[cfe-commits] [libcxxabi] r149154 - /libcxxabi/trunk/src/cxa_personality.cpp
Howard Hinnant
hhinnant at apple.com
Fri Jan 27 16:28:31 PST 2012
Author: hhinnant
Date: Fri Jan 27 18:28:31 2012
New Revision: 149154
URL: http://llvm.org/viewvc/llvm-project?rev=149154&view=rev
Log:
Sometimes it takes all day to write a decent comment. This is one of those times, and I'm still not quite sure I have them correct.
Modified:
libcxxabi/trunk/src/cxa_personality.cpp
Modified: libcxxabi/trunk/src/cxa_personality.cpp
URL: http://llvm.org/viewvc/llvm-project/libcxxabi/trunk/src/cxa_personality.cpp?rev=149154&r1=149153&r2=149154&view=diff
==============================================================================
--- libcxxabi/trunk/src/cxa_personality.cpp (original)
+++ libcxxabi/trunk/src/cxa_personality.cpp Fri Jan 27 18:28:31 2012
@@ -19,16 +19,79 @@
#include <stdlib.h>
#include <assert.h>
-// +---------------------------+-----------------------------+---------------+
-// | __cxa_exception | _Unwind_Exception CLNGC++\0 | thrown object |
-// +---------------------------+-----------------------------+---------------+
-// ^
-// |
-// +-------------------------------------------------------+
-// |
-// +---------------------------+-----------------------------+
-// | __cxa_dependent_exception | _Unwind_Exception CLNGC++\1 |
-// +---------------------------+-----------------------------+
+/*
+Exception Header Layout:
+
++---------------------------+-----------------------------+---------------+
+| __cxa_exception | _Unwind_Exception CLNGC++\0 | thrown object |
++---------------------------+-----------------------------+---------------+
+ ^
+ |
+ +-------------------------------------------------------+
+ |
++---------------------------+-----------------------------+
+| __cxa_dependent_exception | _Unwind_Exception CLNGC++\1 |
++---------------------------+-----------------------------+
+
+ Exception Handling Table Layout:
+
++-----------------+--------+
+| lpStartEncoding | (char) |
++---------+-------+--------+---------------+-----------------------+
+| lpStart | (encoded wtih lpStartEncoding) | defaults to funcStart |
++---------+-----+--------+-----------------+---------------+-------+
+| ttypeEncoding | (char) | Encoding of the type_info table |
++---------------+-+------+----+----------------------------+----------------+
+| classInfoOffset | (ULEB128) | Offset to type_info table, defaults to null |
++-----------------++--------+-+----------------------------+----------------+
+| callSiteEncoding | (char) | Encoding for Call Site Table |
++------------------+--+-----+-----+------------------------+--------------------------+
+| callSiteTableLength | (ULEB128) | Call Site Table length, used to find Action table |
++---------------------+-----------+--------------------------------------------------++
+| Beginning of Call Site Table If the current ip lies within the |
+| ... (start, length) range of one of these |
+| call sites, there may be action needed. |
+| +-------------+-----------------------------------+------------------------------+ |
+| | start | (encoded with Call Site Encoding) | offset relative to funcStart | |
+| | length | (encoded with Call Site Encoding) | lenght of code fragment | |
+| | landingPad | (encoded with Call Site Encoding) | offset relative to lpStart | |
+| | actionEntry | (ULEB128) | Action Table Index 1-based | |
+| | | | actionEntry == 0 -> clean up | |
+| +-------------+-----------------------------------+------------------------------+ |
+| ... |
++---------------------------------------------------------------------+--------------+
+| Beginning of Action Table ttypeIndex == 0 : cleanup |
+| ... ttypeIndex > 0 : catch |
+| ttypeIndex < 0 : exception spec |
+| +--------------+-----------+--------------------------------------+ |
+| | ttypeIndex | (SLEB128) | Index into type_info Table (1-based) | |
+| | actionOffset | (SLEB128) | Offset into next Action Table entry | |
+| +--------------+-----------+--------------------------------------+ |
+| ... |
++---------------------------------------------------------------------+-----------------+
+| type_info Table, but classInfoOffset does *not* point here! |
+| +----------------+------------------------------------------------+-----------------+ |
+| | Nth type_info* | Encoded with ttypeEncoding, 0 means every type | ttypeIndex == N | |
+| +----------------+------------------------------------------------+-----------------+ |
+| ... |
+| +----------------+------------------------------------------------+-----------------+ |
+| | 1st type_info* | Encoded with ttypeEncoding, 0 means every type | ttypeIndex == 1 | |
+| +----------------+------------------------------------------------+-----------------+ |
+| +---------------------------------------+-----------+------------------------------+ |
+| | 1st ttypeIndex for 1st exception spec | (ULEB128) | classInfoOffset points here! | |
+| | 2nd ttypeIndex for 1st exception spec | (ULEB128) | | |
+| | 3rd ttypeIndex for 1st exception spec | (ULEB128) | | |
+| | 0 | (ULEB128) | | |
+| +---------------------------------------+------------------------------------------+ |
+| ... |
+| +---------------------------------------+------------------------------------------+ |
+| | 1st ttypeIndex for Nth exception spec | (ULEB128) | | |
+| | 2nd ttypeIndex for Nth exception spec | (ULEB128) | | |
+| | 3rd ttypeIndex for Nth exception spec | (ULEB128) | | |
+| | 0 | (ULEB128) | | |
+| +---------------------------------------+------------------------------------------+ |
++---------------------------------------------------------------------------------------+
+*/
namespace __cxxabiv1
{
@@ -197,27 +260,27 @@
static
const uint8_t*
-getTTypeEntry(int64_t typeOffset, const uint8_t* classInfo, uint8_t ttypeEncoding)
+getTTypeEntry(int64_t ttypeIndex, const uint8_t* classInfo, uint8_t ttypeEncoding)
{
switch (ttypeEncoding & 0x0F)
{
case DW_EH_PE_absptr:
- typeOffset *= sizeof(void*);
+ ttypeIndex *= sizeof(void*);
break;
case DW_EH_PE_udata2:
case DW_EH_PE_sdata2:
- typeOffset *= 2;
+ ttypeIndex *= 2;
break;
case DW_EH_PE_udata4:
case DW_EH_PE_sdata4:
- typeOffset *= 4;
+ ttypeIndex *= 4;
break;
case DW_EH_PE_udata8:
case DW_EH_PE_sdata8:
- typeOffset *= 8;
+ ttypeIndex *= 8;
break;
}
- return classInfo - typeOffset;
+ return classInfo - ttypeIndex;
}
/// Deals with Dwarf actions matching our type infos
@@ -254,12 +317,12 @@
// type info address offset, and action offset to the next
// emitted action.
const uint8_t* SactionPos = actionPos;
- int64_t typeOffset = readSLEB128(&actionPos);
+ int64_t ttypeIndex = readSLEB128(&actionPos);
const uint8_t* tempActionPos = actionPos;
int64_t actionOffset = readSLEB128(&tempActionPos);
- if (typeOffset > 0) // a catch handler
+ if (ttypeIndex > 0) // a catch handler
{
- const uint8_t* TTypeEntry = getTTypeEntry(typeOffset, classInfo,
+ const uint8_t* TTypeEntry = getTTypeEntry(ttypeIndex, classInfo,
ttypeEncoding);
const __shim_type_info* catchType =
(const __shim_type_info*)readEncodedPointer(&TTypeEntry,
@@ -268,17 +331,17 @@
// catchType == 0 -> catch (...)
if (catchType == 0 || catchType->can_catch(excpType, adjustedPtr))
{
- exception_header->handlerSwitchValue = typeOffset;
+ exception_header->handlerSwitchValue = ttypeIndex;
exception_header->actionRecord = SactionPos; // unnecessary?
// used by __cxa_get_exception_ptr and __cxa_begin_catch
exception_header->adjustedPtr = adjustedPtr;
return true;
}
}
- else if (typeOffset < 0) // an exception spec
+ else if (ttypeIndex < 0) // an exception spec
{
}
- else // typeOffset == 0 // a clean up
+ else // ttypeIndex == 0 // a clean up
{
}
if (actionOffset == 0)
@@ -302,18 +365,19 @@
{
// Get the current instruction pointer and offset it before next
// instruction in the current frame which threw the exception.
- uintptr_t pc = _Unwind_GetIP(context) - 1;
+ uintptr_t ip = _Unwind_GetIP(context) - 1;
// Get beginning current frame's code (as defined by the
// emitted dwarf code)
uintptr_t funcStart = _Unwind_GetRegionStart(context);
- uintptr_t pcOffset = pc - funcStart;
+ uintptr_t ipOffset = ip - funcStart;
const uint8_t* classInfo = NULL;
// Note: See JITDwarfEmitter::EmitExceptionTable(...) for corresponding
// dwarf emission
// Parse LSDA header.
uint8_t lpStartEncoding = *lsda++;
- if (lpStartEncoding != DW_EH_PE_omit)
- (void)readEncodedPointer(&lsda, lpStartEncoding);
+ const uint8_t* lpStart = (const unit8_t*)readEncodedPointer(&lsda, lpStartEncoding);
+ if (lpStart == 0)
+ lpStart = funcStart;
uint8_t ttypeEncoding = *lsda++;
// TODO: preflight ttypeEncoding here and return error if there's a problem
if (ttypeEncoding != DW_EH_PE_omit)
@@ -343,9 +407,9 @@
continue; // no landing pad for this entry
if (actionEntry)
actionEntry += ((uintptr_t)actionTableStart) - 1;
- if ((start <= pcOffset) && (pcOffset < (start + length)))
+ if ((start <= ipOffset) && (ipOffset < (start + length)))
{
- exception_header->catchTemp = (void*)(funcStart + landingPad);
+ exception_header->catchTemp = (void*)(lpStart + landingPad);
if (actionEntry)
return handleActionValue(classInfo,
actionEntry,
@@ -355,7 +419,7 @@
// found. Otherwise the clean up handlers will be
// re-found and executed during the clean up
// phase.
- return true; //?
+ return false; // Won't find another call site in range of ipOffset
}
}
// Not found, need to properly terminate
@@ -388,13 +452,57 @@
// public API
-// Requires: version == 1
-// actions == _UA_SEARCH_PHASE, or
-// == _UA_CLEANUP_PHASE, or
-// == _UA_CLEANUP_PHASE | _UA_HANDLER_FRAME, or
-// == _UA_CLEANUP_PHASE | _UA_FORCE_UNWIND
-// unwind_exception != nullptr
-// context != nullptr
+/*
+A foreign exception is defined by by one with an exceptionClass that doesn't
+have 'C++' in the 3 low order bytes 3 - 1:
+
+ big end | | ... | C | + | + |1/0| little end
+
+The lowest order byte may be 0 or 1.
+
+The personality function branches on actions like so:
+
+_UA_SEARCH_PHASE
+
+ If _UA_CLEANUP_PHASE or _UA_HANDLER_FRAME or _UA_FORCE_UNWIND there's
+ an error from above, return _URC_FATAL_PHASE1_ERROR.
+
+ Scan for anything that could stop unwinding:
+
+ 1. A catch clause that will catch this exception
+ (will never catch foreign).
+ 2. A catch (...) (will always catch foreign).
+ 3. An exception spec that will catch this exception
+ (will always catch foreign).
+ If a handler is found
+ If not foreign
+ Save state in header
+ return _URC_HANDLER_FOUND
+ Else a handler not found
+ return _URC_CONTINUE_UNWIND
+
+_UA_CLEANUP_PHASE
+
+ If _UA_HANDLER_FRAME
+ If _UA_FORCE_UNWIND
+ How did this happen? return _URC_FATAL_PHASE2_ERROR
+ If foreign
+ Do _UA_SEARCH_PHASE to recover state
+ else
+ Recover state from header
+ Transfer control to landing pad. return _URC_INSTALL_CONTEXT
+
+ Else
+
+ Scan for anything that can not stop unwinding:
+
+ 1. A clean up.
+
+ If a clean up is found
+ transfer control to it. return _URC_INSTALL_CONTEXT
+
+ Else a clean up is not found: return _URC_CONTINUE_UNWIND
+*/
_Unwind_Reason_Code
__gxx_personality_v0(int version, _Unwind_Action actions, uint64_t exceptionClass,
_Unwind_Exception* unwind_exception, _Unwind_Context* context)
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