I'm pretty sure that the 4-byte alignment of you allocator is the problem
since emscripten (very likely) wants to access the double members through a
Float64Array heap view which has 8-byte granularity. On x86 CPUs memory
access don't need to be naturally aligned (except for SSE read/writes which
must be 16-byte aligned), but you should be aware that you're still paying
a performance penalty on Intel since the CPU has to use 2 read/write
operation for such unaligned memory access. So IMHO it would be a good idea
to make your custom allocator at least 8-byte aligned (16 if you want to
SSE).
There are a few -s Options which deal with alignment, may be these help,
but there will definitely be performance panelties (see
emscripten/src/settings.js):
var UNALIGNED_MEMORY = 0; // If enabled, all memory accesses are assumed to
be unaligned. (This only matters in
// typed arrays mode 2 where alignment is
relevant.) In unaligned memory mode, you
// can run nonportable code that typically would
break in JS (or on ARM for that
// matter, which also cannot do unaligned
reads/writes), at the cost of slowness
var FORCE_ALIGNED_MEMORY = 0; // If enabled, assumes all reads and writes
are fully aligned for the type they
// use. This is true in proper C code (no
undefined behavior), but is sadly
// common enough that we can't do it by
default. See SAFE_HEAP and CHECK_HEAP_ALIGN
// for ways to help find places in your code
where unaligned reads/writes are done -
// you might be able to refactor your
codebase to prevent them, which leads to
// smaller and faster code, or even the
option to turn this flag on.
var WARN_UNALIGNED = 0; // Warn at compile time about instructions that
LLVM tells us are not fully aligned.
// This is useful to find places in your code where
you might refactor to ensure proper
// alignment. (this option is fastcomp-only)
Cheers,
-Floh.
Am Montag, 11. August 2014 15:34:27 UTC+2 schrieb Sergey Solozhentsev:
>
> I have ga,e that is works on windows (an arm ios/android). And I need to
> port in on web. I have code that is warks fine for all previous platforms.
> However after compiling code using emscripten I found strange behaviour. I
> have class
>
> class CEnemy
> {
> ...
> wchar_t* version;
> double m_d1;
> double m_d2;
> }
>
> When I set m_d1 to some value e.g. 1.0 version field is also changed. I
> use special allocator to reuse memory for different objects. All values
> from this allocator are 4 bytes aligned. Without reusing memory it seems to
> work. However I'm afraid that using normal allocator slows down my game
> very much.
> adress of m_d1 is 4 bytes aligned but not 8 bytes aligned. Probably it is
> important.
>
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