[Qemu-devel] [PATCH 1/6] oslib-posix: add helpers for stack alloc and free

[Peter Lieven]

Suggested-by: Peter Maydell <address@hidden>
Signed-off-by: Peter Lieven <address@hidden>
---
 include/sysemu/os-posix.h | 24 ++++++++++++++++++++++++
 util/oslib-posix.c        | 22 ++++++++++++++++++++++
 2 files changed, 46 insertions(+)

diff --git a/include/sysemu/os-posix.h b/include/sysemu/os-posix.h
index 9c7dfdf..34d102c 100644
--- a/include/sysemu/os-posix.h
+++ b/include/sysemu/os-posix.h
@@ -60,4 +60,28 @@ int qemu_utimens(const char *path, const qemu_timespec 
*times);
 
 bool is_daemonized(void);
 
+/**
+ * qemu_alloc_stack:
+ * @sz: size of required stack in bytes
+ *
+ * Allocate memory that can be used as a stack, for instance for
+ * coroutines. If the memory cannot be allocated, this function
+ * will abort (like g_malloc()). The function will register a
+ * guard page right below the stack memory to catch stack overflows.
+ *
+ * The allocated stack must be freed with qemu_free_stack().
+ *
+ * Returns: pointer to (the lowest address of) the stack memory.
+ */
+void *qemu_alloc_stack(size_t sz);
+
+/**
+ * qemu_free_stack:
+ * @stack: stack to free
+ * @sz: size of stack in bytes
+ *
+ * Free a stack allocated via qemu_alloc_stack().
+ */
+void qemu_free_stack(void *stack, size_t sz);
+
 #endif
diff --git a/util/oslib-posix.c b/util/oslib-posix.c
index e2e1d4d..a567a7d 100644
--- a/util/oslib-posix.c
+++ b/util/oslib-posix.c
@@ -497,3 +497,25 @@ pid_t qemu_fork(Error **errp)
     }
     return pid;
 }
+
+void *qemu_alloc_stack(size_t sz)
+{
+    /* allocate sz bytes plus one extra page for a guard
+     * page at the bottom of the stack */
+    void *ptr = mmap(NULL, sz + getpagesize(), PROT_NONE,
+                     MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+    if (ptr == MAP_FAILED) {
+        abort();
+    }
+    if (mmap(ptr + getpagesize(), sz, PROT_READ | PROT_WRITE,
+        MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED, -1, 0) == MAP_FAILED) {
+        abort();
+    }
+    return ptr + getpagesize();
+}
+
+void qemu_free_stack(void *stack, size_t sz)
+{
+    /* unmap the stack plus the extra guard page */
+    munmap(stack - getpagesize(), sz + getpagesize());
+}
-- 
1.9.1