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Minor tidying and improved documentation in the leader comment.
Copied from Perforce Change: 182924 ServerID: perforce.ravenbrook.com
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Richard Brooksby
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1 changed files with 60 additions and 22 deletions
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@ -3,18 +3,51 @@
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* $Id$
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* Copyright (c) 2013 Ravenbrook Limited. See end of file for license.
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*
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* SOURCES
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* This is the protection exception handling code for Mac OS X using the
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* Mach interface (not pthreads).
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*
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* In Mach, a thread that hits protected memory is suspended, and a message
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* is sent to a separate handler thread.
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* The handler thread can fix things up and continue the suspended thread by
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* sending back a "success" reply. It can forward the message to another
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* handler of the same kind, or it can forward the message to another handler
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* at the next level out (the levels are thread, task, host) by sending a
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* "fail" reply.
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*
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* In Mac OS X, pthreads are implemented by Mach threads. (The implementation
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* is part of the XNU source code at opensource.apple.com. [copy to import?])
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* So we can use some pthread interfaces for convenience in setting up threads.
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*
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* This module sets up an exception handling thread for the EXC_BAD_ACCESS
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* exceptions that will be caused by the MPS shield (read/write barriers).
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* That thread calls the MPS to resolve the condition and allow the mutator
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* thread to progress.
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*
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* That part is fairly simple. Most of the code in this module is concerned
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* with decoding Mach messages and re-encoding them in order to forward them
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* on to other exception handlers.
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*
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*
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* SOURCES
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* .source.man: <http://felinemenace.org/~nemo/mach/manpages/>
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* <http://web.mit.edu/darwin/src/modules/xnu/osfmk/man/>
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*
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*
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* REFERENCES
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* http://www.mikeash.com/pyblog/friday-qa-2013-01-11-mach-exception-handlers.html
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* [Fuller_2013] "Mach Exception Handlers"; Landon Fuller;
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* <http://www.mikeash.com/pyblog/friday-qa-2013-01-11-mach-exception-handlers.html>
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*
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*
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* TRANSGRESSIONS
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*
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* .trans.stdlib: It's OK to use the C library from here because we know
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* we're on OS X and not freestanding. In particular, we use memcpy.
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*/
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#include "mpm.h"
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#include "prmcxc.h"
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#include <stdlib.h>
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#include <stdlib.h> /* see .trans.stdlib */
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#include <pthread.h>
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@ -101,6 +134,8 @@ typedef REQUEST_RAISE_STATE_STRUCT(request_s64_s, __int64_t) request_s64_s;
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typedef REQUEST_RAISE_STATE_IDENTITY_STRUCT(request_si32_s, __int32_t) request_si32_s;
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typedef REQUEST_RAISE_STATE_IDENTITY_STRUCT(request_si64_s, __int64_t) request_si64_s;
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typedef __Reply__exception_raise_state_identity_t reply_si_s;
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#ifdef __MigPackStructs
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#pragma pack()
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#endif
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@ -125,7 +160,7 @@ typedef REQUEST_RAISE_STATE_IDENTITY_STRUCT(request_si64_s, __int64_t) request_s
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Mac OS X does. */
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#define COPY_COMMON(dst, src, id, code_type) \
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do { \
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BEGIN \
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(dst)->Head = (src)->Head; \
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(dst)->Head.msgh_id = (id); \
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(dst)->Head.msgh_size = sizeof(*dst); \
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@ -134,16 +169,16 @@ typedef REQUEST_RAISE_STATE_IDENTITY_STRUCT(request_si64_s, __int64_t) request_s
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(dst)->codeCnt = (src)->codeCnt; \
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(dst)->code[0] = (code_type)(src)->code[0]; \
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(dst)->code[1] = (code_type)(src)->code[1]; \
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} while(0)
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END
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#define COPY_IDENTITY(dst, src) \
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do { \
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BEGIN \
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(dst)->thread = (src)->thread; \
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(dst)->task = (src)->task; \
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} while(0)
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END
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#define COPY_STATE(dst, src, state_flavor, state, state_count) \
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do { \
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BEGIN \
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mach_msg_size_t _s; \
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(dst)->flavor = (state_flavor); \
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(dst)->old_stateCnt = (state_count); \
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@ -152,26 +187,26 @@ typedef REQUEST_RAISE_STATE_IDENTITY_STRUCT(request_si64_s, __int64_t) request_s
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memcpy((dst)->old_state, (state), _s); \
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(dst)->Head.msgh_size = \
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offsetof(request_s32_s, old_state) + _s; \
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} while(0)
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END
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#define COPY_REQUEST(dst, src, width) \
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do { \
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BEGIN \
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COPY_COMMON(dst, src, MSG_ID_REQUEST_##width, __int##width##_t); \
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COPY_IDENTITY(dst, src); \
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} while(0);
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END;
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#define COPY_REQUEST_STATE(dst, src, width, state_flavor, state, state_count) \
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do { \
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BEGIN \
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COPY_COMMON(dst, src, MSG_ID_REQUEST_STATE_##width, __int##width##_t); \
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COPY_STATE(dst, src, state_flavor, state, state_count); \
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} while(0)
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END
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#define COPY_REQUEST_STATE_IDENTITY(dst, src, width, state_flavor, state, state_count) \
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do { \
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BEGIN \
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COPY_COMMON(dst, src, MSG_ID_REQUEST_STATE_IDENTITY_##width, __int##width##_t); \
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COPY_IDENTITY(dst, src); \
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COPY_STATE(dst, src, state_flavor, state, state_count); \
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} while(0)
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END
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/* Guard used to ensure we only set up the exception handler once. */
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@ -231,7 +266,7 @@ static int catch_bad_access(void *address, THREAD_STATE_T *state)
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/* Build a reply message based on a request. */
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static void build_reply(__Reply__exception_raise_state_identity_t *reply,
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static void build_reply(reply_si_s *reply,
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request_si64_s *request,
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kern_return_t ret_code)
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{
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@ -250,7 +285,7 @@ static void build_reply(__Reply__exception_raise_state_identity_t *reply,
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memcpy(reply->new_state, request->old_state, state_size);
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/* If you use sizeof(reply) for reply->Head.msgh_size then the state
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gets ignored. */
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reply->Head.msgh_size = offsetof(__Reply__exception_raise_state_identity_t, new_state) + state_size;
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reply->Head.msgh_size = offsetof(reply_si_s, new_state) + state_size;
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}
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@ -309,7 +344,7 @@ static void handle_one(void)
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kern_return_t kr;
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thread_state_data_t thread_state;
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mach_msg_type_number_t thread_state_count;
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__Reply__exception_raise_state_identity_t reply;
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reply_si_s reply;
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/* TODO: This timeout loop probably isn't necessary, but it might help
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with killing or interrupting the process. */
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@ -354,7 +389,8 @@ static void handle_one(void)
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/* If there was no previously installed exception port, send a reply
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that will cause the system to pass the message on to the next kind
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of handler -- presumably the host handler. */
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of handler -- presumably the host handler. The BSD subsystem of OS X
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has a host handler that turns exception into Unix signals [ref?] */
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if (old_port == MACH_PORT_NULL) {
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build_reply(&reply, &request, KERN_FAILURE);
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@ -362,9 +398,11 @@ static void handle_one(void)
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}
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/* Forward the exception message to the previously installed exception
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port. That port might've been expecting a different behavior and
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flavour, unfortunately, so we have to cope. Note that we leave the
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reply port intact, so we don't have to handle and forward replies. */
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port. This is a common situation when running under a debugger, when
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the port will be the debugger's handler for this process' exceptions.
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Unfortunately, that port might've been expecting a different behavior
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and flavour, so we have to cope. Note that we leave the reply port
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intact, so we don't have to handle and forward replies. */
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switch (old_behaviour) {
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case EXCEPTION_DEFAULT:
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