[V2,1/6] oslib-posix: add helpers for stack alloc and free

Commit Message

Peter Lieven July 4, 2016, 12:31 p.m. UTC

Suggested-by: Peter Maydell <[e-mail]>
Signed-off-by: Peter Lieven <[e-mail]>
---
 include/sysemu/os-posix.h | 23 +++++++++++++++++++++++
 util/oslib-posix.c        | 39 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 62 insertions(+)

Comments

Markus Armbruster July 6, 2016, 8:12 a.m. UTC | #1

Peter Lieven <[e-mail]> writes:

> Suggested-by: Peter Maydell <[e-mail]>
> Signed-off-by: Peter Lieven <[e-mail]>

Please mention the guard page in the commit message.

Richard Henderson July 8, 2016, 5:18 p.m. UTC | #2

On 07/04/2016 05:31 AM, Peter Lieven wrote:
> +void *qemu_alloc_stack(size_t sz)
> +{
> +    void *ptr, *guardpage;
> +    size_t pagesz = getpagesize();
> +
> +    /* avoid stacks smaller than _SC_THREAD_STACK_MIN */
> +    sz = MAX(sz, sysconf(_SC_THREAD_STACK_MIN));
...
> +void qemu_free_stack(void *stack, size_t sz)
> +{
> +    sz = MAX(sz, sysconf(_SC_THREAD_STACK_MIN));

I think the MAX+sysconf expression should be hoisted to a common (static) 
function.  With that,

Reviewed-by: Richard Henderson <[e-mail]>


r~

Patch

diff --git a/include/sysemu/os-posix.h b/include/sysemu/os-posix.h
index 9c7dfdf..7630665 100644
--- a/include/sysemu/os-posix.h
+++ b/include/sysemu/os-posix.h
@@ -60,4 +60,27 @@  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 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..1ce35ef 100644
--- a/util/oslib-posix.c
+++ b/util/oslib-posix.c
@@ -497,3 +497,42 @@  pid_t qemu_fork(Error **errp)
     }
     return pid;
 }
+
+void *qemu_alloc_stack(size_t sz)
+{
+    void *ptr, *guardpage;
+    size_t pagesz = getpagesize();
+
+    /* avoid stacks smaller than _SC_THREAD_STACK_MIN */
+    sz = MAX(sz, sysconf(_SC_THREAD_STACK_MIN));
+    /* assert that the stack size is a multiple of the page size */
+    assert(!(sz % pagesz));
+
+    ptr = mmap(NULL, sz, PROT_READ | PROT_WRITE,
+               MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+    if (ptr == MAP_FAILED) {
+        abort();
+    }
+
+#if defined(HOST_IA64)
+    /* separate register stack */
+    guardpage = ptr + (((sz - pagesz) / 2) & ~pagesz);
+#elif defined(HOST_HPPA)
+    /* stack grows up */
+    guardpage = ptr + sz - pagesz;
+#else
+    /* stack grows down */
+    guardpage = ptr;
+#endif
+    if (mprotect(guardpage, pagesz, PROT_NONE) != 0) {
+        abort();
+    }
+
+    return ptr;
+}
+
+void qemu_free_stack(void *stack, size_t sz)
+{
+    sz = MAX(sz, sysconf(_SC_THREAD_STACK_MIN));
+    munmap(stack, sz);
+}