diff mbox series

[1/2] libio: Introduce _IO_JUMPS_UNVALIDATED

Message ID cf56a61681926b77d13046526ff01e705fefbbfe.1691499154.git.fweimer@redhat.com
State New
Headers
Series [1/2] libio: Introduce _IO_JUMPS_UNVALIDATED |

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Commit Message

Florian Weimer Aug. 8, 2023, 12:53 p.m. UTC 
  And refactor the macros a bit.  Use a safer way to avoid aliasing
issues.
---
 libio/libioP.h | 40 ++++++++++++++++++++++++++++++----------
 1 file changed, 30 insertions(+), 10 deletions(-)


base-commit: dcad5c8578130dec7f35fd5b0885304b59f9f543
diff mbox series

Patch

diff --git a/libio/libioP.h b/libio/libioP.h
index 745278e076..0c5276fc4b 100644
--- a/libio/libioP.h
+++ b/libio/libioP.h
@@ -104,21 +104,41 @@ 
 #define _IO_CHECK_WIDE(THIS) \
   (_IO_CAST_FIELD_ACCESS ((THIS), struct _IO_FILE, _wide_data) != NULL)
 
+
 #if _IO_JUMPS_OFFSET
-# define _IO_JUMPS_FUNC(THIS) \
-  (IO_validate_vtable                                                   \
-   (*(struct _IO_jump_t **) ((void *) &_IO_JUMPS_FILE_plus (THIS)	\
-			     + (THIS)->_vtable_offset)))
-# define _IO_JUMPS_FUNC_UPDATE(THIS, VTABLE)				\
-  (*(const struct _IO_jump_t **) ((void *) &_IO_JUMPS_FILE_plus (THIS)	\
-				  + (THIS)->_vtable_offset) = (VTABLE))
 # define _IO_vtable_offset(THIS) (THIS)->_vtable_offset
 #else
-# define _IO_JUMPS_FUNC(THIS) (IO_validate_vtable (_IO_JUMPS_FILE_plus (THIS)))
-# define _IO_JUMPS_FUNC_UPDATE(THIS, VTABLE) \
-  (_IO_JUMPS_FILE_plus (THIS) = (VTABLE))
 # define _IO_vtable_offset(THIS) 0
 #endif
+
+/* Pointer to the active vtable pointer in a FILE object.  */
+#define _IO_vtable_ptrptr(THIS) \
+  ((void *) &_IO_JUMPS_FILE_plus (THIS) + _IO_vtable_offset (THIS))
+
+/* Read the vtable pointer in THIS, avoiding an aliasing violation.
+   This performs no vtable validation, so should only be used for
+   explicit checks against known vtables.  */
+#define _IO_JUMPS_UNVALIDATED(THIS)				\
+  ({								\
+    struct _IO_jump_t *__jump_unvalidated;			\
+    memcpy (&__jump_unvalidated, _IO_vtable_ptrptr (THIS),	\
+	    sizeof (__jump_unvalidated));			\
+    __jump_unvalidated;						\
+  })
+
+/* Like _IO_JUMPS_UNVALIDATED, but with validation.  Used to implement
+   virtual member function calls below.  */
+#define _IO_JUMPS_FUNC(THIS) \
+  (IO_validate_vtable (_IO_JUMPS_UNVALIDATED (THIS)))
+
+/* Update the vtable pointer, avoiding an aliasing violation.  */
+#define _IO_JUMPS_FUNC_UPDATE(THIS, VTABLE)                             \
+  ({                                                                    \
+    const struct _IO_jump_t *__jump_copy = (VTABLE);                    \
+    memcpy (_IO_vtable_ptrptr (THIS), &__jump_copy, sizeof (__jump_copy)); \
+    (void) 0;                                                           \
+  })
+
 #define _IO_WIDE_JUMPS_FUNC(THIS) _IO_WIDE_JUMPS(THIS)
 #define JUMP_FIELD(TYPE, NAME) TYPE NAME
 #define JUMP0(FUNC, THIS) (_IO_JUMPS_FUNC(THIS)->FUNC) (THIS)