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Move parts of emscripten exception handling to native code. NFC #16627

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Merged
merged 5 commits into from
Apr 11, 2023
Merged

Move parts of emscripten exception handling to native code. NFC #16627

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fbe49e1
Move parts of emscripten exception handling to native code. NFC
sbc100 Feb 23, 2022
45117ad
Rebaseline test_metadce_cxx_mangle.exports
RReverser Mar 27, 2023
9e0f9a1
Few fixups
RReverser Mar 28, 2023
6dcc5ba
Use -fexceptions for test_rust_gxx_personality_v0
RReverser Mar 28, 2023
ad91df7
Revert some parts
RReverser Mar 29, 2023
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7 changes: 7 additions & 0 deletions emcc.py
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Original file line number Diff line number Diff line change
Expand Up @@ -2785,6 +2785,13 @@ def check_memory_setting(setting):
'__cxa_is_pointer_type',
'__cxa_can_catch',

# __cxa_begin_catch depends on this but we can't use deps info in this
# case because that only works for user-level code, and __cxa_begin_catch
# can be used by the standard library.
'__cxa_increment_exception_refcount',
# Same for __cxa_end_catch
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Also had to add __cxa_decrement_exception_refcount here to make some tests pass; I'm not sure why it wasn't necessary for the original PR but became now - maybe I'm missing a better place where it should be added, or maybe something changed in tests.

'__cxa_decrement_exception_refcount',

# Emscripten exception handling can generate invoke calls, and they call
# setThrew(). We cannot handle this using deps_info as the invokes are not
# emitted because of library function usage, but by codegen itself.
Expand Down
98 changes: 11 additions & 87 deletions src/library_exceptions.js
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Original file line number Diff line number Diff line change
Expand Up @@ -23,11 +23,9 @@ var LibraryExceptions = {
//
// excPtr - Thrown object pointer to wrap. Metadata pointer is calculated from it.
$ExceptionInfo__docs: '/** @constructor */',
$ExceptionInfo__deps: ['__cxa_is_pointer_type',
#if EXCEPTION_DEBUG
'$ptrToString',
$ExceptionInfo__deps: ['$ptrToString'],
#endif
],
$ExceptionInfo: function(excPtr) {
this.excPtr = excPtr;
this.ptr = excPtr - {{{ C_STRUCTS.__cxa_exception.__size__ }}};
Expand All @@ -48,10 +46,6 @@ var LibraryExceptions = {
return {{{ makeGetValue('this.ptr', C_STRUCTS.__cxa_exception.exceptionDestructor, '*') }}};
};

this.set_refcount = function(refcount) {
{{{ makeSetValue('this.ptr', C_STRUCTS.__cxa_exception.referenceCount, 'refcount', 'i32') }}};
};

this.set_caught = function (caught) {
caught = caught ? 1 : 0;
{{{ makeSetValue('this.ptr', C_STRUCTS.__cxa_exception.caught, 'caught', 'i8') }}};
Expand All @@ -78,34 +72,8 @@ var LibraryExceptions = {
this.set_adjusted_ptr(0);
this.set_type(type);
this.set_destructor(destructor);
this.set_refcount(0);
this.set_caught(false);
this.set_rethrown(false);
}

this.add_ref = function() {
#if SHARED_MEMORY
Atomics.add(HEAP32, (this.ptr + {{{ C_STRUCTS.__cxa_exception.referenceCount }}}) >> 2, 1);
#else
var value = {{{ makeGetValue('this.ptr', C_STRUCTS.__cxa_exception.referenceCount, 'i32') }}};
{{{ makeSetValue('this.ptr', C_STRUCTS.__cxa_exception.referenceCount, 'value + 1', 'i32') }}};
#endif
};

// Returns true if last reference released.
this.release_ref = function() {
#if SHARED_MEMORY
var prev = Atomics.sub(HEAP32, (this.ptr + {{{ C_STRUCTS.__cxa_exception.referenceCount }}}) >> 2, 1);
#else
var prev = {{{ makeGetValue('this.ptr', C_STRUCTS.__cxa_exception.referenceCount, 'i32') }}};
{{{ makeSetValue('this.ptr', C_STRUCTS.__cxa_exception.referenceCount, 'prev - 1', 'i32') }}};
#endif
#if ASSERTIONS
assert(prev > 0);
#endif
return prev === 1;
};

this.set_adjusted_ptr = function(adjustedPtr) {
{{{ makeSetValue('this.ptr', C_STRUCTS.__cxa_exception.adjustedPtr, 'adjustedPtr', '*') }}};
};
Expand All @@ -131,52 +99,6 @@ var LibraryExceptions = {
};
},

$exception_addRef: function (info) {
#if EXCEPTION_DEBUG
dbg('exception_addRef ' + ptrToString(info.excPtr));
#endif
info.add_ref();
},

$exception_decRef__deps: ['__cxa_free_exception'
#if EXCEPTION_DEBUG
, '$exceptionLast', '$exceptionCaught'
#endif
],
$exception_decRef: function(info) {
#if EXCEPTION_DEBUG
dbg('exception_decRef ' + ptrToString(info.excPtr));
#endif
// A rethrown exception can reach refcount 0; it must not be discarded
// Its next handler will clear the rethrown flag and addRef it, prior to
// final decRef and destruction here
if (info.release_ref() && !info.get_rethrown()) {
var destructor = info.get_destructor();
if (destructor) {
// In Wasm, destructors return 'this' as in ARM
{{{ makeDynCall('pp', 'destructor') }}}(info.excPtr);
}
___cxa_free_exception(info.excPtr);
#if EXCEPTION_DEBUG
dbg('decref freeing exception ' + [ptrToString(info.excPtr), exceptionLast, 'stack', exceptionCaught]);
#endif
}
},

__cxa_increment_exception_refcount__deps: ['$exception_addRef', '$ExceptionInfo'],
__cxa_increment_exception_refcount__sig: 'vp',
__cxa_increment_exception_refcount: function(ptr) {
if (!ptr) return;
exception_addRef(new ExceptionInfo(ptr));
},

__cxa_decrement_exception_refcount__deps: ['$exception_decRef', '$ExceptionInfo'],
__cxa_decrement_exception_refcount__sig: 'vp',
__cxa_decrement_exception_refcount: function(ptr) {
if (!ptr) return;
exception_decRef(new ExceptionInfo(ptr));
},

// Here, we throw an exception after recording a couple of values that we need to remember
// We also remember that it was the last exception thrown as we need to know that later.
__cxa_throw__sig: 'vppp',
Expand Down Expand Up @@ -224,7 +146,8 @@ var LibraryExceptions = {
return type;
},

__cxa_begin_catch__deps: ['$exceptionCaught', '$exception_addRef', '$uncaughtExceptionCount'],
__cxa_begin_catch__deps: ['$exceptionCaught', '__cxa_increment_exception_refcount',
'$uncaughtExceptionCount'],
__cxa_begin_catch__sig: 'pp',
__cxa_begin_catch: function(ptr) {
var info = new ExceptionInfo(ptr);
Expand All @@ -237,15 +160,15 @@ var LibraryExceptions = {
#if EXCEPTION_DEBUG
dbg('__cxa_begin_catch ' + [ptrToString(ptr), 'stack', exceptionCaught]);
#endif
exception_addRef(info);
___cxa_increment_exception_refcount(info.excPtr);
return info.get_exception_ptr();
},

// We're done with a catch. Now, we can run the destructor if there is one
// and free the exception. Note that if the dynCall on the destructor fails
// due to calling apply on undefined, that means that the destructor is
// an invalid index into the FUNCTION_TABLE, so something has gone wrong.
__cxa_end_catch__deps: ['$exceptionCaught', '$exceptionLast', '$exception_decRef'],
__cxa_end_catch__deps: ['$exceptionCaught', '$exceptionLast', '__cxa_decrement_exception_refcount', 'setThrew'],
__cxa_end_catch__sig: 'v',
__cxa_end_catch: function() {
// Clear state flag.
Expand All @@ -259,17 +182,18 @@ var LibraryExceptions = {
#if EXCEPTION_DEBUG
dbg('__cxa_end_catch popped ' + [info, exceptionLast, 'stack', exceptionCaught]);
#endif
exception_decRef(info);
___cxa_decrement_exception_refcount(info.excPtr);
exceptionLast = 0; // XXX in decRef?
},

__cxa_get_exception_ptr__deps: ['$ExceptionInfo'],
__cxa_get_exception_ptr__sig: 'pp',
__cxa_get_exception_ptr: function(ptr) {
var rtn = new ExceptionInfo(ptr).get_exception_ptr();
#if EXCEPTION_DEBUG
dbg('__cxa_get_exception_ptr ' + ptrToString(ptr));
err('__cxa_get_exception_ptr ' + ptrToString(ptr) + ' -> ' + ptrToString(rtn));
#endif
return new ExceptionInfo(ptr).get_exception_ptr();
return rtn;
},

__cxa_uncaught_exceptions__deps: ['$uncaughtExceptionCount'],
Expand All @@ -285,13 +209,13 @@ var LibraryExceptions = {
throw exception;
},

__cxa_current_primary_exception__deps: ['$exceptionCaught', '$exception_addRef'],
__cxa_current_primary_exception__deps: ['$exceptionCaught', '__cxa_increment_exception_refcount'],
__cxa_current_primary_exception: function() {
if (!exceptionCaught.length) {
return 0;
}
var info = exceptionCaught[exceptionCaught.length - 1];
exception_addRef(info);
___cxa_increment_exception_refcount(info.excPtr);
return info.excPtr;
},

Expand Down
4 changes: 0 additions & 4 deletions src/library_exceptions_stub.js
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Original file line number Diff line number Diff line change
Expand Up @@ -7,10 +7,6 @@
var LibraryExceptions = {};

[
'__cxa_allocate_exception',
'__cxa_free_exception',
'__cxa_increment_exception_refcount',
'__cxa_decrement_exception_refcount',
'__cxa_throw',
'__cxa_rethrow',
'llvm_eh_typeid_for',
Expand Down
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