Changes in kernel/generic/include/context.h [ed7e057:8df5f20] in mainline

File:

• kernel/generic/include/context.h (modified) (3 diffs)

kernel/generic/include/context.h

@@ -36 +36 @@
 #define KERN_CONTEXT_H_
 
-#include <panic.h>
 #include <trace.h>
 #include <arch/context.h>
-#include <arch/faddr.h>
 
 #define context_set_generic(ctx, _pc, stack, size) \
@@ -49 +47 @@
 extern int context_save_arch(context_t *ctx) __attribute__((returns_twice));
 extern void context_restore_arch(context_t *ctx) __attribute__((noreturn));
+
+/** Save register context.
+ *
+ * Save the current register context (including stack pointer) to a context
+ * structure. A subsequent call to context_restore() will return to the same
+ * address as the corresponding call to context_save().
+ *
+ * Note that context_save_arch() must reuse the stack frame of the function
+ * which called context_save(). We guarantee this by:
+ *
+ *   a) implementing context_save_arch() in assembly so that it does not create
+ *      its own stack frame, and by
+ *   b) defining context_save() as a macro because the inline keyword is just a
+ *      hint for the compiler, not a real constraint; the application of a macro
+ *      will definitely not create a stack frame either.
+ *
+ * To imagine what could happen if there were some extra stack frames created
+ * either by context_save() or context_save_arch(), we need to realize that the
+ * sp saved in the contex_t structure points to the current stack frame as it
+ * existed when context_save_arch() was executing. After the return from
+ * context_save_arch() and context_save(), any extra stack frames created by
+ * these functions will be destroyed and their contents sooner or later
+ * overwritten by functions called next. Any attempt to restore to a context
+ * saved like that would therefore lead to a disaster.
+ *
+ * @param ctx Context structure.
+ *
+ * @return context_save() returns 1, context_restore() returns 0.
+ *
+ */
+#define context_save(ctx)  context_save_arch(ctx)
 
 /** Restore register context.
@@ -62 +91 @@
  *
  */
-_NO_TRACE __attribute__((noreturn))
-    static inline void context_restore(context_t *ctx)
+_NO_TRACE static inline void context_restore(context_t *ctx)
 {
         context_restore_arch(ctx);
-}
-
-/**
- * Saves current context to the variable pointed to by `self`,
- * and restores the context denoted by `other`.
- *
- * When the `self` context is later restored by another call to
- * `context_swap()`, the control flow behaves as if the earlier call to
- * `context_swap()` just returned.
- */
-_NO_TRACE static inline void context_swap(context_t *self, context_t *other)
-{
-        if (context_save_arch(self))
-                context_restore_arch(other);
-}
-
-_NO_TRACE static inline void context_create(context_t *context,
-    void (*fn)(void), void *stack_base, size_t stack_size)
-{
-        *context = (context_t) { 0 };
-        context_set(context, FADDR(fn), stack_base, stack_size);
-}
-
-__attribute__((noreturn)) static inline void context_replace(void (*fn)(void),
-    void *stack_base, size_t stack_size)
-{
-        context_t ctx;
-        context_create(&ctx, fn, stack_base, stack_size);
-        context_restore(&ctx);
 }