From cadacc24aed06c1a90af5e8d693c7726049f4b50 Mon Sep 17 00:00:00 2001
From: Stefan Lankes <slankes@eonerc.rwth-aachen.de>
Date: Sun, 27 Nov 2016 23:21:47 +0100
Subject: [PATCH] reserve at boot time a region for the heap

=> no race between stack und heap creation
---
 include/hermit/config.h |  3 ++-
 kernel/main.c           |  5 ++++-
 kernel/syscall.c        | 23 +++++++++++++++++++----
 mm/vma.c                |  6 ++++++
 4 files changed, 31 insertions(+), 6 deletions(-)

diff --git a/include/hermit/config.h b/include/hermit/config.h
index 2e103436f..82a1862d6 100644
--- a/include/hermit/config.h
+++ b/include/hermit/config.h
@@ -42,7 +42,8 @@ extern "C" {
 #define CACHE_LINE		64
 #define KERNEL_STACK_SIZE	(8*1024)
 #define DEFAULT_STACK_SIZE	(256*1024)
-#define HEAP_START		(1ULL << 34)
+#define HEAP_START		(PAGE_2M_FLOOR((size_t)&kernel_end) + 4*PAGE_SIZE)
+#define HEAP_SIZE		(1ULL << 32)
 #define KMSG_SIZE		(4*1024)
 #define INT_SYSCALL		0x80
 #define MAILBOX_SIZE		128
diff --git a/kernel/main.c b/kernel/main.c
index 221c7c04a..f268ef8d6 100644
--- a/kernel/main.c
+++ b/kernel/main.c
@@ -392,7 +392,9 @@ static int initd(void* arg)
 	curr_task->heap->start = PAGE_FLOOR(heap);
 	curr_task->heap->end = PAGE_FLOOR(heap);
 
-	// reserve VMA region
+	// region is already reserved for the heap, we have to change the
+	// property of the first page
+	vma_free(curr_task->heap->start, curr_task->heap->start+PAGE_SIZE);
 	vma_add(curr_task->heap->start, curr_task->heap->start+PAGE_SIZE, VMA_HEAP|VMA_USER);
 
 	//create_kernel_task(NULL, foo, "foo1", NORMAL_PRIO);
@@ -595,6 +597,7 @@ int hermit_main(void)
 		PAUSE;
 
 	print_status();
+	//vma_dump();
 
 	create_kernel_task_on_core(NULL, initd, NULL, NORMAL_PRIO, boot_processor);
 
diff --git a/kernel/syscall.c b/kernel/syscall.c
index f738cb264..daf7c5ff9 100644
--- a/kernel/syscall.c
+++ b/kernel/syscall.c
@@ -43,6 +43,13 @@
 #include <lwip/err.h>
 #include <lwip/stats.h>
 
+/*
+ * 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 kernel_start;
+extern const void kernel_end;
+
 //TODO: don't use one big kernel lock to comminicate with all proxies
 static spinlock_irqsave_t lwip_lock = SPINLOCK_IRQSAVE_INIT;
 
@@ -244,11 +251,19 @@ ssize_t sys_sbrk(ssize_t incr)
 	spinlock_lock(&heap_lock);
 
 	ret = heap->end;
-	heap->end += incr;
 
-	// reserve VMA regions
-	if (PAGE_CEIL(heap->end) > PAGE_CEIL(ret))
-		vma_add(PAGE_CEIL(ret), PAGE_FLOOR(heap->end), VMA_HEAP|VMA_USER);
+	// check heapp boundaries
+	if ((heap->end >= HEAP_START) && (heap->end+incr < HEAP_START + HEAP_SIZE)) {
+		heap->end += incr;
+
+		// reserve VMA regions
+		if (PAGE_CEIL(heap->end) > PAGE_CEIL(ret)) {
+			// region is already reserved for the heap, we have to change the
+			// property
+			vma_free(PAGE_CEIL(ret), PAGE_FLOOR(heap->end));
+			vma_add(PAGE_CEIL(ret), PAGE_FLOOR(heap->end), VMA_HEAP|VMA_USER);
+		}
+	} else ret = -ENOMEM;
 
 	// allocation and mapping of new pages for the heap
 	// is catched by the pagefault handler
diff --git a/mm/vma.c b/mm/vma.c
index c1652794a..435ba0977 100644
--- a/mm/vma.c
+++ b/mm/vma.c
@@ -68,6 +68,11 @@ int vma_init(void)
 	if (BUILTIN_EXPECT(ret, 0))
 		goto out;
 
+	// reserve space for the heap
+	ret = vma_add(HEAP_START, HEAP_START+HEAP_SIZE, VMA_NO_ACCESS);
+	if (BUILTIN_EXPECT(ret, 0))
+		goto out;
+
 #ifdef CONFIG_VGA
 	// add VGA video memory
 	ret = vma_add(VIDEO_MEM_ADDR, VIDEO_MEM_ADDR + PAGE_SIZE, VMA_READ|VMA_WRITE);
@@ -141,6 +146,7 @@ found:
 		new->flags = flags;
 		new->next = succ;
 		new->prev = pred;
+		LOG_DEBUG("vma_alloc: create new vma, new->start 0x%zx, new->end 0x%zx\n", new->start, new->end);
 
 		if (succ)
 			succ->prev = new;