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Diffstat (limited to 'docs/ExceptionHandling.rst')
| -rw-r--r-- | docs/ExceptionHandling.rst | 65 |
1 files changed, 59 insertions, 6 deletions
diff --git a/docs/ExceptionHandling.rst b/docs/ExceptionHandling.rst index 696b50f..21de19b 100644 --- a/docs/ExceptionHandling.rst +++ b/docs/ExceptionHandling.rst @@ -442,7 +442,7 @@ Uses of this intrinsic are generated by the C++ front-end. .. code-block:: llvm - i8* @llvm.eh.begincatch(i8* %exn) + void @llvm.eh.begincatch(i8* %ehptr, i8* %ehobj) This intrinsic marks the beginning of catch handling code within the blocks @@ -450,11 +450,11 @@ following a ``landingpad`` instruction. The exact behavior of this function depends on the compilation target and the personality function associated with the ``landingpad`` instruction. -The argument to this intrinsic is a pointer that was previously extracted from -the aggregate return value of the ``landingpad`` instruction. The return -value of the intrinsic is a pointer to the exception object to be used by the -catch code. This pointer is returned as an ``i8*`` value, but the actual type -of the object will depend on the exception that was thrown. +The first argument to this intrinsic is a pointer that was previously extracted +from the aggregate return value of the ``landingpad`` instruction. The second +argument to the intrinsic is a pointer to stack space where the exception object +should be stored. The runtime handles the details of copying the exception +object into the slot. If the second parameter is null, no copy occurs. Uses of this intrinsic are generated by the C++ front-end. Many targets will use implementation-specific functions (such as ``__cxa_begin_catch``) instead @@ -498,6 +498,59 @@ When used in the native Windows C++ exception handling implementation, this intrinsic serves as a placeholder to delimit code before a catch handler is outlined. After the handler is outlined, this intrinsic is simply removed. +.. _llvm.eh.actions: + +``llvm.eh.actions`` +---------------------- + +.. code-block:: llvm + + void @llvm.eh.actions() + +This intrinsic represents the list of actions to take when an exception is +thrown. It is typically used by Windows exception handling schemes where cleanup +outlining is required by the runtime. The arguments are a sequence of ``i32`` +sentinels indicating the action type followed by some pre-determined number of +arguments required to implement that action. + +A code of ``i32 0`` indicates a cleanup action, which expects one additional +argument. The argument is a pointer to a function that implements the cleanup +action. + +A code of ``i32 1`` indicates a catch action, which expects three additional +arguments. Different EH schemes give different meanings to the three arguments, +but the first argument indicates whether the catch should fire, the second is a +pointer to stack object where the exception object should be stored, and the +third is the code to run to catch the exception. + +For Windows C++ exception handling, the first argument for a catch handler is a +pointer to the RTTI type descriptor for the object to catch. The third argument +is a pointer to a function implementing the catch. This function returns the +address of the basic block where execution should resume after handling the +exception. + +For Windows SEH, the first argument is a pointer to the filter function, which +indicates if the exception should be caught or not. The second argument is +typically null. The third argument is the address of a basic block where the +exception will be handled. In other words, catch handlers are not outlined in +SEH. After running cleanups, execution immediately resumes at this PC. + +In order to preserve the structure of the CFG, a call to '``llvm.eh.actions``' +must be followed by an ':ref:`indirectbr <i_indirectbr>`' instruction that jumps +to the result of the intrinsic call. + +``llvm.eh.unwindhelp`` +---------------------- + +.. code-block:: llvm + + void @llvm.eh.unwindhelp(i8*) + +This intrinsic designates the provided static alloca as the unwind help object. +This object is used by Windows native exception handling on non-x86 platforms +where xdata unwind information is used. It is typically an 8 byte chunk of +memory treated as two 32-bit integers. + SJLJ Intrinsics --------------- |