt_set_gate(num+i*2, (unsigned long) (task_state_segments+i), sizeof(tss_t),
 			GDT_FLAG_PRESENT | GDT_FLAG_TSS | GDT_FLAG_RING0, 0);
@@ -160,3 +157,21 @@ void gdt_install(void)
 	/* Flush out the old GDT and install the new changes! */
 	gdt_flush();
 }
+
+void tss_init(void)
+{
+	LOG_INFO("Initialized the task state segments\n");
+
+	for(int i=0; i<MAX_CORES; i++) {
+		if (task_state_segments[i].ist1 == 0)
+			task_state_segments[i].ist1 = (size_t) create_stack(KERNEL_STACK_SIZE) + KERNEL_STACK_SIZE - 0x10;
+		if (task_state_segments[i].ist2 == 0)
+			task_state_segments[i].ist2 = (size_t) create_stack(KERNEL_STACK_SIZE) + KERNEL_STACK_SIZE - 0x10;
+		if (task_state_segments[i].ist2 == 0)
+			task_state_segments[i].ist2 = (size_t) create_stack(KERNEL_STACK_SIZE) + KERNEL_STACK_SIZE - 0x10;
+		if (task_state_segments[i].ist3 == 0)
+			task_state_segments[i].ist3 = (size_t) create_stack(KERNEL_STACK_SIZE) + KERNEL_STACK_SIZE - 0x10;
+		if (task_state_segments[i].ist4 == 0)
+			task_state_segments[i].ist4 = (size_t) create_stack(KERNEL_STACK_SIZE) + KERNEL_STACK_SIZE - 0x10;
+	}
+}
diff --git a/arch/x86/mm/memory.c b/arch/x86/mm/memory.c
index 697c2b6ce..a3402a228 100644
--- a/arch/x86/mm/memory.c
+++ b/arch/x86/mm/memory.c
@@ -361,6 +361,9 @@ int memory_init(void)
 		}
 	}
 
+	// Ok, we are now able to use our memory management => update tss
+	tss_init();
+
 	return ret;
 
 oom: